Toasted my engine

"nrp" wrote in message
oups.com...

It could be undertorqued too. In that case there would be a lot of
fretting under the base flange of the cylinder, and probably on the
main bearing webs too.

Yes, but that wouldn't have sheared the bolt at the jug stud ring as the OP
said it did. You would get fretting at that location, but I don't see a
failure mode in shear.


If it hasn't been disassembled yet, you might check the other
throughstuds to see what torque is required to very slightly further
tighten them - giving you an indication of how close to the spec the
previous assembler was.

And how much torque it takes to loosen a couple of them.

Jim

"Yes, but that wouldn't have sheared the bolt at..."

I agree not sheared but it would have looked like that to the OP. I
would guess a tensile fatigue (probably initiated by bending) with the
crack starting on the side closest to the cyl centerline for cyl 3.
Assuming it is truly one of the bottom studs - they would not be
thru-studs but short ones instead. My guess is a partial loss of
preload of the #3 cyl assy initiated by the failure of the thru stud
between 2 & 3, then causing a progressive failure at the bottom of
three. There probably are also some cracks around the base of #2 also

I can't explain the crack at 4.

If the cyls are reused the flanges around the bottom should be subject
to very careful magnaflux inspection. Maybe on general principle they
should be junked.

Torque to loosen will be less than torque to tighten, and less
indicative. The engine history would be interesting. It certainly
would have failed in a few minutes rather than hours - and it would
have been a massive noisy failure too.

A Bonanza friend found one of those short studs laying in the cowl
while preflighting his airplane in the Bahamas. He put the family on
commercial airlines & flew home on minimum power - with a life jacket
on!

On 9/20/2005 12:44, nrp wrote:

[ snip ]


A Bonanza friend found one of those short studs laying in the cowl
while preflighting his airplane in the Bahamas. He put the family on
commercial airlines & flew home on minimum power - with a life jacket
on!


Yea, 'cause sharks like life jackets ;-)

--
Mark Hansen, PP-ASEL, Instrument Airplane
Sacramento, CA

"nrp" wrote in message
oups.com...
"Yes, but that wouldn't have sheared the bolt at..."

I agree not sheared but it would have looked like that to the OP. I
would guess a tensile fatigue (probably initiated by bending) with the
crack starting on the side closest to the cyl centerline for cyl 3.

Hm. Most people can detect the crystallization of fatigue as opposed to the
clean cut of a shear. Perhaps not. However, the OP clearly stated that it
was a throughbolt, not a stud.

I agree with the centerline analysis ... those pistons are slapping up and
down a hell of a lot harder than left and right (we hope).



Torque to loosen will be less than torque to tighten, and less
indicative.

Respectfully disagree. WIth torque values of these magnitudes, you will get
very little movement to find the point of actual torque by tightening.
However, just before the nut loosens you will generate very nearly the tight
torque. The problem is to have somebody reading the reverse torque very
carefully and noting the peak while you VERY SLOWLY bring the nut off.

It is, as they say, an interesting (and very expensive) problem in forensic
mechanics.


Jim