This blog is a great start to 2012. Thanks. I have a suggestion for a discussion…post a brief summary of the differences in displacement choices for those of us still early in the engine build or still deciding? And a question…planning a West Coast Corvair College this year?
Good to hear from you. First, we are thinking of holding an event in California this year. We are looking at May 5th weekend in Chino at Steve Glover’s hangar where he runs NVaero. Steve is having a KR gathering there and an open house at his shop that weekend. I have known Steve for many years, and his two commercial hangars at Chino are well equipped to have a very productive College. Steve and I think that having the two events on the same weekend would be a good exchange of people and ideas. The Corvair is a very popular engine choice in the KR, and Steve wanted all Corvair builders to understand that they are more than welcome at his place. (Besides owning a series of KRs, Steve also has a Long EZ and a TriPacer; he is an all around aviation guy.) The only thing that has kept me from putting it on the schedule is a 50/50 chance that the weekend will conflict with my brother-in-law’s retirement from 30 years in the Army. In our family, such an event is “AHOD” (all hands on deck). We will know more in two weeks, and post the information here, under the “Events” heading.
On the subject of engine displacements: Today I encourage people to build one of three engine displacements that makes sense to them. Here is a breakdown:
2,700cc, 100hp, based on stock Corvair cylinders which are rebored from .020″ to .060″. Requires no machining to case or heads. Uses either Sealed Power or Clark’s Forged pistons. This is the engine that 85% of builders are working on. More than enough power for a Pietenpol or a KR, a good choice for a 601 or 650. There are many flying examples of each of these airframes with this engine displacement that have individually logged hundreds of hours each.
2,850cc, 110hp, based on Clark’s heavy duty brand new full fin cylinders bored .105″. Requires no machining to the case or heads, it is a straight bolt-together engine. This engine uses U.S. made forged pistons that are available through us. We sell a Piston/Ring/Cylinder/Rod Kit for $1,750. The pistons have a 7.7cc dish in the head to lower the static compression while maintaining a very tight quench area, giving the combination of good combustion and outstanding detonation resistance, even on unleaded fuel. The engine is also the best choice for later turbo-charging. The displacement is a good choice for any Corvair powered airframe. Photos of CC #19show Jeff Cochran’s running 2,850 built for his 750, and you can look at CC #21’s coverage for pictures of Clarence Dunkerley’s running 2,850 that he built for his Cleanex. Our Web site coverage of Oshkosh 2011has a lot of photos of Woody Harris’ 601 that he flew on a circumnavigation of the U.S. Woody’s plane is powered by a 2,850.
3,000cc (3 liter) engine, 120hp. This is based on custom machined cylinder castings that are related to VW castings. The bore size is 92mm, but we use the HD casting that is the same as a 94mm VW cylinder. The piston in this engine is the big brother of the 2,850. It is forged in the same U.S. factory, and features a 10cc dish. This provides the same combustion characteristics in a slightly larger displacement. This engine does require having the cases bored slightly for the larger cylinder spigots and having the head gasket area opened up slightly. This job must be done accurately, and the price is included in the Piston/Ring/Cylinder/Rod Kit. This displacement is a good choice for any Corvair powered aircraft. It has flown on both the 601 and 750.
Given these three engines, we no longer steer builders toward previous engines like the 3,100. There is nothing wrong with 3,100s, but they did prove difficult to build for many people without a lot of previous experience. The internal dimensions were a compromise because the 3,100 used a modified VW piston with a different compression height, requiring the engine to be built with custom length pushrods, etc. The 3,000cc engine was our clean sheet of paper, based on what we knew after 10 years of building 3,100s. A 3,000cc engine is a better engine from a number of angles, and is a better engine choice for builders considering using unleaded fuel in the future.
Every flying Corvair needs four pieces of cooling sheet metal that came from the factory. These pieces are the two under-cylinder baffles, and the two end plates on the firewall end of the engine that go between cylinder #1 and the distributor and on the other side between cylinder #2 and the oil cooler. These four pieces of sheet metal are just as vital to the engine’s cooling as a radiator hose is to a liquid cooled engine.
Because a lot of engines have very filthy or rusty metal, we have decided to make sets available to builders. They are very time consuming to clean, even if you have a blasting cabinet. I took a large collection of these pieces to our powder coating guy, and let him professionally blast them, and then powder coat them matte black.
They are not required to be powdercoated on your flight engine, but getting a set from us does save some time, and they look very nice, a good compliment to a sharp looking engine. We are selling these sets for $99 plus your old parts by check or money order payable to William Wynne, 5000-18 US HWY 17 #247, Orange Park, FL 32003. If your core came without, please send us $120.
Please email us at WilliamTCA@aol.com to let us know they’re on the way. We’ll reserve a set for you.
As an introductory offer, we are going to cover the shipping of our parts to anywhere in the U.S. We will do this through the first 10 sets in the shop.
Above, the two end baffles in the bag, the two under-cylinder baffles are below them. All of the parts are powdercoated matte black.
Above, 14 sets of under-cylinder baffles ready to be sent as part of the four piece cooling sheet metal sets. In the background, freshly done powdercoated Valve Cover Sets.
Valve Cover Sets are available for shipping in the U.S. for $159 by sending a check payable to William Wynne with your old valve covers to 5000-18 US HWY 17 #247, Orange Park, FL 32003. Please email WilliamTCA@aol.com with your choice of Red, Blue or Black as well as your horsepower or FlyCorvair.com designation.
When we assemble an engine, one of the steps that I take is to test the head studs before we put the case together. It is a quality control step, and if one of the studs is slightly weak, I want to know it before assembly because it is a lot easier to fix before you build the engine. The procedure is fairly simple, and the tooling isn’t very elaborate. I bring my set to Collegesand show builders there the process in person. Here, in a few paragraphs and pictures, you can get a good overview.
Based on building several hundred engines in the past 20 or so years, the chances of getting a weak stud are low. About every 10th engine will have one. These studs were overstressed on disassembly or were overdone on a previous build. They look good on the outside, but the stud has been taken past its yield point.
Above, the test set up.The test is made easier with a high quality torque wrench, but it will work just the same with a beam type wrench. The small spacer on the arm allows the same tool to measure the longer top studs. The little tube is just a collar for the spacer, not required. The ends of the tubes need to be fairly true to the tube, the best method is turning them in a lathe, but careful work on a belt sander will do the same task.
Backing up a moment, I am going to assume that you have pulled and replaced all the studs that had hard tool marks from previous owners’ vice grips, and also pulled all the studs that have harsh rust pits. Mild surface corrosion is not an issue, and a missing thread at the top of the stud on the fine thread end isn’t a reason for rejection either.
