I am going to run a series here called “Flying Planes.” We have an old section on our regular FlyCorvair.com Web site that covered the same topic, but it is out of date, and writing this series will bring it up to speed one story at a time.
With other types of aircraft, the plane itself is always the centerpiece of the story. With homebuilts, it is different. At the center of every homebuilding story is the builder himself. Looking at the plane can tell you a lot about the builder. You can get a good take on his workmanship, skills, taste in instrumentation, and creativity. Beyond these observable qualities, you can find out a lot more by getting to know a successful builder and asking why he chose a specific design, how he chose the Corvair, and how his previous experience plays into the aircraft he built. Besides being interesting, asking these questions and learning the answers is how new builders refine their own choices and make decisions on which path to proceed. Even if the answers you come to for your own project are not the same, they can still be honed by contrasting them with a successful builder.
Andy is an aviator of great experience, but his 601XL was his first venture into homebuilding. He holds a degree is aerospace engineering, a doctorate in engineering from MIT, and has several thousand hours of flight time, including a very long stint as a flight instructor in T-38 jets in the Air Force. He has taught as a professor at Embry Riddle Aeronautical University, and today is a full-time working engineer. You can comfortably say that the guy knows something about airplanes.
In our booth at Oshkosh 2011, I stand with three pilots who flew in their Corvair powered Zeniths. From left to right, Shane McDaniels who flew in a 2,700cc CH 650 from Missouri, Woody Harris in a 2,850cc CH 601B from California, and Andy Elliott in a 3,100cc CH 601B from Arizona.
I first met Andy at our 2002 Texas College. He was getting a good look at the Corvair, planning his next move in aviation. After our 601XL flew in 2004, Andy began thinking about the same aircraft, particularly a tailwheel plane like ours. Over time he chose a kit from Zenith and got to work on it. As he made progress, we spoke about Andy buying an engine from us. Our personal 601 had a 3100cc powerplant that I built to demonstrate some of the potential of the engine. It was assembled around a set of 140HP cylinder heads with their larger valves, and a very high compression ratio over 10.75 to 1. All of the systems on the aircraft are our standard Gold items, including the Front Starter System. The engine featured enlarged exhaust ports and very careful internal set up. On the dyno it exceeded 120hp, actually damaging the digital scale with the very strong power pulses from the high compression. Based on the internal changes and the displacement, I was fairly sure this was the most powerful non-turbo Corvair flying. We had it in the plane starting in the 2005 season, and racked up about 220 hours on it, including two trips to Oshkosh.
About the same time Andy needed an engine, another Corvair builder and friend of ours decided to make us an offer on our 601 airframe. A few phone calls and one Solomon like decision later, and our airframe was on a truck to Massachusetts, and we got the 3,100 ready to be shipped to Andy for installation on his 601 nearing completion. Before sending it, I pulled the engine down for inspection and out of general principle had the crank magnafluxed. It passed with flying colors, even though we had flown the aircraft very hard, and most importantly, it had not had a 5th bearing on it. The crank was just nitrided as was our standard practice in engine building. Although we could have sent the engine without the inspection, I thought it was well worth testing, because it had a fair amount of time on a very powerful engine. This was further confirmation to me that the nitriding was working. At the time, very few 3,100s had flow this amount of hours.
Andy likes to fly a lot, and once his plane was done he flew the test hours off in a very well thought out test program that reflected his professional background. We later had him document this and we printed it in our 2009 Flight Ops Manual. Over the months that followed, Andy built up time, a mixture of short flights in the southwest, and several trips to Oshkosh. In time he modified the airframe with small aerodynamic touches to increase its efficiency and control harmony. This included changing the elevator linkage and installing aileron spades. The engineers from Zenith were impressed enough with the aircraft to take the opportunity to fly it themselves at the west coast Zenith fly in.
Andy’s engine has made four separate trips to Oshkosh. Two under his ownership and two under ours. Pictured above in the 2005 Zenith booth Andy’s 3,100 makes its first Oshkosh appearance on the front of our aircraft.
