Toasted my engine

There aren't a lot of possibilities, are there?

1. The case crack set up a vibration or torque that overstressed the
bolt -- and since it happened on startup when things are running less than
smooth in a Lyc, I'd bet on this one.

2. The bolt was WWAAAYYY overtorqued on installation. You'll never know
about this one. However, a through bolt shearing and a case crack by
another through bolt leads me to check the calibration on somebody's torque
wrench.

3. Something else in the engine was vibrating ... not likely as the whole
AIRplane would have been vibrating to shear a through bolt.

4. Defective bolt ... not likely as throughbolts get magnafluxed or x-rayed
at overhaul.

5. (Add yours here)


Oh, and BTW, mechanics cannot ground airplanes. IAs cannot ground
airplanes. The FAA (unless they pull the airworthiness cert.) cannot ground
airplanes. I know it is a common phrase, but the mechanic simply suggested
that it would be less than wise to fly the airplane in its current
condition.

Jim



"Jim Burns" wrote in message
...

I'd love to know what caused the through bolt to shear or snap.
Thanks for posting.
Jim

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.

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.

Another possibility is the hardness of the thru studs I don't know
what the spec is (probably not published ) but maybe Rockwell C = 48 to
52 or so?

That engine wouldn't have gone much further at all. You were lucky.

"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

Oh, and BTW, mechanics cannot ground airplanes
************************************************** *****
Yup, true fact...

Though one local recently got into a ****ing match with his API over
some annual inspection issues on a well worn TriPacer (couple of 3
year olds in adult bodies)-
including the CAR 23 original equipment single mag switch that has only
two positions - off and on -
and the fabric passing the punch test though at the lowest allowable
reading, and the mechanic refused to sign it off..

The owner (an AP but not an I) demanded the mechanic turn the plane
back to him now, or else... The mechanic did, but he put an entry in
the log book that the airplane was unairworthy and called the FSDO and
faxed them a copy of the log entry... It took a ferry permit to get it
off the field...
So, the plane was shopped around to several API mechanics before he
found one that would touch it... 6 months later and it is still not
flying... The story I hear is that the FSDO inspector is demanding
documentation that they are having problems coming up with...

While an mechanic cannot "ground" an airplane he can do a fair
imitation if he is determined...

denny

If the airplane was going through an annual inspection, the IA should
have generated a list of discrepancies of what didn't pass and given
that to the owner. At that point the annual was complete.

An ordinary A&P could then bring the aircraft back to airworthinness
condition without the need for the IA.

I don't believe that there is anywhere where the FSDO could have
demanded anything except to do a ramp inspection after the aircraft had
been flying.


Denny wrote:
Oh, and BTW, mechanics cannot ground airplanes
************************************************** *****
Yup, true fact...

Though one local recently got into a ****ing match with his API over
some annual inspection issues on a well worn TriPacer (couple of 3
year olds in adult bodies)-
including the CAR 23 original equipment single mag switch that has only
two positions - off and on -
and the fabric passing the punch test though at the lowest allowable
reading, and the mechanic refused to sign it off..

The owner (an AP but not an I) demanded the mechanic turn the plane
back to him now, or else... The mechanic did, but he put an entry in
the log book that the airplane was unairworthy and called the FSDO and
faxed them a copy of the log entry... It took a ferry permit to get it
off the field...
So, the plane was shopped around to several API mechanics before he
found one that would touch it... 6 months later and it is still not
flying... The story I hear is that the FSDO inspector is demanding
documentation that they are having problems coming up with...

While an mechanic cannot "ground" an airplane he can do a fair
imitation if he is determined...

denny

wrote in message
...

If the airplane was going through an annual inspection, the IA should have
generated a list of discrepancies of what didn't pass and given that to
the owner. At that point the annual was complete.

I'm not sure what you are saying. That the airplane has a current valid
annual at this point? That isn't so. THe logbook should have contained
words to the effect that the aircraft was inspected on (date) and a list of
unairworthy items given to the owner or operator.

If the airplane is "ratty" but the mag switch(es) had been installed in
accordance with the type certificate in effect as of date of manufacture and
there were no subsequent ADs to change it, then the IA cannot on his own
hook declare them unairworthy.

Similarly, if the fabric punched "at the bottom of the airworthy scale" then
the fabric is airworthy. THe IA does not get to set a higher standard than
the FAA requires.



An ordinary A&P could then bring the aircraft back to airworthinness
condition without the need for the IA.

That's true, but the aircraft still does not have a current annual
inspection.



I don't believe that there is anywhere where the FSDO could have demanded
anything except to do a ramp inspection after the aircraft had been
flying.

They can demand green cheese. What they get or are entitled to get are two
separate matters.

Jim

RST Engineering wrote:
wrote in message
...


If the airplane was going through an annual inspection, the IA should have
generated a list of discrepancies of what didn't pass and given that to
the owner. At that point the annual was complete.


I'm not sure what you are saying. That the airplane has a current valid
annual at this point? That isn't so. THe logbook should have contained
words to the effect that the aircraft was inspected on (date) and a list of
unairworthy items given to the owner or operator.

I was saying the annual inspection was complete and current at that
point and if there were any unairworthy items, they need to be attended
to. The IA had completed his duties and is no longer involved. Once he
signs off the annual inspection, whether airworthy or not, the
inspection is complete and current.


If the airplane is "ratty" but the mag switch(es) had been installed in
accordance with the type certificate in effect as of date of manufacture and
there were no subsequent ADs to change it, then the IA cannot on his own
hook declare them unairworthy.

Similarly, if the fabric punched "at the bottom of the airworthy scale" then
the fabric is airworthy. THe IA does not get to set a higher standard than
the FAA requires.



An ordinary A&P could then bring the aircraft back to airworthinness
condition without the need for the IA.


That's true, but the aircraft still does not have a current annual
inspection.

The inspection is current and complete, but not airworthy. That
inspection will be current for the next year and if it was not airworthy
it can be brought into airworthiness and flown during that time period.
The A&P has 0% authority with the inspection process.



I don't believe that there is anywhere where the FSDO could have demanded
anything except to do a ramp inspection after the aircraft had been
flying.


They can demand green cheese. What they get or are entitled to get are two
separate matters.

Jim