Many years ago, I taught engineering labs at Embry Riddle in the Materials Department. People who have been through these classes know what a Tinius Olsen pull test machine is. For the rest of the gang, it is an immensely strong set of jaws pulled apart by a very powerful hydraulic system. Many of these systems can pull 50 thousand pounds without bogging down. A test sample of material is put between the jaws and very slowly pulled apart, while computers measure the length and power of the pull. This all happens at a very slow rate, pulling 1/2″ can be slowed down to take several minutes.
Instead of demonstrating the machine on expensive test samples, I brought in bundles of Corvair head studs. We pulled them apart in every class. It gave both myself and the students a much better understanding of the effects of corrosion and mechanical damage like tool marks. A used Corvair stud in fair condition may not look that strong, but it takes over 10,000 pounds of pull to get one to neck down and break. Because of this testing I have a pretty good idea of what is too much damage on the outside of a stud. But the testing in these photos tells the condition of the stud on the inside of it.
The test tube is a piece of .188″ wall 4130 tube, 3/4″ in diameter. I welded a washer on the bottom it give it a bigger footprint. I polished the bottom of this so that it doesn’t leave any marks where the base gasket goes. On the top of the tube there is a very high quality hardened washer and an ARP 3/8-24 nut. (This can be done with lesser hardware, but remember, the goal is to test the stud, to the strength of the test hardware.)
Above, the washer and nut are in my hand, the tube is viewed end on showing the wall thickness. The tube has a little stand welded on it from a 2004 test series where we measured how much the studs stretched when they are torqued. At full torque, the studs are almost .035″ longer. This is an outstanding design feature. The engine is “spring loaded,” and the studs maintain their clamping force through a very wide range of engine temperatures, and expansion and contraction cycles. Engines like the Jabaru have very short bolts that hold the heads on. Bolts like that typically need continuous checking, because even a slight amount of material compression under the head of the bolt will result in a loss of torque on a short fastener. Conversely, a long stud is comparatively immune to this. Certified aircraft engines have the heads permanently screwed to their cylinders for a number of other design reasons, but engines like the Corvair, VW and Porsche all use the long studs. These are part of a well calibrated system, and are the primary reason why you should not use an aluminum cylinder on a Corvair. Porsche 911s eventually had aluminum cylinders, but they also had uber expensive “Delavar” studs, with an expansion and contraction rate that was compatible with their alloy cylinders. Companies that have offered aluminum cylinders for Corvairs have not taken expansion into consideration. Making the studs thicker or stronger actually only exacerbates the issue. Corvairs are designed for steel or iron cylinders, and they have an outstanding record of reliability with them.
Coat the threads on the stud and the washer with ARP Ulta torque lubricant. Drop the tube over the stud, run the washer down and then the nut. Carefully torque the nut to 15 foot pounds. Noting the clock position of the wrench handle when you start, raise the torque to 20 pounds. Typically this will require turning the wrench about 45 degrees on the short studs, about 55 degrees on the long ones. Next, raise the torque to 25 pounds slowly. Now, the critical observation: It should take the same 45 or 55 degrees of rotation on the nut to get the new torque increment. There is an acceptable range, and you shouldn’t be too concerned about a variation of 15 degrees or so. But, if you have a stud that requires 100 degrees of rotation to go from 20 to 25 pounds when all of the others took only 45 degrees, you have found a weak stud, and it needs to be replaced.
Above, the tool on a lower stud, giving a better view of the auxiliary arm on the tube from a previous test. The arm plays no role in this stud check up. Note the plywood under the case. Don’t let the mating surfaces sit on a steel table, concrete or any other rough or hard surface.
A weak stud undetected is not going to lead to an engine failure. Typically, when a builder has a bad stud, he is torquing up his heads and notices that one stud turns way too far. This is the point where it would have been better to test before assembly. But even if it goes undetected at this point, the typical stud will not break, it just will not be clamping as tight as the others holding down the cylinder. In time this can lead to a blown head gasket.
Above, the task in action. The torque wrench is a $300 Snap On item, pricey, but an outstanding piece of quality. Ours is called Excalibur. If you ever meet an A&P mechanic and he has a pair of sunglasses or shoes that cost more than his torque wrench, be guarded about taking his advice. Paul Gauguin’s paintbox was more valuable than anything else he owned. The brush doesn’t make the artist, and the tool doesn’t make the mechanic, but it is a measure of whether a man considers his work a craft or just a job.
A Corvair is a very tough engine, and I have seen several of them fly a long way on a blown head gasket. The engine makes power on the cylinder even if the gasket is blown because at RPM the compression doesn’t have time to bleed through a tiny gap. A blown head gasket on a liquid cooled engine is a different story because it can mean a loss of coolant either out of the engine, into the crankcase, or into the combustion chamber. Liquid cooling is better in theory, but air cooling is better in practice. (A liquid cooled engine is less likely to ever blow a gasket, but if the discussion is about aircraft, you are mostly concerned about how the powerplant behaves after the event, not just the likelihood of the event.) In Corvairs, I have seen about 10 engines with blown head gaskets in the past 15 years. Almost all of these were caused by the timing not being set with a light at the static rpm. Only one or two were caused by a weak stud. Both of these causes are easy to avoid. Testing your studs before assembly avoids a small chance of a hassle on final assembly.
On final assembly, be alert for studs that take a lot more rotation to reach the rated torque value. When studs are torqued with ARP ultra-torque, we have done very careful tests to prove that you are getting the same clamping value at 26 foot pounds as a builder with light oil is getting if he torques the stud to 35 pounds. Use ARP, and stop when you get to 25-26 pounds. If you go all the way to 35 you are exerting a lot more force than required, and will actually be doing damage. Remember, you got into experimental aviation for the learning and adventure. Take pride that successful Corvair engine builders know a lot more about how engines are really built than any other group in experimental aviation.
The following photo series is of testing a new High Volume Oil Pump that we had made. The assembly and testing covered about 5 hours on Friday night. When I was in my 20s, I used to make a point of donating 10% of my week’s pay to Anheuser-Busch corporation on Friday night. In the past 2 decades, I have found more productive things to do with weekends. Years ago, people saw how much time I spent at our old hangar and often said that I practically lived at the airport. After Grace and I were married, rather than trying to get me to come home from work earlier, she came up with the solution of moving the house closer to the hangar. For the past 6 years they have been 10 feet apart. Our hangar is 40’x50’, but I do most of the work in the adjoining 15’x30’ shop seen in the photos. Our hangar is a basic metal pole barn without insulation. The workshop is fully insulated and got an older central heat and A/C system installed last year. (We have a neighbor in the HVAC business who needed a Warp Drive prop.) Although we live on a little airport, working in the small shop next to the house gives me the same feeling I had when I first got started building planes in the garage behind my house at 1235 International Speedway Blvd., Daytona. Working in the shop makes me think about all the other builders out there working in their garages, basements and workshops, all the people enjoying the hours creating their plane with their own hands. No matter how diverse homebuilders are, they all have this in common.