The engine gave Andy steady service, which he credits to the certified MA3-SPA carb and an exclusive diet of 100LL fuel. (Other Corvairs can be set up for auto fuel, but the compression ratio of this engine makes auto fuel a non-option.) He was careful not to lean the engine at full power nor at low altitude, pointing out that the MA3 runs a very steady air fuel mixture under varying atmospheric conditions, so you don’t have to mess with the mixture if you don’t want to. Before heading to Oshkosh 2011, Andy had racked up 500+ hours on the engine (220 of these were under our ownership, 300 on Andy’s plane). I spoke to him about installing a Weseman 5th bearing on his aircraft, giving him the logic that if he was going to do it eventually, why not now? Although he had not built the engine himself and is not a mechanic, he found the installation straightforward with the tool kit and tech support provided by Jim and Rhonda Weseman. The installation was done over two weekends and the plane flew on to make an appearance at Oshkosh. It was selected to be the aircraft representing the Zodiac series at Aeroshell Square when the EAA presented the Aifetime Achievement Award to Chris Heintz.
Above, Andy’s aircraft at the EAA Chapter 1 Open House, Riverside, Calif.
Today Andy’s engine has more than 600 hours on it, 500 without a 5th bearing, 100+ with the Weseman bearing. He recently pulled the heads off and sent them to Mark Petz at FalconMachine.net for an upgrade to Mark’s specs. I originally had the heads done by SC Performance in California 10 years ago, and they were done to “state of the art” levels for Corvair auto racing guys. SC was a very well respected shop, but they didn’t use the types of seat alloys or valves that Falcon does. Mark inspected the heads carefully before reworking them, and was impressed at Andy’s careful operation; even with an extreme compression ratio the heads showed no signs of detonation. They were just losing compression through the old style exhaust seats. Andy ran the engine at high power settings, but Corvairs don’t have a real problem with this kind of work. Mark feels that considering Andy’s careful operation, the upgraded set of heads will go 1,500 hours. The bottom end of Andy’s engine showed no appreciable wear on the pistons or cylinders.
The upgrade to a 5th bearing and Falcon heads are not expensive modifications by aircraft standards. They each set Andy back about $1,000. You can ask any Rotax or Jabbaru owner if any upgrade on their engines costs this little. Combine this with an initial cost that was about 60% of either of the imports, and the engine still represents an excellent value.
In his travels Andy has met a lot of other builders at airshows, and people have written me privately many time to express how much they thought of the plane and the man. He has represented the Corvair movement in most of the western states, covering Copperstate, EAA chapter #1 Open House, the West Coast Zenith fly ins, and the Contact! alternative engine fly ins in Jean, NV. Additionally, Andy has used the aircraft to cover long trips to visit family and friends, including flights over the mountains in Colorado. He has a lot of praise for both the Zenith and the Corvair. What’s next for Andy? He is giving some serious thought to taking a step up in the speed and agility departments to a single seat Midget Mustang. The engine? The Corvair of course.
To read an updated on this story please click on this link:
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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.
Jeff Cochran, CH-750 builder from Alabama with a running 2,850 cc engine, writes:
Welcome back to the world wide web. You have been missed. Questions about the installation of your SS exhaust pipes. First, if ceramic coating of mild steel is bad, what about wraps on the SS system (except for the heat muff section)? Next, do the Heat Muff Box Ends need to be attached to the pipe and if so what is the best and worst method? And last, you say the pipes do not require tail pipe brackets, but the 601 Installation Manual calls for a steel tubing brace across the ends?
The new site is great, keep blogging.
Good to hear from you. The photo above is the first run of your engine at Corvair College #19.
