N52 valve cover gasket replacement

bigwinn · Post by **bigwinn** » Sun Mar 17, 2024 9:50 am

Mr Tidy wrote: ↑Sat Mar 16, 2024 11:42 pm The previous owner of my 330i with the N52 had a new cam-cover gasket fitted just before I bought it by a local garage, but told me he had insisted they used new bolts.

The invoice includes the comment "Found front O/S corner of rocker cover had 2 bolts snapped off and been left in holes" so they had to drill them out!

Shame he didn't get the oil filter housing gasket replaced though.

Ooof

Blimey

enuff_zed · Post by **enuff_zed** » Sun Mar 17, 2024 11:21 am

In the past few weeks I’ve done an E89 and an E85. Both black top. Both had magnetic bolts so not ally and I reused them. Although captive, some of the captive collars come out with the bolts. Note which are which as the corner ones have a slightly bigger collar and won’t fit anywhere else.

Mr Tidy · Post by **Mr Tidy** » Sun Mar 17, 2024 7:41 pm

Maybe it's only the Silver tops then?

Z4Mariner · Post by **Z4Mariner** » Tue Mar 19, 2024 1:19 pm

Correct - Al bolts for Silver Top, Steel for Black Top. My 128i convertible had the Black Top and my E86 has the Silver Top.

pvr · Post by **pvr** » Tue Mar 19, 2024 1:51 pm

Wonder what the Pro is of using Alu bolts as non re-usable seems a bit of a pain

enuff_zed · Post by **enuff_zed** » Tue Mar 19, 2024 2:30 pm

pvr wrote: ↑Tue Mar 19, 2024 1:51 pm Wonder what the Pro is of using Alu bolts as non re-usable seems a bit of a pain

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

j3nks79 · Post by **j3nks79** » Tue Mar 19, 2024 4:07 pm

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

enuff_zed · Post by **enuff_zed** » Wed Mar 20, 2024 12:48 pm

j3nks79 wrote: ↑Tue Mar 19, 2024 4:07 pm 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

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?

Z4Mariner · Post by **Z4Mariner** » Wed Mar 20, 2024 1:10 pm

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.

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