Here is a shot of the basic unit. A high volume pump is basically a longer set of gears with some type of extended housing. The extended gears are from a small block Chevy V-8, and they are identical to a Corvair’s except they are .400” longer. The next time some brilliant guy in your EAA chapter tries to tell you that Porsche or Franklin designed the Corvair engine, you can ask him why he thinks the oil pump is interchangeable with a V-8. The Corvair is 100% Chevrolet engineering.
The extended housing on high volume pumps is usually a two piece affair that his held together with roll pins, it can be a little tricky to set up, and it does have some pumping losses from a less than perfect fit in the assembly alignment. It also has two gaskets in it. Above you can see that our housing is a one-piece bowl-shaped unit, CNC machined. Instead of aligning itself on roll pins, it centers itself on the two shafts, which are stabilized by the housing. This is not a new concept, this style had been made before by Corvair car racing guys. However, our unit was sized from scratch, and independently developed to serve aircraft guys. It is self aligning, has minimal pumping losses, and only has one gasket.
If you have been around Corvairs only a few years , this is a tool you may not have seen before. I built it many years ago to test oil systems. It is the back half of a Corvair case with a little sump added underneath. It has plugs welded in a lot of places to seal it, and the gauges are set to read oil pressure before and after the bypass. It has a valve to allow mimicking any bearing clearance and oil flow requirement. This part is actually a rare “RL” case from a 180hp turbo Corvair, but it is special for another reason: It flew several hundred hours in our Pietenpol. Over the years, we have tested many cases on this unit. After we moved to Gold Oil Filter Housings, we stopped working on rear oil cases for builders because most Gold Oil Systems use our replacement oil cooler bypass valve built into the Sandwich Adaptor. This unit was very good at detecting a marginal stock oil cooler bypass, in addition to testing oil pumps.
Over the years, I have made lots of pieces of custom testing equipment, because testing is the most important element that we do. Many people have an idea about making a part. If they have time and money, or they are amateur CAD guys, they can get a machine shop to make the part. Some of these will function, and a still smaller fraction will work with other required parts in a way that fits in the final installation. Some of these parts will actually pass basic testing. But the real testing requirement is not showing it will work, but aggressively trying to find the way the part, or under which circumstances, or in which combination it will not work. Few people understand that this is the real focus of testing. Most people who conceive of an idea, defend the concept, nurse it through manufacture, and then start testing it have a big emotional attachment to it. At that point, they believe in it. They have a very hard time trying to develop any test that will show the part or concept to be deficient or vulnerable. For testing to be of any real value, you have to run it as if it is being directed by your worst enemy, your ex-wife and her mother, and the guy at work who thinks homebuilt aircraft are crazy. For the period of testing, you have to pretend that these people have PhDs from MIT and Cal-Tech, and they want to find any flaw in your idea. You have to really let go of any emotional attachment to the concept’s success. This is really what running an effective test is all about.
Adhering to this over the years, we have tested a lot of ideas that never saw the light of day. All of the things we do make were refined by the process I just outlined. Our evolution in the development of the engine and installations was never hampered by an emotional attachment to the way we were doing it. Once a month or so, I will get a guy on the phone who will say something like “well you used to do it that way” referring to the set-up he is planning on using in his plane. He saw in an old photo on our Web page, and is yet to understand why it evolved. His attachment is understandable, it’s how we did it once, and he doesn’t see the forces that drove the evolution. I talk a lot, but I am also a very keen listener, and in the conversation I can hear if they guy has an emotional attachment to the old way, and if he is resistant to the logical reasons why it evolved. You don’t have to build your Corvair the way we do, but when evaluating your choices, be very cognizant of the emotional attachment factor creeping in and not letting you truly evaluate the merits. Homebuilders by their very nature arrive in the field wanting to do something different. They are reluctant to be seen as conformists. This is a good concept, but it can also work against the practical goal of completing the plane. If 10 new guys all look at the logic of why we build engines the way we do, evaluate it, and then choose to build their engines that way, this is not a sign of conformity, this is critical thinking leading many people to the same point. There will always be some guy on the Net who criticizes this and tells everyone how his engine is going to be totally different, that is once he gets started building it. 20+ years of working with homebuilders has taught me that the odds of that person flying anything are microscopic. But it isn’t primarily because his idea is bad, actually the Achilles heel of his whole concept is that It is emotionally driven by a force that has very little sustenance in it, the concern for what other people think of you.
In the background, a selection of oil pump gaskets in different thicknesses. This is how Corvairs set the pump clearance. After test fitting them, and checking for a slight drag on the pump while turning it, I settle on a .007” thick gasket and give it a light coat of spray copper before sealing it up.
Here is the unit all buttoned up, Yes, I ate dinner at the workbench.
The drill bit is pointing to the pressure regulator bypass hole. It has to be opened up when you install a high volume pump. Otherwise the pressure will be very high until the oil temp is thoroughly warmed up. The enlarged hole allows the bypass to work with cold thick oil. Without enlarging this hole it might take 15 minutes of running on the ground on a 40 F day before the oil settled down to its normal regulated pressure. Before this, an increase in rpm will raise the oil pressure. On very cold start ups you want to watch this, because even with the hole enlarged it is possible to have the oil pressure exceed 80 pounds by carelessly revving the engine to taxi it while the oil is still cold. Give the engine a chance to warm up, don’t be in a rush. Oil pressure spikes are very rough on the drive system running the pump. This is true of almost all engines, not just Corvairs. People don’t talk about ideas like this with the buy-it-in–a-box imported engines because they just wanted to buy something and use it. Since the primary motivation with Corvair builders is to learn while creating, we talk about things. Most people are happy to just have things, people attracted to the Corvair were the ones who took apart the toaster at age 10, because for some of us, we need to know why.
This plug holds in the spring and the pressure regulation piston. Make sure your piston is polished and the bore has no burrs left over from enlarging the hole. I use a copper crush washer for the gasket. I use the higher pressure spring from Clark’s. The wrench size is 13/16” but it has small fine threads, so don’t do more than 15 foot pounds or so. I do not safety these, and I have never seen one get loose. This plug is shiny because I nickel plate them.