Wrapping the pipes is bad for mild steel for the same reason why ceramic coating the outside of mild steel is bad: It keeps heat trapped in the steel, and mild steel can’t take this. If you look at the pictures of our Pietenpol in the late 90s at our http://www.flycorvair.com/carbice.html page, it had wrapped exhaust. I learned my lesson then. As a concept, it is worse than ceramic coating steel because when it cracks or disintegrates, you can’t see it. The only Corvair builder who I can think of who found this out the hard way was 601 builder and pilot Scott Laughlin. His wrapped mild steel exhaust gave in in about 100 hours, but he initially didn’t see it because it was wrapped. Wrapping the exhaust had its heyday in drag racing 25 years ago before coatings were available. Today they are a fashion statement on custom motorcycles. I can attest that it doesn’t work all that great either. My motorcycle, a Buell XB12X Ulysses came secondhand with a wrapped exhaust right where it passes my right thigh. It still radiates enough heat to be very uncomfortable. Sooner or later I am going to send the header pipes out to Jet Hott in Texas to have them ceramic coated inside and out. The best way to secure the heat muff ends it to get the box built and fitted right where you want it and then let a local welder put two tack welds on each end. The welds don’t have to be very big, two spots 1/4″ in diameter will do it. Other builders have used a hoseclamp above and below the box. Avoid anything that would puncture the main exhaust tube like a rivet or a screw. Your Zenith Installation Manual is an early one where we experimented with tying the ends of the pipes together aft of the nose gear. Subsequent experience has shown that this isn’t necessary.
This follow up came in from Gary Burdett, 750 builder from Illinois, also building up a 2,850 cc engine:
I take it that the short stubs are the place for the egt clamps.
If you’re planning on 6 egts, the stacks are the place to go. However, a majority of Zenith builders are using just 2 egts, one in each pipe, allowing them to monitor each side of the engine. In this case, they mount it about 6″ past the last stack.
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
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?
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 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.
Our Friend Rob Schaum, who is building a Murphy Rebel to be powered by a large Corvair, wrote us this note with a number of welding questions related to his quest to build his own motor mount. Rob bought one of our Motor Mount Trays and Spool Sets to get started, and then did some very impressive motor mount calculations that he ran past me. (His work turned out to be very well organized and accurate, best I have seen from a homebuilder.) His questions are far outside the simple scope of building a Corvair engine, but the engine by itself isn’t going to fly your plane. Unlike many people who market engines, I actually know how to mount them on planes. Over the years, I have seen a number of companies say things like “liability prevents us from commenting on that.” In many cases this is a face saving way of dealing with the fact that they sell imported engines, but don’t know any of the details of how you would do a custom installation. I have built more than 50 different Motor Mount designs for the Corvair, and I stand ready to help anyone with a question they may have with their installation, even if it is a one of a kind.
So I’m ready to start fitting tubes, as the motor mount jig is all ready to go and firmly attached to the work bench (see pic).
In preparation, I have read Finch’s book, and also L.S. Elzea’s WW2-era bible on aircraft welding. I am now all set up to start practicing on the “problems” at the back of the book (essentially practice exercises). I have to say, it’s a great book, and the “problems” do a great job describing techniques specific to specific steel tube structures and configurations. I expect that the most challenging parts to this will be joining the tubes to the heavy spools, due to the thicker spools sucking up all the heat. Also the 2-tube cluster (see above) might be challenging. I have some spool “stock” on hand to practice those specific welds, and plan to practice the exact cluster a few times before doing the real thing. Have a look at my set-up in the picture and let me know if there are obvious flaws. It is actually really sturdy front-to-back and laterally, but I am most suspicious of the twisting loads created while tacking-on the tubes. Some questions I had on the actual welding of the motor mount:
1) I can’t find any closeup photos of your 2-tube clusters at the lower firewall mount points. It definitely looks like the short tube is fitted first, followed by the long one, saddled primarily on the first tube due to the acute angle with the spool. However, I can’t determine whether the shorter tube is completely finish-welded before welding-on the longer tube, or if the shorter tube is tack-welded first, followed by the long one, then the cluster is welded as a unit (the latter appears to be standard practice in the literature). Can you please describe this procedure/area to me?
