Brokoen bolt on engine mount

[undertow]

These are a bit of a lottery. I've had to do it before (pain in the rear) but my current manual XR8 has 220,000 on the original bolts.

As said above it's likely caused by poorly formed mount plates... a grade 5 7/16 bolt has a yield strength of ~40 kilonewton, endurance limit would be ~20kN, so the two of them *should* handle ~40kN loads indefinitely without fatigue failure.

A wheezer will put about 1300Nm torque into the mounts in first gear (3:1 gear ratio), the bolts are about 20cm from the crank centreline so that's about 6.5kN into the bolts. So a safety factor of about 6x below the endurance limit which should be plenty even allowing for shock loading from clutch dumps, axle tramp etc. But if the mounts are not true (I'd bet some came from the factory like that) and load the bolts unevenly all bets are off.