Corvair conversion engines

Richard Lamb wrote:

Cal Vanize wrote:


The issue us addressed in this page:

http://www.flycorvair.com/crankissues.html

The date on the page is 15 January 2006 - just released information.



Ron Webb wrote:

Do you have a link for the broken cranks? I cannot find anything
about broken cranks on the "Corvair authority" site.

http://www.flycorvair.com/

I did find the following statement:

"I have never seen a cracked head, cylinder, case, crank or rod in
the hundreds of Corvair engines I have inspected. It is a very strong
engine."

The Corvair engine has been flying since the early 1960's. Seems odd
that ANY flaw would only now be being discovered.





that dose seem like a lot of broken cranks...

Three out of five cranks cracked. All with 200 or less hours. That's a
small sampling, but not very good results.

The article does indicate that the cranks were from engines in planes
that were flying. That's the good news. But does that also mean that
the engines need a teardown and inspection as part of every oil change?

"Cal Vanize" wrote

The article does indicate that the cranks were from engines in planes that
were flying. That's the good news. But does that also mean that the
engines need a teardown and inspection as part of every oil change?

If you are running a conversion that is different from William's
conversions, it could be a good idea. g

If people take the time (yeah, lots of it) to read the whole article, you
will notice a few things, and I will attempt to point out some of the more
significant (to me) points.

Biggest point. Do not use corvair engines outside of the recommended
operating parameters. Some sub points.

Biggest one, don't use longer prop extensions. Big time no-no.

Others include, don't use heavy props, or hand carved props. Don't
overstress the prop with some aerobatic maneuvers, or hard landings. Make
sure the crank is properly ground. Oil systems must provide for consistent
oil flow to all parts, at all times; stay away from two line cooler and
filter systems. Use low RPMs and big props, rather than smaller props and
higher RPMs. Avoid detonation, which is easy to let happen, if treated like
an aircraft engine.

Obey all points of his conversion manual. Nitrated cranks are a good way to
add an extra margin of safety, when obeying the conversion manual, but the
other examples that have followed the manual have been OK for long
operational periods, even without the nitrated cranks.

Avoid other's add ons, like extra bearing hubs, as they have not been
tested.

I am sure I missed some points, or miss stated some, but if you are using
corvair power, it would be wise to investigate what this man has to say, and
not take my word on it.

I remember saying a long time ago, that I would feel better (or something
like that) if a redrive was used to take the stress off of the crank. I
think I will still stand by those words. Of course, It would need to be a
properly researched and tested redrive, which at this time, does not exist.
--
Jim in NC

On Wed, 18 Jan 2006 19:17:35 -0600, Cal Vanize
wrote:



Richard Lamb wrote:

Cal Vanize wrote:


The issue us addressed in this page:

http://www.flycorvair.com/crankissues.html

The date on the page is 15 January 2006 - just released information.



Ron Webb wrote:

Do you have a link for the broken cranks? I cannot find anything
about broken cranks on the "Corvair authority" site.

http://www.flycorvair.com/

I did find the following statement:

"I have never seen a cracked head, cylinder, case, crank or rod in
the hundreds of Corvair engines I have inspected. It is a very strong
engine."

The Corvair engine has been flying since the early 1960's. Seems odd
that ANY flaw would only now be being discovered.





that dose seem like a lot of broken cranks...

Three out of five cranks cracked. All with 200 or less hours. That's a
small sampling, but not very good results.

The article does indicate that the cranks were from engines in planes
that were flying. That's the good news. But does that also mean that
the engines need a teardown and inspection as part of every oil change?


These were also 40 year old cranks of unknown provenence, pulled out
of old car engines that may have been thrashed to within an inch of
their lives in previous "inCARnations"

Let's say you have to replace the engine 4 times to get 2000 hours. You are
still saving money over the cost of a Lyc or Cont and there is no guarantee
they will make it to TBO either.



"Cal Vanize" wrote in message
...

