Helicoil vs. Time Serts

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.


Balancer Installation

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.


The keyway on the balancer runs the full length of the hub.
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.

Custom Motor Mount Questions

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.

Hi William,

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.

Thanks, Rob

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?”

Peter B. Chmura


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!”
Garry Williams


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.


“Hey, William–

“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.

Stainless Steel Exhaust Systems


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.

Above, a pair of 304 stainless tubes before they are welded into the system. They are precision CNC machined; note the tapered surface to match the bevel on the Corvair exhaust gasket.

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.

Universal Exhaust Systems

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.

Two of the six stainless steel Clamps that we send out with each Exhaust System. They hold the Exhaust on the engine in the same way a traditional distributor clamp works.

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.

We send every Exhaust System with a pair of Heat Muff Box Ends. They make constructing the carb heat muff a piece of cake.

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.

Welcome to The FlyCorvair.net Blog


Welcome to the FlyCorvair Blog. With the help of a computer savvy friend, we have set this up to have a single point where people who are building and flying Corvairs can come and get fresh, factual information and motivation for their own projects. Most blogs are something of a monologue. This one will be different. For many years we ran a Daily Question and Answer section on our Web site. Hundreds of builders wrote in and had their question answered in this forum where other builders could also benefit. These posts are still archived on our Web site; they are a good resource, but we are taking a big step forward with this blog site.

Today we have access to vastly improved software and the answers can easily be enhanced with pictures and embedded video. I am pretty good at sharing information in the form of writing, but we all understand that in homebuilding, a picture is worth a thousand words, and a short video clip can often be illuminating and very motivational. This site also has other options that builders can choose, like being notified by e-mail when there is a fresh post here by clicking on RSS at right to subscribe for free. The program that we are using here is one of the most popular formats because it has very user friendly features like categorized archives right on the side of the main page. We are just getting to know the system, and we will make every effort to explain its features as we utilize them.

In 20 years of writing about aviation, all of my best efforts were sparked by a conversation or an experience shared by another aviator. Anyone reading this, no matter what your experience level, can be the builder who determines the subject of the next column. Just send your thoughts to WilliamTCA@aol.com, my regular e-mail address, or leave a reply in the comment box at the bottom of each post. Over the years, a number of Corvair aircraft discussion groups have sprung up on the Web, and almost all of them have faded away. One even had a name very close to our business, but had nothing to do with us. Another was nicknamed “The island of misfit toys” because it was populated by a lot of characters who had been tossed off other discussion groups. For many years, I was a major contributor to Mark Langford’s group, but we have mutually come to the friendly conclusion that I would be better off with my own place to converse with builders who choose to follow my testing and work. Mark wants to keep his group independent, and he believes that people should have a place to say nearly anything they wish. Inevitably I always try to steer the conversation back to what has been flight tested, what is known, what works for builders. These are divergent concepts, thus Grace and I have brought this site into operation. Although I will still write a number of articles for print publications, this blog and our main FlyCorvair.com Web site will be the only places where you will find me on the Web.

Just like you, I have an aircraft project out in the shop. Neither of us are going to get to the flightline if we spend all of our time at the computer. People are an equal element of flying to me. I love planes, but the human component drives me just as much. I work every year to strike a balance so that we make friends and finish planes. One without the other isn’t success for me. I have found that most builders feel the same way. I turned 49 last week. Statistically speaking, I have 26 more flying seasons left. Sounds like a lot, but I know right know that it isn’t enough. I can’t get more time, but I can spend what I will have wisely. It took me a long time to learn that I don’t have to like everything and everyone in aviation. I am not obligated to appreciate corporate jets nor $169K light sports. It took a while to understand that “the brotherhood of aviation” is a beautiful concept, just like Santa. Here is my reality: Aviation is a giant place, with plenty of room. All I am looking for is a place to build and flight test our ideas, share them with friends and the time to go do some flying. I didn’t get into this to make everyone into an alternative engine convert, nor is it my job to tolerate every mystery e-mail name with an opinion and a keyboard. Staying focused on spending my time wisely brings me to the decision to put our effort into the people who will read this site.

Here, by choice, we can have a positive discussion between real people who have come to learn and share information on our favorite engine. It isn’t going to be for everyone, but I do have a very long track record of working with a great variety of people. These builders have possessed the common goals of succeeding in aviation and sharing this with other builders. Sounds pretty basic, and for most builders it’s just common sense, but it is worth noting that there is 25 times as much information on aircraft building on the Web today as there was 10 years ago, yet the completion rate of aircraft has not changed, and the accident rate may be slightly higher. Quantity of information isn’t a substitute for quality, and is often just more hay when you need to find a needle in the stack. Together we can make this the location for flight proven information and friendly motivation. Welcome aboard.

Thank you.

William Wynne


Corvair College #22, March 9-11, 2012 in Austin, Texas


We are 2 months away from the next Corvair College. CC #22 will be March 9, 10 and 11, 2012, at KGTU Georgetown Municipal Airport in Austin,Texas. This College will be hosted by Kevin Purtee and Shelley Tomino.

Both Kevin and Shelley are well known and respected in the Pietenpol community. Kevin finished his Corvair powered Pietenpol in 2009, and has flown it extensively, including two trips to the Pietenpol Reunion in Brodhead, Wisc. Get a look at this video of the aircraft’s first flight:

One of the things I look for in a College host is a person with a positive outlook and can-do attitude. Kevin worked on this aircraft for 16 years before it flew. His story is an outstanding example of positive persistence. The success of your own project largely depends on 3 factors: if you can afford it, from whom you get your advice and motivation, and whether you develop the personal persistence to see it through. Corvair College#22 will be an outstanding opportunity for you to address all three in one setting.

If you have not been to one of my previous Colleges, take the time to read about any of our Colleges from this section of our Web site: http://flycorvair.com/cc21.html

College #22 will be run just like previous events where the primary focus is on the progress you will make on your own engine. After 12 years of Colleges with hundreds of builders in attendance you can find countless stories of the value of attending a college, told by builders just like you.

As you read the notes, picture yourself immersed in #22 in Austin. If you have not made the progress you planned in the past year, change your approach, sign up for this event, and take a positive step in starting this year off with a plan. Attending a College is the #1 cited milestone mentioned by people who are out flying their own Corvair powered planes today. Don’t wait to see if this year will be different: Make it different.

Corvair/601 builder Ken Pavlou, aka The Central Scrutinizer, has set up the online registration for #22. Ken has covered this on 6 of the previous 8 Colleges from his workshop in Connecticut. Here is the direct link to the registration page:


We will be continuously sharing more information on the College in the coming weeks. If you have a specific question, feel free to e-mail it in or leave a comment at the bottom of this post and we will gladly cover it.

Thank you,

William Wynne