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rsrandazzo(at)precisionma
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 Posted: Tue Aug 14, 2007 9:59 pm Post subject: Through Stud Sheer Pictures... |
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Commanders!
Here are a few (not so good) images of the sheered through stud.
It is interesting to note that the stud appears to have been damaged/bent at
some point. Possibly during installation? We found what appear to be
impact marks from a hammer or ram on one end. Go figure.
The internals of the engine appear fine- looks like a brand new engine on
the inside. No metal found in the oil, and the cylinder and pushrods are
fine.
We are trying to get some guidance on what should happen with this engine.
The hope is that the stud can be replaced- and we'll be good-to-go.
I'll keep you all posted.
Robert S. Randazzo
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floydgm(at)hotmail.com
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| Posted: Tue Aug 14, 2007 10:33 pm Post subject: Through Stud Sheer Pictures... |
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Robert,
With the expert input you are getting from Moe at Ross Pistons and Myron
Ashley you are receiving. You have more than enough input to figure this
out.
What I have seen before was the bearing shell coming loose in the crankcase
where it is clamped between the the cylinder through studs. The way to check
for that is to use a long probe on the bearing shell and see if there is
obvious movement between the case and the bearing.
Also examine the crankcase where the stud came out for cracks per David
Owens. They don't call them Crackinentals for nothing.
Mike
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mashley2(at)kc.rr.com
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| Posted: Wed Aug 15, 2007 7:59 pm Post subject: Through Stud Sheer Pictures... |
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Hello Robert,
It is hard to tell from the pictures but it appears that the failure is due
to fatigue and not excess load. Fatigue, in this application, typically can
be caused in two ways. One, the part has been in service to long (to many
cycles, this is hard to do with steel parts) or the part was not properly
torqued and vibration caused the cycle loading to become exponential,
therefore causing fatigue cycle failure. I simplified this explanation to
keep from putting you to sleep.
It makes you wonder if the torque was correct at first, but after operating
the engine, the mating parts of the engine "seated" against each other
thereby causing the stud or studs to become loose.
You might think about re-torqueing the new studs after ground run. This
would ensure that everything has had a chance to go through a thermal and
vibration cycle.
I hope this helps,
Myron Ashley
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rsrandazzo(at)precisionma
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| Posted: Wed Aug 15, 2007 9:18 pm Post subject: Through Stud Sheer Pictures... |
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Myron, Moe, et al-
Thanks for your input. We had the piece examined by a metallurgist and his
assessment was the same. He felt the part was likely damaged during a
previous removal- and was subsequently forced into this engine build. End
result being that the part failed...
We were able secure input from TCM today- (good contacts are worth their
weight in gold!) and their technical assessment was to replace the stud, and
the opposing cylinders/pistons/pushrods at that location. Once those are
installed- they provided a test to ensure that the bearing is within
limits....
This engine has <400hrs, so this will be a relatively low cost repair given
my initial expectations. Of course- it's another two weeks or so before we
can re-commence flight testing.
Thanks for your input, gents- it is always good to have corroborating
information.
Robert S. Randazzo
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