When you weld a cluster, it is not required to weld the parts of the cluster that are covered by the tubes placed later in the cluster. Basically, you are just welding the seams of the cluster that are visible on the outside of the completed joint. If you think about it, the forces on the joint are going to be transmitted through the outer surfaces of the tubes, and the welds that would be hidden inside would not be doing much work. I have cut apart a lot of welds in certified planes that have been around for decades, and none of the planes had the interior layers of the tubing clusters welded, even in the motor mounts or landing gears. Your assessment of the order of placing the tubes in the jig is correct.
2) Your motor mount 101 writings also refer to finger-straps on the 2 top tubes…do you still advocate that? I like the extra insurance at this location. Seems like one should have them on both ends (spool and tray).
Yes, they are a good idea. If you look at the November update on our website at www.FlyCorvair.com/hangar1111.html you can see photos of our personal Tailwind mount, and if you look closely, you will see that I put the tabs in where the upper tubes contact the tray. In our case, you have to remember that a Tailwind’s mount also has very high gear loads going through it. If you are an amateur gas welder, it can’t hurt to put the reinforcements in as outlined in our Conversion Manual ( available at the www.FlyCorvair.com/manual.html link). They are there to absorb tension loads on that joint. We do not use them on Mounts like our Zenith designs because I can get the full strength of the tube out of the joint by having it wrap slightly around the Tray at the contact point, and using 30 years of welding experience and a top of the line TIG welder to make our production Mounts. If this is your first mount, and you’re using gas, put them in. We don’t have them at the top as commonly because the top joint to the spools wraps around the spool, putting a lot more of the weld bead in shear, which is much less failure prone than a straight tension weld.
3) Is there an overall sequence to attaching the tubes to minimize distortions in the geometry due to weld-cooling stresses? Tack weld everything then finish weld? Or tack and finish each tube (or each matching set of tubes) then move on to the next set?
Tack weld everything then finish weld. To minimize distortion, work your way around the mount; it is good to do part of one cluster and then part of the next. There is no harm in this as long as you heat up and cool down the joint you’re welding each time. Something like 60 seconds leading in and 120 exiting in still air. Do not gas weld in a room that has air currents in it.
4) I had planned on tack-welding everything, then taking the thing off the wooden jig and test fitting on the plane. If all looked well, I was going use the tacked mount to construct a steel jig (I’ve been studying photos of yours), and do all the finish welding on the completed steel jig to avoid distortions that might otherwise occur using the wooden jig. Obviously, it would also enable better positioning of the work for the finish welding process. Is a tack-welded mount sufficiently strong to act as a “jig” for a jig, or will distortions generated during the construction of the jig end up “popping” tack welds on the mount itself?
If you are reasonably gentle with it, it will be fine. Try to put at least two tacks on each joint, but three is better. Try to space the tacks around the joint so they are not bunched up on one side. I would resist trying to gas weld a jig. It it is made out of strong enough material, it will be hard to get enough heat into it for welding without distorting the structure though warpage. If you have a buddy with a Mig or stick welder, burn the jig together using one of these techniques; they produce instantaneous heat which keeps distortion in check. Consider bolting your jig together. If you do weld it, pulling the tacked mount off it and checking it on the plane again isn’t a big step.
5) If I screw anything up, how structurally sound is it to cut the offending tubes off the tray, grind flat, and start over?
A lot of books act like this is a big deal, but it isn’t. If you couldn’t do it, then how would repairs be accomplished on steel tube planes? If you don’t like something, just cut the tube out, grind the weld bead away, and start again. The main thing that you want to avoid doing is running the flame set to an oxidizing flame (too much O2); this will BBQ the steel and it will take on a slightly rough, baked texture. If you keep going over a weld area with a flame like this, you are harming the base metal. Use good sense, and if you don’t like the way things are going, stop, take pictures and send them to me and we will figure it out.