Above is the unit in action. It is being driven by an electric drill on a priming shaft, just the way we prime the engines at the Collegesbefore we run them. After running through the system, the oil is returned to the center of the case by the 3/8” aluminum hard line on the right; it is entering the case where the #1 cylinder was. Notice that you can actually see the oil stream flowing in the photo. From there it goes back in the bottom of the case and is sucked into the pickup again. The new pump flowed like a river, even at very low rpm. We are going to let it run for a long time in the shop this weekend, with the drill trigger held down with a zip tie. It will be noisy, but I have my sister’s old 1970s stereo that she bought with babysitting money in the shop, a hold over from when people cared about sound. 120 watts, Ohlm speakers and an extended cut version of Exile on Main Street and I will never notice the sound of the oil pump rig running all weekend. Monday we will take it apart and look for any wear on the inside.
Grace and Scoob E were out in the shop helping with the project. Above, Grace ran the drill during the set up tests. This rear cover will have a Gold Oil Housing on it when it is finalized, but for testing, I have it set up with one of our old style oil top plates from the 2004-2007 era. You can see the built-in pressure gauges in this photo.
It wouldn’t be Friday night without a little fun. Our neighbor Roger was having a cookout and a bonfire in his front yard just down the runway. We missed dinner, but arrived in time for the relaxing around the fire with a beer phase. Most builders know that the one pound cooling fan on a late model Corvair car is made of magnesium. We brought one down and after warning those present, tossed it in the fire. It ignited after a minute of warming up. For five minutes you could have seen our airport from low earth orbit. The camera doesn’t do the event justice. It illuminated the entire southern end of the airport; you could have read a newspaper 500’ away. At most airports this would have brought firefighters, hazmat people and the news media. At our airport it brought more people with beer. As a little kid, I played with matches, built tree houses, took apart the toaster, made go-carts and was known on a first name basis at the emergency room. My test methods have gotten a lot better than childhood forays into chemistry, but my incessant need to know remains the same. I accept that the majority of people in life have a consumer mentality that tells them that simple possession is the route to happiness. For the rest of us who know that our path to happiness is learning and creating, we have the Corvair movement. The Harley Davidson slogan, “If you have to ask, you wouldn’t understand”’ is a modern version of George Mallory saying “Because it’s there” about mountaineering. The first statement has become something of a cliché, and many of the people saying it are concerned with what others think, but Mallory was deadly serious that he was not going to lead his life by the mundane concerns of others. My mother taught us to be civil to everyone, but even as kids, there was a clear distinction between always being considerate of others, and leading your life by what other people think. It was an important inoculation that protected me, especially in my teenage years, from peer pressure and the things it leads adolescents to. In the long run, it made me comfortable following my own path, with little concern for what the larger group thought I should be doing. The Corvair movement is a reflection of this, and if you feel the same way, I say “Welcome aboard.”
Dan Weseman, the man behind the Wicked Cleanex, The BTA 5th bearing, and the Panther project, the second winner of the Cherry Grove Trophy, is working his way toward a new goal is the land of Corvair powered flight. He is developing a made in the USA, true billet crank for Corvair flight engines. Follow this post and get an inside take on his motivation and the challenges involved.
Above, Dan in his new 12’x50′ climate controlled workshop built inside his hangar. He built the space to facilitate the development of and the eventual production of “Florida Panther” aircraft. In the photo are a fuselage side for the steel tube sub frame and an aluminum wing rib. Although the plane is intended to be an LSA legal, fun flying plane, Dan is building in enough strength for some advanced aerobatic work.
Dan Weseman has a well earned reputation in the world of flying Corvairs as a get it done kind of guy. Outside of aviation, people are impressed by people who get a lot done in a day. Inside aviation, accomplishments are done on a longer time scale. Building a plane has an element of “What can you get done in the next 4 hours?” to it that is very important. But it also has the requirement of stringing together a long series of these work sessions. Lasting accomplishments are built of this type of sustained efforts.
Dan often takes a modest tone on the outside, saying things like “we will see how this works” in discussing projects, but knowing him for many years, I have come to see that such comments are really to keep discussion low, and they address the fact that many new arrivals in experimental aviation are yet to see the sustained effort required to bring anything good to physical reality. Downplaying the discussion side of his efforts is a way that keeps Dan operating the project on his schedule, not on anyone elese’s expectation.
This has proven to work well in the long run. Dan, in joint effort with his father Jim, have now delivered more than 200 of their 5th bearings to Corvair builders. The bearing story is one of careful development and testing followed by steady customer support. Same goes for Dan’s efforts making “Cleanex” Corvair installation packages available to people building Sonex airframes. After building and flying his own aircraft and refining the installation, Dan moved to making the parts available. His installation components are compatible with all of our engine components. We even developed some parts, like the Reverse Gold Oil Filter Housing and the Universal #1 Exhaust specifically for Cleanex installations. The engine installation has been a steady success story. When I visited Dan’s shop there were 5 more Cleanex mounts in process being finished by master welder Vernon Stevenson.
Dan is now turning this approach to the subject of billet crankshafts. While other people have thought of this before, and Corvair race car guys have had a handful of them made by crank specialty shops over the years, they have not shown up in experimental aircraft. Here is where Dan’s unique background comes in. For a day job, he installs CNC machining equipment in industrial production shops in the southeastern U.S. His company deals with the transportation and installation, so he gets to work with all types and brands of machinery. He has been inside more machine shops than any other person I have ever met. He fully understands which type of modern equipment is best suited for making a run of billet cranks for high stress Corvair engines. Combine this with his background as a builder and a flyer, and the experience he has in bringing parts to the market and supporting them, and you have the makings of a success story.
A billet crank is made from a piece of round stock, typically in the case of the Corvair, a cylinder 6″ in diameter and two feet long. This material is most often 4340 alloy steel made under exacting conditions. This cylinder itself is a forged piece of material, not cast. Professional race car engine builders specify that these blanks be made in the U.S. with a paperwork trail that demonstrates their pedigree. Because 80% of the material in the blank is going to be removed to make the crank, it must be guaranteed to be homogeneous throughout the blank.
Hand making these cranks in a crankshaft shop is one of the reasons why they typically cost $3000. The material removal takes a long time on traditional equipment. Many crankshaft shops only have the reserve manpower to make a few of these a year. Dan is looking into a different approach, where he is going to have 98% of the material removed by very powerful CNC equipment, bar feeding lathes that can work from a 20 foot long billet. As a second step he wants to take them in groups to a crankshaft specific shop like Moldex, where those craftsmen will be able to put the finish grind and balance on the part. He is working toward driving down the price toward $2000-$2500 with a new gear installed.
