N52 valve cover gasket replacement

pvr said:
Wonder what the Pro is of using Alu bolts as non re-usable seems a bit of a pain
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Because if you use steel bolts into ally head there is a chance of dissimilar metal corrosion occurring. I have no idea what the difference is with the blacktop cylinder head though? Perhaps it has steel threaded inserts? But nothing obvious that I could see
 
IIRC they are stretch bolts. So once used they shouldn’t be re used.
It’s so the can have the correct torque and stop leaks
 
j3nks79 said:
IIRC they are stretch bolts. So once used they shouldn’t be re used.
It’s so the can have the correct torque and stop leaks
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You are probably right but given the tiny torque needed I don’t see how they would stretch? Doing them up that tight would deform the cover and make it more likely to leak I would have thought?
 
Pretty sure the Al bolts for the magnesium valve cover (VC) are there to protect the valve cover from dissimilar metal corrosion. The Black Top VC can use steel, since the VC is plastic, and the cylinder head is Al-only (not mixed Al/Mg like the N52 block).

The install instructions suggest to me that the Al bolts are installed with both stretch and gasket compression in mind, with a 30 minute wait period between initial torque and the extra 90 degrees. Even if not intended to stretch, the aluminum screws are prone work-harden and break if they are reused.

My background in corrosion chemistry probably leads me to over-think something like this. :wink:
 
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