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Old 4th December 2017, 22:19
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Default Near disaster

The timing cover on the BMW M52 engine has three M6 torx-head bolts that go down through the cylinder head into the top edge of the timing chain cover. I was refitting the cover and following the tightening procedure in the Bentley workshop manual. It said to tighten the M7 bolts to 15Nm. Without checking I assumed that the bolts were M7 and set my torque wrench to 15Nm. As I started to tighten the bolts it was odd that the bolts kept turning without the wrench reaching it's clicking point. At first I thought it was just the new gasket compressing when suddenly one of the bolts gave way and went loose.

Timing chain cover bolts by Sabrebuilder, on Flickr
Timing chain cover bolts by Sabrebuilder, on Flickr

TBH I thought I'd snapped the bolt and was amazed that when I removed the bolt it came out complete albeit stretched by a few mm.
It turned out that the bolts are M6 and the correct tightening torque for M6 bolts is 9-10 Nm but I'm still surprised that these bolts would stretch to the point of fracture before only 15Nm.

Anyway, no harm done and I now have a new set of bolts from BMW.

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