6) Time permitting, are there useful weldments I should be attaching, or are Adel clamps the norm? What about attach points for the SS 1/8″ safety cable?
A safety cable can be threaded through the mount and bolted back onto itself, I would not weld tabs on for it. I would weld a battery ground cable strap onto the right rear corner of the tray; this will go to the back of the right hand cylinder head. Most of the other stuff will use adel clamps.
7) Much has been written about ambient temperatures for welding. How strict must one be in maintaining the ambient around 70 degrees, or can careful withdrawal of the flame compensate for virtually any environment? My garage is unheated, and it is currently 24 degrees F right now….perhaps I should do the finish welding in the basement?
In 1981 I was rabid about motorcycle drag racing. I lived in New Jersey, a state that regards drag racing as a birth right and a modern form of dueling. Englishtown was only 22 miles from my house, but like most young guys we were drawn to the “you can’t break the rules, we don’t have any” attitude of Atco, a track that was sanctioned by IDBA, the non-family entertainment version of the NHRA. That winter, my friend Ben and I welded up a new frame for our 830cc Kawasaki H-2. It had an all out Denco engine and in a fairly stock chassis had run 11.22 in the quarter. We were hoping that a new frame and an air shifter would get us in the 10’s at 120+mph. ( If you ride a 1,000cc Japanese sport bike that may not sound quick, but we are talking about an era where bikes handled like shopping carts with a bad wheel and a $29 Avon Speed Master II was considered a great tire because they usually stayed in the front rim when they went flat.) We welded up the frame using a gas torch in a 30 degree garage. When it was all done it looked as stout as the Pulaski Skyway. A dopey friend asked how we knew it wouldn’t break. I considered the question a serious insult. To demonstrate how strong it was I picked it up to chest height and dropped it on the floor in front of him. I was stunned that two of the welds had cracked! It was ugly to think about what might have happened if they had popped in the top end of the first run. No matter how you’re dressed, no one wants to think about how far you will slide at 100 mph on pavement.
Do not weld anything in a shop that is below 70F if you are building your own stuff for the first time. Pros can stretch this to a much cooler number, but it is a very bad idea to try to get away with this in your first go around. Find a warm spot and stack the deck in your favor.
The steel jig would go to you in the hope you’ll be able to save the next Rebelvair builder some time.
That is the kind of thinking that I have always found to be the best thing about the Corvair movement. I am glad to take the time to help any builder learn something, but it is especially rewarding when I can tell that the guy is already thinking of other builders who will follow him. Most other things you can do in aviation don’t have very much of this element anymore. It is unfortunate, but I recognize that I can’t change the commercial direction of aviation. The good thing is that I don’t need to, I am happy to just make our corner of Corvair power an oasis where builders who are here to learn, create and have fun have a place to be among friends.
Your help/wisdom here would be greatly appreciated.
You’re welcome, keep us posted on the progress.
Have a good night,
Mailbag is a collection of quick notes written in by builders, friends and readers.
“Looks great. About time!”
Rhonda Weseman, jsweseman.com, Corvair powered Fisher Celebrity now flying, pictured below
Thank you for the lovely words of encouragement. Yours was the first comment we got on this site.
“William and Grace,
“You guys did an awesome job. It’s only going to get better as time goes on and more content is added.”
Ken Pavlou, 601 XL 95% complete
We couldn’t have done it without you. Thank you for all your technical support. Thanks and kudos as well for running the online registrations for Corvair Colleges.
“Congrats on your new blog site. I much appreciated your advice on my Corvair conversion, and see this as a great asset for all of us neophytes trying to make a safe and reliable engine. Best wishes!”
Pete Kozachik, California, Pietenpol builder, CC #18 alumni
“Yes! This is great. Is there a date set for a C.C. at Roy’s In Michigan?”
We have not picked out a date for a College at Roy’s this year, but we had such a great time at Corvair College #20 last year that we are certain to have another event there. Check the Event tab on FlyCorvair.net for the latest.
