Why do my engine bolts keep breaking?

Hi Syncronauts.
My 2.1 MV is constantly breaking the rear engine bolts (which there are 2 of)…four times in the last 5 months.
These are behind the muffler and go through the aluminium cradle bracket (whick looks fine)…they are separate from the moustache bar.
They shear off, and then the 10mm or or so needs to be removed from the engine case (with Ezyout)…very labour intensive.
The next option is to replace the 4 rubber mounts (which don’t look too bad) and the cradle.
I’ll be showing these broken 8.8 high tensile bolts to the supplier.
The moustache bar looks fine.
And on start-up the engine doesn’t vibrate too much.
Any clues anyone?

Which bolts on this diagram are breaking Gerry?

Sometimes its difficult to see if the engine mounts have failed as the weight of the engine makes them look fine.

Might be worth while removing them and checking them.

Hi Scott.
Thanks for picture.
It’s the one marked as 7.
There are 2 of them…
The one on the LHS (not shown) is the one that usually breaks…although 2 have sheared now…the left one, then a few hundred kms later the right one.
4 new engine mounts are on the way from Tooleys.
Febi and Meyle.

I suspect the engine mounts hold the key to your problem.

Otherwise go back to the stock VW engine from that thunderous W12 turbo diesel you have in there!

Well…we’ll see what happens next.
Where do you get a “thunderous W12 turbo diesel” from?

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The early Touregs had these and they had around 600Nm of torque which is just ridiculous…how would a gearbox cope with that - let alone the poor engine mounts?


Anyway let us know how your replacement goes - as we agreed in our phone conversation - the lost likely cause of the breakage is the bolts coming loose and then allowing everything to move around followed by a breakage.

I’m interested to see the fixes and how well they work.



Hi Gerald, wondering if your latest fix has been successful on these bolts? It does seem a mystery as not a common part to fail.

Hi Scott and Richard.
My local mechanic put in 12.8 bolts, (with Allen key heads) a little Loktite, and torqued up to 55ft lbs a little while ago.
So far, so good.

Hi Gerry,
Curious about the 12.8 bolts installed by your mechanic because the ETKA schematic lists 2 x M10 x 85mm hex head bolts.

So for the replacement bolts, has he had to drill out and re-tap the caste alloy bracket?

Hi Ken…the 12.8 refers to the strength, not the size.
Originals are 8.8.
So, we put in 85mm x 10mm x 12.8.

Where did you find the specification of 8.8 for the originals?

Are the replacements zinc plated? (silver of gold colour)?

8.8 is stamped on the heads.
The new 12.8’s are black…and is also stamped on the heads

Thanks Gerry … never had reason to think about different grades of high tensile steel bolts when at the local specialist bolt and nut supplier.

Cheers. Ken. :smiley:

Sounds good. I just looked at mine, I thought they were 10.9, but no, they are 8.8 as you noted.
With grade 12.9 bolts, the torque is important to prevent fatigue cracks in the future.

Lets hope what you have will fix the issue!