Corvair engines

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Doran Jaffas

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Hello everybody out there in aviation land. Been a while since I posted or asked a question and there may be answers to this but I just haven't seen them so I'm going to put it out there again and please forgive the repeat if it is. I'm looking at an aircraft that has 110 horsepower Corvair engine. I am curious as I have not been able to find any solid information and I probably just haven't looked in the right place or places but again I am curious if anybody knows suggested TBO on 110 horsepower and what the minimum compression would be? Aircraft I'm looking at does not have the fifth bearing but that really doesn't concern me at this point and it has a slide valve carburetor mounted on the top that I haven't seen before. I mean that type of mounting for the slide valve. the engine itself is flown about 350 hours but it's not flown in quite some time so again I'm asking the question and sorry for the rambling here.. what would the minimum compression be on this engine and suggested tbo's?

Thank you folks and looking for your answers.

Doran Jaffas
 

Doran Jaffas

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I just hit the search tool with "Corvair" and got 10 pages of hits within hba.
Okay, I guess that shows my one track mind of asking folks on here. Thanks for that info I will do the same. I specifically looking for acceptable compressions and TBO is regarding the aircraft conversions.
 

mcrae0104

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The short answer is that normal compression is 72/80 or better, but for more context (on this specific question and on general philosophy of the engine) I would strongly suggest reading the FlyCorvair Maintenance, Operation, and Procedures Manual.

As you probably know, as with any experimental engine, there is no prescribed TBO, although I believe I have heard 1,000 hrs suggested. @Daleandee, who operates a Corvair-powered Sonex, might be able to offer some more experience-based perspective on TBO.

Personally, I would not fly with a slide carb mounted above the engine (dripping gas above an engine is no bueno), and using a fifth bearing is considered mandatory these days, even on a Piet. A search on FlyCorvair.net should hit on both of these subjects. If I were considering this engine, I’d ask the builder for an inventory of the parts (and mfrs) used to build it, and set aside some time and money to make sure it conforms to current standards. The Corvair Conversion Manual (same link as above) defines these standards.

Some of the things to consider (at least those that come to mind at the moment) would include:
  • Adequate, aviation-quality fuel delivery system?
  • Timing set correctly for aviation application?
  • Ignition system: I’m guessing this is not a WW points + elec. distributor with switching between systems?
  • Correct spark plugs?
  • Good quality, forged pistons?
  • Crank: factory nitrided, or if machined, nitrided and proper fillets at journals?
  • Heads: exhaust valve rotators installed? Appropriate rocker arms (if not original)?
  • Adequate oil cooling system?
  • Adequate baffling system?
  • Appropriate starter and alternator system?
  • Appropriate prop hub setup?
 
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Doran Jaffas

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You answered my questions. I flown behind several different types of engines but not the corvair. This airplane looks really nice even though it is set for a while but the engine configuration calls it into question even though it has 350 hours on it. I have told the prospective seller that I need to see at least a video of the engine running recently before I would proceed with this transaction. I've never heard of an updraft carburetor being mounted on the top of an engine before so I would not even be sure how the fuel would be delivered without a fuel pump misting it into the Venturi somehow. Again though with 350 hours on it it obviously ran on this particular Pietenpol.

Still though I have questions about it and at this point unless I get sent a video of it running and running really well I think I'm going to pass and consider the money spent on the inspection the cheap insurance policy for not spending more although nobody likes to give money away these days. I have a Tailwind W10-8 that is a really nice airplane to fly so I may just put a a few thousand into this to really bring it up to like new specs including possibly a new paint job although it doesn't look bad the way it is. Anybody out there, I'm looking for something along the lines of a two place shorter field performing that does not have to have rocket performance just to compliment what I have and fly right now. Thanks for the answers everyone I really appreciate it.
 

Daleandee

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I believe mcrae0104 has answered as well as can be said. How much life you get from these engines (any engine) depends on the build quality, the maintenance given, and the way it is operated. The values I was given that are said to be conservative were 1000 hours on the heads and 1500 for the engine but the caveat is that it must be maintained to a standard and certain procedures must be followed as well as certain products being used.

In the case of what you have said (and what little is known) I'd be very wary. No reputable Corvair engine builder that I know would ever recommend a top mounted carb in an airplane installation. I also don't know of any Corvair builder worth their salt that would build an engine without a 5th bearing on it unless it was built more than 15 years ago.

And for a personal note ... slide carbs are absolutely verboten on anything that I'm going to be flying.

Just out of curiosity ... who was the engine builder? Where did he get the parts to assemble the engine? Where's the flywheel located? What kind of ignition system is installed? The carb being top mounted means someone had to design and custom make an intake for it. How did that come about, and was it tested for efficiency?

Dunno if this helps ...
 

