Year: 2012

Friends,

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.

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.

 William

To read an updated on this story please click on this link:

Chinese Crankshafts for Corvairs, update 2/17/13. 

If  the pictures on this story are small, try clicking on the F5 key at the top of your keyboard.

Friends,

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.

William

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

Thank you.

William

Matthew Lockwood writes:

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?

Matthew,

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.

William

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.

Carl:

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 above photo 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.

 

William