Such a crankshaft can be made stronger than the original GM forged crank. Contrary to what many people think, billet cranks are not inherently stronger than forged ones. The grain of a forged crank actually makes it stronger than a billet in direct comparison. However, automotive cranks do not have large radiuses in the fillets. In cars they are not required. Purpose built aircraft cranks have much larger radiuses, reducing the potential for a stress riser. Billet cranks can be built with large radiuses, and this allows them to potentially withstand extreme forces better than a forged crank with smaller radiuses. At times, discussion on crankshafts is driven by people who don’t have a grasp on concepts like this. Productive understanding starts with a practical look at how the concepts are applied to our specific engine. Commentary without this isn’t worth serious consideration. People will always throw around statements like “they are 20% stronger.” No statement like that makes sense without addressing tension, torsion, bending or fatigue life. The real discussion is a far greater in depth, while focused on a far narrower scope.
A number of people think that the genesis of Dan’s billet crank project was when Mark Langford broke the back end of his KR-2s crank in November. In reality, Dan had long been planning on having a billet crank as an experiment in his new aircraft, the Panther. In his own style of letting the project set the timetable, not public discussion, he was working quietly on the topic, developing the plan as he worked in a number of different CNC shops that have the equipment that would make the project economically viable. After Mark’s comments, some builders started asking about billet cranks, including Chinese ones. In an effort to let people know that he was working on a U.S. made one, Dan mentioned this, and has a small email list of people who are following his progress. Mark Langford is one of the people who has said he will use one of Dan’s cranks in the next incarnation of his engine. To be clear, Dan’s interest in the development was driven by the fact that he is going to set up his personal Panther for some very hardcore aerobatics. He has told me he wants to use the Precision mechanical fuel injection we have for testing, and he is even considering an inverted oil system. In his 3,100cc Cleanex, Dan flew a tremendous amount of sportsman aerobatics on a stock GM crank. He did a lot of this without a 5th bearing. After he developed his bearing he retrofitted it on the same engine/crank and kept going. Over several hundred hours of hard flying he has not had a crank issue with either the nitrided crank by itself nor his 5th bearing. When it comes to flying like that, most people recognize that it makes sense to have a 5th bearing. Likewise, now that Dan is moving up a notch in the stress department, going to a large radius billet crank is just part of his plan to make sure that he has 200% of the strength he needs, not 99%.
The most common question that people have about these cranks is “Do I need one?” My primary answer for this is that the vast majority of builders do not need one of these. That is my opinion based on the big picture of statistical evidence we have from being at the center of the Corvair movement. I have seen Dan fly hard aerobatics at wide open throttle in his Cleanex for 30 minutes at a time on a stock GM crank. We have pilots like Andy Elliot who have flown hundreds of hours on a 3,100 without a 5th bearing. Mark Petz overhauled the engine in Bernard Pietenpol’s Last Original last summer. It had 800 hours and the crank was perfect, in spite of never having been nitrided and not having a 5th bearing. We have a lot of pilots with several hundred hours on non-nitrided cranks and no 5th bearings. It is all a matter of personal choice. Very seriously, I am not, and do not wish to be, in charge of anyone eles’s building, flying or life. The primary attraction to me of flying is freedom, and the root of this is being able to decide things for myself. I am not here to take that away from anyone. I take presenting the facts very seriously. I take countering disinformation seriously. I take the task of explaining the risks very seriously. I want builders to know the big picture. But I fundamentally trust that anyone who is rational enough to fly a plane can make the correct decision for themselves, given factual, accurate information presented without emotion. If I came out and said, you have to have a nitrided crank, a 5th bearing, or a billet crank, or I will not work with you, then I am dictating that our accumulated knowledge will only be shared with some people. I make strong recommendations, demonstrate that I believe in these recommendations by building engines that match them and flying behind them. But, in the final measure, builders are going to make their own decisions.
New people will often say, “Just tell me what to do” in homebuilding. This is ok when you’re getting started in homebuilding. Most of these people get off to a good start by replicating the engines that we build in our shop. Over time, this same person needs to transition to the mindset where they are analyzing the available information and making the decision for themselves. I want builders over time to understand the logic of all of the choices we make in our work. They are not required to agree with the choice, but it is not a sign of conformity if two people look at a set of facts and come to the same conclusion. Making choices for yourself is what being in command is all about. This is how you prepare for being aloft, especially with another person in your plane. It is the great reward of flying. Self reliance and earned self confidence also happen to be your best line of defense in any flying situation.
In modern life, people are less and less in charge of important decisions that count. On many fronts, society is trying to prevent you from hurting yourself, and the method they choose is most often taking away the ability to do so, not educating you and letting you choose the path. Flying, and homebuilding in particular, is the polar opposite of this. You have to have a really negative view of individuals to buy into a system that tries to prevent people from having the means to hurt themselves…The queen and the hive dictate to the worker bee his limited task, and when he has fulfilled it, he is no longer of any common good, and he is expected to die quietly because the hive programmed him to do so… In my book, humans are individuals, not insects. Any person who chooses do something simply because he wants to is affirming this. Any person who picks up a tool and sets out on a journey to create something of his choosing, a goal that does not serve the hive of society, can expect both the disdain of the hive and the warm welcome of other individuals.
If the pictures on this story are small, try clicking on the F5 key at the top of your keyboard.
Every now and then the subject of having a new crank made comes up. With a little reasearch on the Net, people find out that new cranks have been made for Corvairs. These fall into two groups: Billet cranks made in the U.S. for Corvair race cars, and cranks made in China.
In this post, I am going to speak about the latter. First, let me say that a lot of people make comments or hold very stong opinions about things they have never seen. Most people are guilty of this in one way or another, and it’s mostly harmless. However, when the subject of airplane building is at hand, I always want to listen to a guy who has first hand knowledge, because in aviation, the results of poor information isn’t always harmless. When I speak on the same subject, I am very careful to make sure that the person reading or listening is getting an accurate picture, and that they also understand the parameters of the discussion. On the subject of Chinese crankshafts for Corvairs, I think that I have a particularly informed opinion, not because I understand the engine, but because I have also seen the Chinese cranks in person, I know the guy who had them made, was present when they were inspected, followed their issues, and I know the only guy who has flown one. Follow through this story with me and get an insider’s look at these cranks, and then decide for yourself how you would feel about flying behind one.
The story starts with Brady McCormick of Washington state, about 2006. Brady is a good guy, and a heck of a good craftsman, but he isn’t an engine guy nor has he ever had any kind of aviation training. He likes the Corvair for his own aircraft, a 701 he is slowly building from plans. He buys a lot of core engines, which all turn out to be early models which have short stroke cranks. Over several months he hatches a plan to have new cranks made. He starts looking around the U.S. and finds that billet cranks cost $2500 to $3000. He finds a Web directory run by the Chinese government to direct foreign buyers to Chinese manufacturers. By contacting an agent in Taiwan, Brady finds out that new forged cranks can be made for about $1000. Brady was going to use these to build engines and also resell them to builders. Quite a plan for a guy who had never built a running Corvair engine of any kind.