BJC

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The values I was given that are said to be conservative were 1000 hours on the heads and 1500 for the engine but the caveat is that it must be maintained to a standard and certain procedures must be followed as well as certain products being used.
1000 hours is high time for a homebuilt.


BJC
 

TFF

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I imagine that that is an original Corvair conversion long before it was an industry. The Bernie was the first I believe.
 

Daleandee

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The Bernie was the first I believe.
Yes sir ... at least that's the way I understand it. He put one on a Pietenpol in 1960. I understand it still had the factory belt driven cooling fan setup ...
 

Daleandee

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1000 hours is high time for a homebuilt.
Yes it is. I believe the heads will likely go that far but I do suspect that a freshen up will need to be done in the 500 hour range. That'll be about the same time I pull the dual ignition distributor and return it for a rebuild ...
 

Doran Jaffas

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I believe mcrae0104 has answered as well as can be said. How much life you get from these engines (any engine) depends on the build quality, the maintenance given, and the way it is operated. The values I was given that are said to be conservative were 1000 hours on the heads and 1500 for the engine but the caveat is that it must be maintained to a standard and certain procedures must be followed as well as certain products being used.

In the case of what you have said (and what little is known) I'd be very wary. No reputable Corvair engine builder that I know would ever recommend a top mounted carb in an airplane installation. I also don't know of any Corvair builder worth their salt that would build an engine without a 5th bearing on it unless it was built more than 15 years ago.

And for a personal note ... slide carbs are absolutely verboten on anything that I'm going to be flying.

Just out of curiosity ... who was the engine builder? Where did he get the parts to assemble the engine? Where's the flywheel located? What kind of ignition system is installed? The carb being top mounted means someone had to design and custom make an intake for it. How did that come about, and was it tested for efficiency?

Dunno if this helps ...
Thanks for the reply. as far as the slide valve carburetor goes I have used a couple successfully on home builts when they were mounted underneath the engine. There is a specific starting sequence that must be adhered to but once you get the needle tuned in they started easily and the fact that they are less prone to carburetor ice than a normal float carburetor I actually found them to work very well. Although I never flew above 7,500 ft so never really felt like I had the need to lean. Some of the slide valve carburetors do have mixer control of A sort and those also have worked very well. My standard of operation would be a marvel schebler or something along that line.
The aircraft was built in the mid 80s so that answers the question about the time frame. It does have 350 or so hours on it but not any time on it within the last several years. Attached is the picture of the engine that I was sent. I do not know the build or where the parts came from. I do know back then the fifth bearing was not added as a general rule and many of them flew successfully. Obviously having the fifth bearing installed is a good idea just for the extra security on the loads at the engine and crank are undertaking. I appreciate your comments. I hope the picture helps. I have told them that until the engine is running that I will not pursue the purchase of this aircraft any further. reason being is I don't want to remove the wings and take it home on a trailer and have another project right now. That being said if the deal doesn't go through I will just put several thousand dollars into my Tailwind to add a new paint job into thoroughly go over a few things whether they need it or not.

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patrickrio

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If I remember right, the early Corvair conversions like this one were usually pretty low power compared to modern conversions. Think as low as 65-70 HP..... That means lighter prop and hub too. The normal VW conversions of the time were also generally getting lower HP than modern VW conversions.

The result of the lower HP and lighter prop and hub though is that flying without the modern 5th bearing was less likely to cause failure AND the engine, while it might not last as long as the modern 5th bearing conversions do now, did last quite a while.

The 5th bearing "revolution" really happened because a few intrepid Corvair builders were doing builds that pushed HP up into the 130-140 HP range and the engines started having low hour crank failures (Mark Langford was one of these Corvair innovators that had in flight failures that he luckily landed safely).

The process of pushing the envelope is how you find weaknesses. This particular weakness has a good solution that really reduces the likelihood of a failure that can be particularly deadly because it is SURE to stop the engine and usually happens during the most dangerous of take off conditions.

But the truth is, If you are flying a low HP engine build without a 5th bearing, in an airplane that generally flies slower and is more forgiving because it works with that lower HP, you are not taking the big risks that the high HP engines put in high speed airframes were taking.
 
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Doran Jaffas

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If I remember right, the early Corvair conversions like this one were usually pretty low power too compared to modern conversions. Think as low as 65-70 HP..... That means lighter prop and hub too. The normal VW conversions of the time were also generally getting lower HP than modern VW conversions.

The result of the lower HP and lighter prop and hub though is that flying without the modern 5th bearing was less likely to cause failure AND the engine, while it might not last as long as the modern 5th bearing conversions do now, did last quite a while.
I appreciate the reply. I told the individual selling this airplane I need to see a video of it running before I proceed further with the transaction. I sent him what I thought would be a reasonable startup checklist. A picture of the engine follows. I was told it was rated at 110 horse but I think that's stretching it. I like your version of it better lol.
 