“Nice to have you back. I am diligently building and showing steady progress.”
Terry Samsa, Minnesota, 701 builder, running engine at Corvair College #20
Thanks for the kind words. We thought we’d toss in the photo of your engine running at Corvair College #20.
“Great news William! And glad to see you back online…am personally looking forward to getting more great informaiton from you!”
We think this format is going to work out great for people really focused on making progress and hearing positive news from their fellow builders. Glad to have you following.
“Thanks Grace & William, this is what I have been waiting for, Just an update on my progress, as you know my engine is complete and waiting on an airframe, I purchased the wings kit for the Zenith 750 and have the left wing about 80% complete, my goal is to fly to a future College. Leaving the nay-sayers behind.”
“This is too cool, I flew in P.F. Becks Piet. at CC #19 and loved it, thanks for a great clip.”
Dan Glaze, 750 builder, alumni of Corvair Colleges #17-21
Thank you for the positive comments. The above photo is your engine when it fired up for the first time at CC #20. You and Albert are great assets for builders at Corvair Colleges. We look forward to seeing both of you again soon.
“Congratulations on the new site. I don’t tweet (or is it twit), Facebook, or friend, but I do enjoy the ability to access factual information from informed sources .”
Gary Burdett, Illinois, 2,850 cc powered, Zenith 750 builder, Corvair College #21 alumni
I’m not really into the social media stuff, and I don’t really know how all that stuff works. But I do know that this blog is working out well enough that I have to take back all the uninformed things I said about blogs in the past.
“It will be fun to watch this venue/resource mature. It looks like it will be a wonderful addition to the information hiway for the Vairhead community.”
Bob Pustell, 601XL/Corvair, still building, alumni of Corvair Colleges #13-17
Our pleasure. I was just telling some local F-4 guys the other day about my admiration for your Phantom experience. The above photo is you at Corvair College #14 in Massachusetts.
“Nice forum WW. It looks good from the iPad also. Getting closer to flight ready, I’ll be spinning the prop later this afternoon.”
Ron Lendon, Michigan, 601 XL, CC #17, 20
Good to hear from you. Keep your iPad handy. We intend to update this site frequently. From the archives, we brought out the picture of your engine running for the first time at Corvair College #17.
“1st test flight today. Ran hot but strong. Made some mods. Will try again tomorrow at dawn.”
Bob Lester, KR-2, Florida (Aircraft has been converted to new airfoils, Front Starter and Weseman bearing.)
Congratulations on getting back in the air. We’re looking forward to more updates on the performance of your aircraft. Please e-mail us a video when you get a chance. Grace and I picked out the above photo because it’s the first run of your updated Front Starter engine at Corvair College #17. 45 F and 150 mph wind chill. You look so toasty.
“Just found your new forum site. Hope all Corvair fans will log on to participate in and share the wealth of good information available here.
“We at Barnwell are rebuilding the storage room/bathroom in the big hangar where we hold the Corvair College. Also adding more overhead lights and will build two more work tables for this year’s event.
“I plan to be at Sun ‘n Fun and will again volunteer in the wood shop. If all goes well, we will likely be working on Pietenpol fuselages for John Godwin and Michael Oberlies.
“See you there.”
P. F. Beck, Pietenpol builder and pilot, Barnwell, S.C., host of Corvair Colleges #19 & 21
Thanks for the good words and the good news. We will again have a commercial booth at Sun ‘N Fun this year. It will be my 24th consecutive year at the event. We look forward to spending some time with you there. We drew out the photo above from our Corvair College #19 album. Grace took it from the front seat of your bird when you gave her a flight. Congratulations on flying more than 210 people and counting in your aircraft. Looking forward to another Barnwell College in the fall.
One of the most popular products we sell are Stainless Steel Exhausts for Corvair powered planes. We have been continuously making them since 2005. In this post we will cover the different systems that we make, talk a little about the pros and cons of certain designs, and look at some applications.