The catch on the plan came up quickly. The Taiwan agent stated that she needed $30,000 to have new forging dies made, before the cranks could be made on the mainland. To get started, she offered to have 5 cranks made from billets. These could be done without having dies because billets are just machined from round stock. Brady sent a sample crank, money for 5 billets, and a large deposit on making the forging dies. At this point he honestly thought that everything was going to work out, and that he was making a regular business arrangement, just as if he were dealing with a U.S. based company. Although I had not met him in person at that point, I regularly spoke to Brady on the phone, and as I listened to his great plan, I honestly thought his money was gone and he was never going to get anything. Something worse happened. They sent him the 5 billet cranks. Encouraged by this small first transaction, Brady borrowed $30K from his father’s retirement savings and sent it to pay for the forging dies. On that day he felt he had just made a move that would make his fledgling business “Magnificent Machine,” a major player in the experimental market. The long run would show something very different had taken place.
When Brady first announced his new cranks and put pictures on the Web, it started an Internet flap because they didn’t look like normal billet cranks, and Brady was prone to making statements about them that he couldn’t back up, like “they are 2.5 times stronger than GM cranks.” This was just stuff that he read on Web sites and wanted to believe. When he encountered people who actually had a university background in strength of materials, he was reluctant to admit he might be wrong. It was a rocky introduction.
I met Brady in person at the Arlington airshow shortly after. He was very different in person than what he projected on the Web. He was modest and much younger than I expected. In 30 minutes I decided I liked him and even though I am not a fan of things imported from China, I was moved by his desire above all else to return his father’s investment. I counseled him to change his Web site and online claims, and act more like his in-person self. I invited him to Corvair College #13 and he showed his stuff to our builders. At this show, Roy from RoysGarage.com was also a technical guest of mine. Roy took Brady aside quietly and showed him that the cranks were of marginal accuracy, and Brady should tell his source that the concentricity needed to be a lot better. Brady had two cranks that were 3.00″ stroke (instead if the stock 2.94″), Two that were 3.125″ and one that was 3.25.” To give you an idea of how much planning was missing, a 3.25″ stroke crank had the connecting rod actually hit the cam lobe on rotation. Brady had enthusiasm but not experience.
The first guy to buy a crank from Brady was Steve Makish, a friend of ours and a well known KR pilot of great experience. Steve understood that this crank was unproven, something of a test. He felt like he was a good guy for the job of test pilot. He bought a 3.00″ crank for his engine. After the short block was assembled at Dan Weseman’s with one of his bearings, Steve took it home to finish it. This is when he discovered that the rod throws on the crank were ground almost 1/8″ too wide. If assembled, it would have marginal oil pressure. Brady was informed, and he went out of his way to fix it; the best solution was having a custom made set of connecting rods. This took many weeks.
When the engine was assembled and run, Steve did his usual extensive ground run. After a long time, something didn’t seem right. Compression dropped off, and an inspection showed that the exhaust valves were bent. Usually the only thing that can do this is putting the cam in several teeth off, something a lifelong motorhead like Steve isn’t likely to do. After some time, it was noted that the keys on the back of the crank didn’t match the ones on the flange. A careful inspection revealed the following photos. The crank had been made undersize at the factory, and instead of scrapping it, they had made a hidden repair that had failed. Very luckily, this happened on the ground.
Above is the sleeve that was put on the crank. The stock crank has the same diameter as the outside of the sleeve. In this case, the Chinese had all the crank forces going through the thin section with threading on the inside.
The people who made this crank sold it to the broker in Taiwan who then sold it to Brady, He paid about $900 for it. I am pretty sure the shop in China that produced it had a tiny fraction of that amount of money in it. How cheap were they that they didn’t just trash this one and make another? They knew that this was going in a plane. They could read Brady’s Web site. They didn’t care, they were far away, and they were never going to get sued.
If you don’t know a lot about Chinese business ethics, you could easily dismiss this as a million to one chance of happening again. If you know a small sampling of their business culture, you will understand that this is a chronic problem in buying something from a country that doesn’t have the same ethics we do. I am not condemning the people of China, I am just pointing out that there is no rational reason to think that any businessman operating at Brady’s level can expect the kind of quality that is needed in aircraft parts.
Brady got Steve another crank and bought back all the other cranks that he had sold. He had a lot of money and time in his business, and he did listen to counsel about working his was out, but he had a gambler’s heart, and his approach was to double down on his bet. He borrowed more money and had another Chinese company make connecting rods. He ordered 500 piston blanks from a U.S. piston maker. He imported aluminum cylinders even though a number of people told him that these things would have long teething problems at best. All of this was done before Brady had built one single engine. I held a small College at his place, tried to get him to work on more modest things that would provide some cash flow. He listened while you were there, but he drifted back to his previous ways later. In the end, the Chinese kept all his money, he lost his business, his house, and a lot of the other things in his personal life unraveled. It was a long way from wanting to build a 701. It needs to be understood that he closed his doors after taking care of all of his customers. The only thing he kept was the one thing he was most concerned about losing, the thing that was probably never in jeopardy, his relationship with his father. His dad stuck with him all the way through.
One other issue has emerged with these Chinese cranks. Although they were always said to be made from billet, they don’t look anything like U.S. made billet cranks. Two people who know machining very well, particularly how cranks are made, both of whom saw Brady’s cranks in person, told me that they believe the cranks are cast steel. I listened to their reasons very carefully and I have come to agree that their argument makes a lot of sense. The Chinese are known for making millions of cranks from cast steel, it is an inexpensive process that yields a part that will work in an automotive application. The hidden defect tells me that anything is possible from China, and telling people that the cranks are billets when they are cast is not a moral problem for them. Today a Corvair car business in the southwestern U.S. advertises that they have these same cranks, and it refers to them as billets. The guy has no background in experimental aviation nor metallurgy, but he aggressively tries to steer aircraft people into buying them. No one should buy one of these for an aircraft. The Web site sells lots of untested parts, much of it sourced from the same people who made Brady’s cranks. There is one important difference between Brady and this guy: myself and the rest of the Corvair All Stars were doing what we could to get Brady to make better decisions and be more informed. He has willing to learn. The guy in the southwest has no such inclination, he just wants to make money off builders.