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patrickrio

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I appreciate the reply. I told the individual selling this airplane I need to see a video of it running before I proceed further with the transaction. I sent him what I thought would be a reasonable startup checklist. A picture of the engine follows. I was told it was rated at 110 horse but I think that's stretching it. I like your version of it better lol.
well, It COULD have 110 hp.... It may have had some piecemeal "improvements" done that start moving it into the danger zone for crank failures...... That is what you need to look for actually. The more desirable situation in this case is that the seller is exaggerating the output HP substantially. Looking at build components like cams, carbs, heads, pistons, and ignition systems from one side and then look at the flight characteristics of that particular airplane compared to other known engines in the same airframe. This will give you a clue to actual HP.

Also look for a more modern crank preparation as that is a substantial improvement in the weak point. Stage one is a nitrided crank from an original turbo Corvair engine. Stage 2 is a modern forged crank, Stage 3 is a billet crank. All should be verified for proper balancing. receipts held by the owner for such items can give you some piece of mind. Having any of these balanced options from a reputable crank source can make even a true 110 HP a reasonable engine I think.

But I think that 110 HP Corvair flight engines and flight parts were not really a thing until the late 90s/early00s. If you have low RPM HP increasing parts on that engine from that era without the improved cranks of the time, that is what you need to be careful of.

If the engine is bone stock mechanically, without having been bored and stroked or anything, it can't make 110HP at flight engine RPMs. That is what you hope for. Or a FULL conversion to higher HP with a verified improved crank.
 
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TFF

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In a Corvair it was 110 hp. In airplane form it’s about 65. The original Corvair conversions were A-65 replacements not O-200. People kept pushing the horsepower up and up requiring the fifth bearing.
 

patrickrio

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Also, I have been editing my comments, likely after you read them..... you should go back and re read them as they have better info now.
 

Pops

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In a Corvair it was 110 hp. In airplane form it’s about 65. The original Corvair conversions were A-65 replacements not O-200. People kept pushing the horsepower up and up requiring the fifth bearing.
True-- Old friend of mine built a Piet with a Corvair engine back in the 1970's and he said it was producing about 65hp.
 
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mcrae0104

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Based on what we’re seeing in the photo, I’d steer clear of this engine unless the plan is to bring it up to present standards (i.e. disassemble & rebuild). Yes, it has worked for some amount of time, but my #1 goal would be to have an engine that is as reliable as possible. A lot has been done in the last 35 years in this regard, and I would take advantage of every bit of this that I could.
  • Prop hub - looks like a one-off. Might be OK, but it’s an unknown. Is the material appropriate, does it use a proper safety shaft, etc.?
  • Starter, ring gear, harmonic balancer - another unknown (hidden by the baffling). There has been some debate over the years about the best setup, but I prefer the front starter & retaining the harmonic balancer in the rear (perhaps the most proven setup in terms of hours).
  • Crankshaft - unknown
  • Cam & cam gear attachment - unknown
  • Charging system - unknown
  • Ignition system - unknown
  • Oil cooling system - unknown, perhaps stock?
  • Carb & intake manifold - again, looks like a one-off. I’d lose that heavy top cover/fan bearing. Carb belongs on bottom, especially for a slide carb. Welded-on manifold pipes are preferred to bolted flanges.
For me, there are too many unknowns but it could be a good core for rebuilding (YMMV).

On the topic of power, a stock 110hp engine would make about 80-95hp at flight RPM range (when new). See GM chart below (from Mark Langford’s excellent Corvair page). Engines that make more power do so through some combination of a different cam and increased displacement (overbored stock cylinders, larger VW cylinders, and/or stroked crank). I don’t know what Bernard Pietenpol got out of his engine, but I suspect he wouldn’t have bothered for a mere 65 hp, given the weight of a Corvair compared to an A-65 or VW.

1624543053178.jpeg
 
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patrickrio

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Pretty sure Pietenpol chose the engine because it was really cheap and the weight/hp was great compared to the 40HP Ford model A that was used on most of the early AirCampers.

He was taking an essentially stock engine complete with original cooling fan and doing minimal modifications necessary to attach a propeller that turned about 2800rpm. His goal was CHEAP and more than 40 HP at a better weight than the model A engine. Smooth running 6 cylinders and flat boxer like real airplane engine format were just a bonus.

Because of Ralph Nader and "Unsafe at Any Speed" Corvair engines were very available for really cheap starting in the late 60s. Pretty much nobody wanted that car anymore so junkyards were practically giving the engines away.

The Volkswagen Beetle engines were more expensive and required more mods for more money during this time to make more than 40hp at 2800rpm.
 
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