Prior to stainless, we built systems out of mild steel and had them ceramic coated. They looked great, but actually had a shorter life than plain painted steel. This is a surprise to many people, but here is why: Ceramic coating really works. It is a great heat barrier. A normal mild steel exhaust lives for a while as long as it can run cool. Ceramic coating the outside of it makes it look good, but it is actually hurting the system because it is trapping the heat in the metal. All affordable ceramic coating is done on the outside of parts. Very high end shops like Jet Hott charge several hundred dollars for a system because they use special tools to apply the coating on the inside of the pipes.
In 2003, I built an exhaust for our 601XL, N1777w. It was made from mild steel, but it was ceramic coated by the Moore Brothers, a very high end shop in Florida. The coating alone cost $300. It worked, and the best evidence of this was the fact that the heat muff for the carb didn’t work because the coating prevented any useful heat transfer. The system also racked up a lot of time on our plane, and it held up well. When other Zenith builders wanted to follow our success, I began to look at stainless as a better material for production exhaust systems.
Stainless is inherently a better material for exhausts because it is stronger at elevated temperatures and it is very resistant to corroding. Both of these are a big deal in aircraft because you can’t tolerate any kind of an exhaust leak in a plane. Everyone first thinks about carbon monoxide getting in the cabin, but my real concern is the possibility of starting a fire in the engine compartment. It is remote, but it is something that experienced aviators actually consider more of an emergency than having an engine quit on you. The strength and rust resistance of stainless, combined with good materials and welding techniques, applied to a design that has been flight proven not to resonate or crack on your airframe is the answer to minimizing your risk.
The stainless we use is an alloy called 304. It is the standard alloy of certified exhaust systems. The main tubes of our systems are bent for us by a shop in Florida that specializes in robotically bent tubing. They actually make the OEM systems for Lycoming and Continental, and make STC’d systems for companies like Powerflow. The head pipes on our systems are CNC machined from solid 304 bar stock. (They are made in the same shop in Florida that produces our Gold Prop hubs.) We have a separate shop that produces the Heat Muff Box Ends and another company that makes the tight radius front pipes. All of the systems are TIG welded in our hangar with 308L rod while they are pressure back purged with argon gas. Getting very expensive American made subcomponents from four different shops together in one jig and welded is something of a logistical challenge, but the end product is well worth the effort. In the past seven years we have produced about 250 Stainless Exhaust Systems for the fleet of Corvair powered planes. Chances are, most of the Corvair powered planes you have seen in person or seen in photos have a stainless Exhaust System that came out of our shop. Virtually every Corvair powered Zenith has an Exhaust System of ours on it.
To get a look at one of our Stainless Exhausts in action, watch this video of Jeff Moore’s Corvair powered Merlin on floats:
Jeff is from Newfoundland, Canada. His aircraft previously flew with a Rotax, but he has opted to repower his plane with a Corvair that he built with our conversion parts, http://www.flycorvair.com/products.html. His engine is a 2,700 cc 100 hp engine with all of our Gold Systems and a Weseman bearing. Jeff built his own mount utilizing one of our pre-welded trays. The Exhaust seen in the video is one of our Universal #2 Systems.
Below are three of the four production Stainless Exhausts we make. Universal #1 is the Exhaust System that is used on KR-2s and Cleanex airframes. Chris Smith’s “Son of Cleanex” was the first aircraft to fly with this system. The Universal #2 is the system that we make for aircraft like Jeff Moore’s Merlin. It fits a broad variety of planes like John Pitkin’s Kitfox 5 and Russ Mintkenbaugh’s Wagabond. It combines good motor mount clearance with the ability to work with a high thrust line. It is also a good match for a Pietenpol. Universal #3 is specifically bent for aircraft with a very low thrust line, like a Tailwind. Ordering information is on our Exhaust System page, http://www.flycorvair.com/uniexhaust.html
If you have any questions about which model is correct for your plane, just send an e-mail or give me a call on the shop line, (904) 529-0006.