Although lawyers get blamed for a lot in U.S. aviation, I am going to make the case that you don’t get to see the good that they actually do. Putting emotion aside, think about this: Every year, countless people from outside of aviation refuse to sell products to, or work with, aircraft builders, citing the reason, “I don’t want to get sued.” Some of these people make good stuff that could be well used in experimental aviation. But a number of them make trash, or things that are not appropriate for planes, many of them have no idea of how aircraft work, and most of them have never even flown in a light plane. If those people make stuff for planes, and claim that their stuff is airworthy, they would get sued. The threat of legal action does keep good things out of the market, but it also keeps trash like the crank pictured above out also. That is unless the crank is made in China. You are never going to successfully sue anyone in China, their police state would never allow it. Their manufacturers don’t even have to consider it as a possibility. I am speaking from some level of being informed here. Friends of ours know that my brother-in-law is a partner in one of the world’s largest law firms. He is a global expert on international intellectual property, and has made countless trips to China since the early 1980s. He has said many times that you would never even get through the discovery phase of legal action against a Chinese company. The Chinese know this, and it means that they are more afraid of telling a production manager that they messed up a crank than they are of getting sued by the family of a guy who lived far away in a place they will never visit.
On an Internet Discussion Group, a well intentioned but misinformed homebuilder stated that he felt Corvairs should be built with new crankshafts and rods like other alternative engines. He further stated that he would not fly behind an engine built with used parts. Here’s a reality check: Virtually every person reading this who has flown in a certified general aviation aircraft in the United States has flown behind used crankshafts and rods, many of which have seen more than 10,000 hours of service. The overhaul practices, including magnaflux inspection, have long proven that people can safely take to the air with these components if they’ve been properly inspected and overhauled before assembly. The Corvair is no different. There are reasons why some builders might want a different crank for an extreme engine, but just feeling that any new crank is better than a reworked original one is an argument that seemed logical to Brady, a guy with no aviation experience. In reality, the Corvair has been flying for more than 50 years, and there is a known database of tens of thousands of hours on the GM crank.
If you look at automotive crankshafts, companies like Eagle and Scat have long histories of having cranks made in China. Tom Leib is the president of Scat. I have met him in person several times. A few years ago he wrote a long article in a manufacturing trade journal about the challenges of quality assurance in Chinese manufacturing. His thesis was that you’re going to get the lowest quality they can supply until you have your own people, who are ethnic Chinese, but paid for career long loyalty to you, on site where everything is done. Post process inspection in metallurgy didn’t count in his book. He felt that only major players would make it for this reason. The numbers he was speaking of to make this arrangement possible was 20,000 cranks per year. If you read the article, you will understand why Brady’s venture, or any plan to purchase from the Chinese that could be done by people in the small scale of Corvair flight engines, would end badly. I have good reason to say that Chinese crankshafts are not a good idea in Corvair aircraft engines. As we go forward, there will always be people who bring up the subject. If they do, ask yourself, what has changed since the factors that produced the defective crank above? I don’t see the nature of Chinese business changing, I don’t see a post manufacturing inspection that I would bet everything on, and the level of production will never allow on site inspection. For the Corvair movement, Chinese crankshafts are a dead end.
A lot of people thought my primary objection to Chinese cranks is that they were made in a communist country, where civil rights don’t exist. Other people thought that it was my bias for buying things made in America. I have said that I detest totalitarian governments, and that I make every effort not to support them economically. Yes, I have always tried to support American manufacturing and jobs for our countrymen, even before 1 out of 8 Americans was unemployed or doing work below their skill and dignity. But I can make a good case against using aircraft parts made in China to a guy who doesn’t particularly care about human rights or jobs. It is up to each individual to decide what is right for his own aircraft and the people who will fly with him while he is pilot in command.
Above are two of our powder coated modified Valve Covers. On Tuesday we are taking another batch to the powder coating shop in Jacksonville. We will have more sets of red, and the new blue will match the Old Ford Blue that we have traditionally used on FlyCorvair.com stuff. The above blue is known as Royal Blue, and we have one set left of these. We are getting several more sets in black, and on Tuesday I will try to get any custom color that builders like, if they order the covers this weekend. The Valve Covers come as a pair, the other side has the oil breather line fittings. You can have your choice of Valve Cover stickers: 100 HP, 2,850 cc, 120 HP or FlyCorvair.com, just please let us know with an e-mail to WilliamTCA@aol.com. If you would like more information, read the November 2011 Hangar Update page of our FlyCorvair.com Web site: http://www.flycorvair.com/hangar1111.html
Helicoil vs. time serts: Had to remove the top case studs due to completely corroded studs. Helicoil is what you recommend. What about time serts?
Thanks for the question. In the photo below, you have time sert tools on the extreme left, and the other three packages are popular variations on the helicoil concept.
I have used all of them over the years. They will all work, and any of them will hold in the case the full strength of the stud, if the stud is installed with Loctite 620 upon assembly. Given a preference, I would pick a time sert, but it is just a style point, not a major issue. The time sert stuff is a lot more expensive than helicoils. If you look closely, the thread on the Recoil box says 5/16-18; this is for other places on the engine, I just had it handy for the photo I shot a few minutes ago. The thread for case studs is 3/8″-16. This type of repair is something that we demonstrate at every College. They are not difficult to do if an experienced guy shows you once. I have put literally several hundred of these in Corvairs that have gone on to fly for many years. My own personal engine has about 30 of them in it. When done correctly they are stronger than the original threads.
We received this from Davis DA-2A builder Carl Luhning in Canada:
A recent comment regarding the a Harmonic Balancer coming loose leads me to wonder if I have installed mine correctly.
I used the called for Loctite for shafts and tightened it to the proper torque using the correct bolt for the purpose. I did not however use Loctite on the threads of the bold. Should I have and if so which one.
Thank you for your reply.
Good to hear from you. Follow through these photos and descriptions, and you can verify that your balancer is correctly installed. I would like to emphasize that having a properly installed balancer come loose is unheard of in the land of Corvairs. GM made 1.7 million Corvairs, and about 600,000 of them left the factory with a balancer installed. Over a lot of years, the original rubber elastomer could rot, and allow the outer inertia ring to slip or wobble. If you read stories from car guys, this is the type of problem they are talking about. This is why we tell people to get a rebuilt or new balancer with modern synthetic elastomer. But the point is that the hub itself, where it fits to the crank, is not a common issue that builders need be overly concerned about, with 2 exceptions that I will bring up further down.
