Broken Motor Mount Bolts Revisited

[High Velocity]

I know there have been other posts about the front motor mount bolts breaking, but has anyone figured out the actual cause of this ? For the first few years I owned my '06, I never experienced this bolt issue but would still replace the bolts with new grade 8 pieces any time the engine was out. In the fall of '09, I rebuilt my engine with the updated crank, new case, etc. and installed all new mounts and grade 8 bolts. Oct./10 I was doing steering linkage repairs and found a broken bolt - right front mount. Pulled engine and repaired. All new bolts again. Yesterday, I was rolling my sled over to get it unstuck and heard something rattling around. Checked it out this morning and the same right front mount bolt is broke again. Any thoughts on why this is occurring now after four seasons with no bolt issues ?

 

[millwall]

More than likely the rubber mount is broken inside, there are some posts from MH on this issue with pics. The motor is shifting/rotating too much and breaking the bolt, so maybe another mount is broken, leading to this excessive engine movement. Grade 8 bolts are fine. L9 grade are another stronger option.

 

[guidoxpress]

same thing happened to the wifes 06 700...busted the MAG front bolt last year, and mid season it busted the PTO side...

using compfusion mounts, greade 8 bolts...hopefully it stays this time...but ive literally done EVERTHING i can to prevent this...but still happened 2x? will see after this season again...

 

[High Velocity]

It's kinda weird that I never had issues until I replaced all mounts and bolts (gr 8) last season. Oh well, when I tear it out, I'll inspect all the mounts again as well as the bulkhead for any signs of cracking/flexing. I'll also likely order L9 bolts this time.

 

[AKFusion700]

Do you happen to know the specs for all the engine mount bolts?