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