The abovephoto shows the stock washer and bolt that hold the balancer on a Corvair. The bolt is a grade five 1/2″ -20. The washer is a very special part made by GM. It is made of heat treated steel, and it has a very slight concave surface on the side that touches the balancer. When it is tightened, this washer goes flat, and spring loads the bolt tight. This is why in its stock form on the car, it doesn’t have a lock washer nor Loctite applied to it. The “bevel” washer is doing the locking task. On cars, this system works flawlessly. On aircraft, it works great also. However, it is important to note that some people who choose to use a rear starter assembly do not have this washer incorporated in the system. Our Pietenpol had a rear starter from 1996-2001. It had an aluminum Puck that held the ring gear onto the balancer. This Puck had a pocket on the rear face of it so that I could use the same washer with a longer bolt. In 2009, we built several rear alternator set ups for engines that had our standard front starters. These had a Puck like part that also had the v-belt pulley. On these systems, I made sure that we had a provision to safety wire the mounting bolts in lieu of being able to use this washer. If a builder uses our standard front starter/front alternator, he just used the GM washer and bolt on his balancer, and he will have the same reliability that the cars have experienced.
The above photo shows that the GM washer is nearly 5/16″ thick. It takes this thickness to do the job of only going flat when the full torque is applied to the mounting bolt.
Above is a photo showing where the washer fits in the balancer. The balancer shown is a rebuilt DaleMfg.com unit.
Above is the bolt and washer going into its pocket on the back of the balancer. When I install a balancer I do not use Loctite on the threads of the bolt. I use oil on them. This will not affect the ability of the bolt to stay put, because the special washer is doing the job, not friction on the threads. Rebuilt balancers come with a special tube of Loctite that goes on the inside surface of the balancer, where it would contact the crankshaft itself. This takes up any space that may have developed over years of use. There are also new balancers sold by Clark’s that have a precision fit, but I would still consider using the Loctite because the crank itself may have experienced slight wear having the balancer removed and replaced in the past.
When the balancer is correctly installed on the engine, there is a gap of .150″ or so between the balancer and the pad with the timing marks cast in it.
Above, the part in my hand is the oil slinger that goes on the back of the crank, aft of the brass timing gear. This part is installed before the rear case goes on the engine. It is loosely floating on the rear of the crank until the balancer is installed. When the balancer is mounted all the way, this part is firmly clamped down. After the balancer is installed, this part can be seen by looking down the distributor hole.
Above, the last step in the process is to reach your finger down the distributor hole and touch the oil slinger. If the balancer is down all the way, it will be tightly clamped in place. If the balancer isn’t all the way down, even slightly, the slinger will have a detectable wobble in it.
Above is the other issue about balancers. If you look closely, the cross sectional area between the keyway and the outside seal surface of the balancer is only .125″ (1/8″). On cars, this has never been an issue. However, on aircraft there are two things that can cause a problem with this. First is a prop strike. If your engine experiences a prop strike, this keyway is going to get stressed. The balancer has a fairly high rotating moment of inertia. In laymens’ terms, it wants to keep rotating, and the fit between it and the crank, and the shear value of the woodruff key is all that is stopping it. Experience has shown me that in an overload between the crank, the key and the slot in the balancer, the loser is most likely to be the balancer cracking through the slot.
The second thing that some planes have that cars don’t is rear starters. The rear starter ring gear weighs less than the 5 pound balancer, but it is larger in diameter. It roughly doubles the rotating moment of inertia. In a prop strike, it goes after the keyway savagely. At Corvair College #13 in California, Pat Panzera brought out a rear starter engine that he purchased from a guy online. It happened to come from a builder I had visited in Florida, right after he had a prop strike ground running his Baby Ace without the tail tied down and without the wings on it. When Pat brought the engine to the College to run it, the engine showed very poor starter engagement. At first glance someone thought the crank was broken at the back, but upon a little digging the issue showed that the keyway on the balancer had split to the seal surface, allowing the balancer to become loose and the starter ring gear mounted to it to wobble.
In the above photo I have a hub from a GM balancer that I hit with a 24 ounce ball peen hammer about 5 times. What I would like people to look at it is the surface of the material where it broke. The photo isn’t great, but the material is clearly porous. It is cast material. It you put it on a grinder, it throws yellow-orange sparks, indicating that it is some sort of cast steel. (Cast iron on a grinder throws a more reddish spark.) Material like this works, but it isn’t as strong as if it were a billet part or a forging. GM engineers knew what they were doing and there is nothing wrong with this part for the task it was designed to do. The only issue that comes into play is when this type of cast material in a section only 1/8″ thick is subjected to an excessive load asking the part to absorb a shock load, be part of the starter system, or both. Rear starters work, but when they experience an overload, or if the mounting hardware is not safetied with the stock washer or wire tied, the balancer keyway stands a good chance of being damaged. This is the primary reason why a balancer on a plane would ever come loose. Excluding the issue of prop strikes, there is no issue for a person with a Front Starter to be concerned about.
Rear starters have been used for years, and our Pietenpol flew several hundred hours with one. They work. However, basic observation shows that they work the keyway much harder than a standard front starter installation. We are not just speaking of prop strikes. All the force of starting the engine is transmitted through the crank to balancer fit and the keyway. If the timing isn’t set correctly or the engine kicks back on cranking, there is a tremendous amount of force going through this area. If you have some doubt about how strong a starter is, ask any mechanic if they are powerful enough to bend a connecting rod in an engine that is liquid locked or has a piston stopped by mechanical interference. The three Corvair flight engines that I have seen that have broken a balancer through the keyway have all been rear starters.
This is not an across the board condemnation of rear starters. It is just a frank discussion to remind builders using them that they have things to stay observant of. It is also to remind all builders that when people discuss an issue, it may or may not apply to your aircraft. Today, more than 90% of the flying Corvairs use front starters. These engines have a good track record just like cars because they use the balancer and its hardware just as it is used in the car. Rear starter installations have different hardware, more weight, starter forces and a higher moment of inertia to contend with.
Over the years a number of Corvair powered aircraft that began flying with rear starters have changed over to our Front Starters. Two examples that come to mind are the KR-2s of Steve Makish and Bob Lester. These planes began flying on Corvair power is 2000 and 2001 respectively. They both originally had rear starters. Over the years, these two guys tested a lot of different ideas, some good, some not so good. They were open minded about it, and went with anything that caught their interest. The two of them have a motto, “The pioneers take the arrows”, meaning that if they were the first guy trying something, they knew that it may or may not work. Over a lot of years, these guys helped to define the reliable Corvair that we have today. In recent years their priorities have changed somewhat, and they have both distilled their own Corvair powered KRs to a configuration that they expect regular reliable service from. Today both planes are flying on 2,700 cc engines with Weseman bearings and our Front Starter System, seen here http://www.flycorvair.com/starterkit.html on FlyCorvair.com. You can check out our Corvair College #17 coverage at http://www.flycorvair.com/cc17.html and see pictures of each of their modern engines running for the first time on my run stand. If you’re a builder working today and would like to benefit from the decade of experience and 800 hours these guys have, consider building an engine that replicates the starter these guys are flying today.