As my research continues, I have been investigating possible engines for a
601XL. The Corvair engines looked like a good candidate. The reports
seemed very good and the engine was surprisingly inexpensive for initial
purchase and long-term maintenance.

The stated expected TBO is 1500 hours and the Corvair Authority website
documents the use of a Corvair engine in a 601XL.

Everything seemed OK until yesterday when I read the most recent updates
on their website. Seems that the "untreated" automotive cranks have been
cracking in a very short time. Nitriding seems like the only solution.
But with standard cranks cracking at under 100 hours, what would be the
expected life of a nitrided crank. Twice as long, four times as long,
eight times as long? This would still fall short of the 1500 hour TBO
stated by the Corvair Authority.

Does anyone have any first hand experience with Corvair conversion
engines? Any info on their realistic life and reliability?

TIA,

CV

But would you have to replace the engine?
Maybe just a crank overhaul every 4-500 hours, in the middle of
winter, after a good snow storm, nothing else to do.

I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically
designed for this in the first palce. Maybe a good redrive and flywheel
would be a better way to go?

"Bret Ludwig" wrote in message
oups.com...

I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically
designed for this in the first palce. Maybe a good redrive and flywheel
would be a better way to go?

That is my opinion, also.
--
Jim in NC

When it really gets down to facts, most often aircraft engines really
don't cost any more than auto conversions and the aircraft engine
appears to be more reliable.
No redrives needed, redundant ignition and lots of other things that
makes them better.

I was a firm believer in auto engine conversions but i haven't seen many
last a long time except for the Subaru and Rotax engines.



Morgans wrote:

"Bret Ludwig" wrote in message
oups.com...


I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically
designed for this in the first palce. Maybe a good redrive and flywheel
would be a better way to go?


That is my opinion, also.

I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically
designed for this in the first palce. Maybe a good redrive and flywheel
would be a better way to go?

That is my opinion, also.
--
I partially agree.

I agree that hanging a prop directly on the end of an automotive crank, even
if you put it on the flywheel end, is a recipe for a short tbo even at low
power and for a high failure rate at high power. (If you only use it to
push an airboat around the local swamp, you can keep a couple of bottles of
skin-so-soft in your tackle box.)

However, switching to a traditional aircraft powerplant may not solve the
problem. You really only have the full value of testing, experience, and
service history when you mate an unmodified engine to an airworthy propeller
with which that engine was certified--and preferrably in a combination used
by a large number of aircraft in regular service for a reasonably long time.
Remember the crankshaft problems in some of the Cessna 172's soon after the
change from the Continental O-300 to the Lycoming O-320. (I think it was an
early 160HP version, but have long forgotter the dash number--and the
problem was promptly solved.) There have been other "teething" problems as
well on various engines...

In the special case of a KR-2, which was the subject of at lease two of the
Corvair engines torn down and inspected, the plane sits too low to swing a
70+ inch diameter propeller; and IIRC was originally designed for VW engines
swnging 52 inch diameter propellers. I have heard that the KR-2S sits
enough higher to accept a larger prop, possibly 60 inch diameter. That
seems to negate the reduction drives, although a shaft drive, similar to the
one Steve Whittman developed for his V8 powered Tailwind, could be
interesting. BTW, the plans are still available--I think Aircraft Spruce
still sells them. Also, Revmaster (and possibly others) offers an aircraft
engine based loosly on the VW dimensions and a Jabiru could work--especially
with a 3 blade prop...

On Thu, 19 Jan 2006 15:35:13 -0500, "Morgans"
wrote:


"Bret Ludwig" wrote in message
roups.com...

I just think hanging a prop on a crank directly is a non-starter in
the first place...especially on a crank and case not specifically
designed for this in the first palce. Maybe a good redrive and flywheel
would be a better way to go?

That is my opinion, also.

What isn't there can't break. That's my reson for a direct drive 'vair
insted of a geared Soob - same weight - same HP.