Our fourth production system is our Zenith 601-650-750 System. This is specifically engineered to fit in the Zenith’s engine compartment, which has plenty of room, but the Exhaust has a sophisticated shape because it passes through the mount and clears the nose gear installation. This has proven to be the most popular system we sell. The Zenith has a particular motor mount geometry that requires this Exhaust to fit the engine correctly to the airframe. While some aircraft like Pietenpols utilize stock car exhaust manifolds, this is not an option on a Zenith because the car manifolds actually hit the upper tubes of the motor mount. Thus, a stainless system is an upgrade on a Piet, but a requirement on a Zenith.
One of the first things people ask about the systems is if they would make more power if they looked like aftermarket headers for cars. The magic answer is no. I tell them that you don’t have to take my word for it, you can just ask our Dynomometer. Before we came to the design we use, we tested lots of prototypes and systems. The technical reason why these compact systems do not restrict performance has to do with the camshaft pattern and the rpm range we use. The OT-10 cam has very little overlap, which is one of the reasons why it makes good torque. Engines like this, especially ones with 3,500 rpm power peaks, don’t see the same benefit from a full tubular exhaust system that a 7,000 rpm V-8 car with a high duration cam does. There are three basic goals served by making the most compact stainless system: First, it is lighter than something elaborate. Second, it is structurally stiffer, and therefore it is not prone to vibration damage (our Exhausts are cantilever off the bottom of the engine, they do not require tail pipe brackets nor secondary mounts). And last, it has a lot less surface area to radiate heat into the engine compartment. This last one is a bigger point than many people suspect. If you operate your aircraft in a very hot climate, this makes a difference on whether it is susceptible to vapor lock. I saw an experimental that had terrible trouble with vapor lock, yet when the builder looked in the engine compartment he missed the concept that his flat black mild steel tubular exhaust pipes were radiating the vast majority of the heat that was bothering his carb and gascolator. A poor exhaust system choice can easily put as much heat into the engine compartment as the engine itself. You are far better off having this heat run out the exhaust pipe. Stainless is a poor conductor of heat, and it does not radiate heat well. Combine this with a compact design, and you have the making of a cooler engine compartment.
The second most common question is about how loud the system is without mufflers. You can watch a number of videos, but they don’t give you a good feeling about the level of the sound. In person, most people are very impressed with the sound of the engine; throaty, but it doesn’t have a harsh bark. Some of the video shorts near hangars sound harsh because any aircraft turning a prop makes metal hangars resonate like steel drums, and microphones are very good at exaggerating this frequency. Out in the open, the engine is not loud. A subjective comparison; a Cessna C-172 in the pattern of your airport is a lot louder than a Corvair powered plane. It is also an effect of the engine’s cam timing; the low overlap means the cylinder is done burning by the time the exhaust valve opens. This short duration also has a secondary effect: Only one of the exhaust valves in each head are open at the same time. Each side of the exhaust system only has to serve one cylinder at a time, contributing to low back pressure. If you would like to use a muffler, you will end up with an exceptionally quiet aircraft. We flew our Pietenpol with a muffler for many years, and many people thought it was one of the quietest aircraft they had heard. Although many people think of quiet engines as being down on power, this is only true on engines that have a long duration camshaft design. Taking the muffler on or off our Piet only reduced the static rpm by 20-30 rpm.
On the subject of custom exhausts, I have produced a number of one-off designs for builders. Most of these were for engines equipped with 140 hp heads (they have a different size exhaust stack), or for a one-of-a kind airframe. If you find yourself heading in this direction, give me a call, and we will talk it over. It is also worth mentioning that we can install oxygen sensor bushings in the exhausts for builders who want to use an air/fuel meter. This is a concept with some appeal, but 90% of our builders still opt to use EGT probes, which are placed into the exhaust system after it is installed by drilling a small hole in the tubing.