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n282rs(at)earthlink.net
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 Posted: Fri Jul 07, 2006 12:19 pm Post subject: Corvair cranks |
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William Wynne's own crank had stress fractures in it. This was a standard
conversion. I'm sure that's what convinced him to recommend nitriding the
cranks. I did not have a prop extension, or horsepower upgrade and yet my
crank broke. My crank had not been nitrided either, but then I had never
heard of a crank failure on a Corvair until about a year or so ago. I
figured since they have been flying Corvairs on Peitenpols since the 60's,
I didn't see any rush. Since my crank break, I have come to realize that we
have been flying these engines much harder than the Pietenpol guys do.
Possible reasons for my crank break:
Case being "sloppy". I wish I had the measuring equipment to verify this
one way or another.
Prop out of balance. Maybe. I know I'm going to get it dynamically
balanced when I get it flying again.
Max performance takeoffs. Nearly every flight began that way.
Cruising at 3100 rpm or higher. I almost always pushed the engine hard. I
think WW usually cruises at 2900 rpm.
I'm not completely convinced about the nitriding, because it is a hardening
process. If one where to pose the question of whether or not to substitute
grade 8 bolts for AN bolts, the argument would normally be that grade 8
have been hardened and are more brittle than an AN bolt . It would not be
able to take the bending moment that an AN bolt could. For some reason it
must be different on a crankshaft, but I don't understand why. However,
since the experts have determined that nitriding is the way to go, I will
follow.
Something we all need to do regardless of the engine we fly behind: When
you hear of a crash, engine failure, or other incident, play the scenario
out in your mind. Maybe even while sitting in the cockpit. Plan what you
could do to survive the situation. Look at your plane and see if you need
to change something to keep the same problem from occurring to you. Maybe
inspect the parts that may have contributed to the incident.
Randy Stout
n282rs"at"earthlink.net
www.geocities.com/r5t0ut21
| Quote: | [Original Message]
From: Tom Farin <tfarin(at)farin.com>
To: <zenith-list(at)matronics.com>
Date: 7/7/2006 8:34:40 AM
Subject: RE: Zenith-List Digest: 78 Msgs - 07/06/06
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| Quote: |
The most widely talked about issue relating to Corvair engines in the
last two years is the four recent crank failures. Keep in mind the Corvair
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engine has been flying in aircraft since the Corvair was introduced in
1960. There was a tremendous amount of dicussion at Corvaircraft, on
William Wynne's site, and at Mark Langsford's site. Mark had one of the
four failures. The consensus seems to be that in all four cases the
installation deviated from the instructions in Wynne's manual - prop
extensions, horsepower upgrades, etc. - in a way that placed additional
stress on the crank. In spite of that both Mark and William put
substantial time into examining the causes of the failures. In spite of
the fact there are no known crank failures on installations per the WW
manual, WW is now recommending the crank be Nitrided to give it additional
strength. In spite of a harrowing experience, Mark is again flying with a
stock WW conversion.
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JAPhillipsGA(at)aol.com
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| Posted: Fri Jul 07, 2006 12:29 pm Post subject: Corvair cranks |
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Install a different engine ? Just had to do it. I don't know what got into me. I cam only blame global warming, sun spots, green Scotchbite and huffing zinc chromate
do not archive
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randy(at)shadycreekoutlaw
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| Posted: Fri Jul 07, 2006 5:16 pm Post subject: Corvair cranks |
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I'm not so sure that nitriding will eliminate...or even help the Corvair
crank breaking problem...
I'm not an expert on nitriding, but I've been around it a little in my
time... I used to machine plastic ejection molds and tooling dies... There
are what's called "ejector pins" that the tops of mold and dies slide up and
down on to make the 2 halves meet properly...
If you can imagine a 4 legged table sitting on it's top with the 4 legs in
the air, then cut a piece of plywood with 4 holes in it to fit over the legs
and slide up and down, this is what it's equivalent to... The legs would be
the ejector pins. (I've attached a picture of a MUD Die) We used to have
these pins nitrided all the time... Nitriding, at least what the nitriders
told me, is that it doesn't make the part more resistant to breakage, but it
makes it tougher from a wear perspective... I know on molds and dies, the
top half sliding up and down through every cycle on the ejector pins, they
would wear, then the 2 halves wouldn't match up right...they'd mis-match...
We'd nitride these pins to make their outer surface harder to resist
wear...they'd still break as easily as they were before nitriding, if side
load was applied, their outter surface just didn't wear as fast... You can
hit a nitrided part with a file and the file will just bounce off it...but
keep on filing, and in a few thousandths, you'll be through the nitriding
and the steel will be soft as ever... SO,
from my limited experience and knowledge of nitriding, if I was having a
crankshaft that was wearing out quickly on the bearing journals, nitriding
seems like a good cure..but to use as a cure for breakage from side load, it
just doesn't make sense to me... In my thinking, you'd need a flange and a
thrust bearing to handle side loads... Anyone out there care to elaborate
more on nitriding??
Maybe I'm way off base here... Don't know... I will say that at this time I
plan on using a WW Corvair conversion in my XL when the time comes... Good
lord, I'm just working on the wings right now! 
Just my .02 worth...
Randy
XL Wings - Plans Only
http://www.n344rb.com
Do Not Archive
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pmaxpmax(at)HOTMAIL.COM
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| Posted: Fri Jul 07, 2006 6:06 pm Post subject: Corvair cranks |
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There should be many hundreds of hours of nitrided crank testing happening
in 2006 and 2007. Just sit tight and we'll do all the test flying and keep
you informed.
This subject has been beaten to death on the Corvaircraft list. Search the
archives to your heart's content. I'll be test flying my nitrided crank
while you do!
Phil Maxson
601XL/Corvair
Northwest New Jersey
Oshkosh Bound in a couple weeks.
| Quote: | From: "Randy Bryant" <randy(at)shadycreekoutlaws.com>
Reply-To: zenith-list(at)matronics.com
To: <zenith-list(at)matronics.com>
Subject: Re: Corvair cranks
Date: Fri, 7 Jul 2006 21:11:08 -0400
I'm not so sure that nitriding will eliminate...or even help the Corvair
crank breaking problem...
<<SNIP>>
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Kevin Bonds
Joined: 09 Jan 2006
Posts: 171
Location: Nashville, Tn
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| Posted: Fri Jul 07, 2006 8:07 pm Post subject: Corvair cranks |
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Randy
Check out Mark Langford's site here:
http://home.hiwaay.net/~langford/corvair/flexplate/problem.html
He broke his crank and did a lot of the legwork into finding out why and
finding the Nitride solution.
Kevin Bonds
Nashville TN
<html><image
src="http://home.comcast.net/~kevinbonds/images/Empennage/Elevator.jpg
width="120"></html>
601XL Corvair powered; Plans building.
Empennage done; working on wings and engine.
http://home.comcast.net/~kevinbonds
do not archive DO NOT ARCHIVE
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KevinBonds
Nashville, TN
Plans-building Zenith CH601XL w/Corvair Power
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naumuk(at)alltel.net
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| Posted: Sat Jul 08, 2006 5:01 am Post subject: Corvair cranks |
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Randy-
You're describing the guide bars, not the ejectors. They depend on
bushings for alignment and to cut down on wear.
You are right about the ejector pins and slides, though. TiN is used to
fill the surface imperfections of a part after grinding to cut down on
friction, thus surface wear. That's the concept behind a TiN drill bit. They
last longer not because they're tougher, but slipperier.
I have absolutely no idea how this applies to the Corvair cranks- you
just asked about TiN.
Bill
do not archive
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