How to determine how much a cylinder head has been milled

[jdaigle]

I wondering if anyone had the specs on where to measure and what the measurements are to determine how much a cylinder head S50/S52, has been milled. I just milled 0.010 off of mine, but would like to determine if any had been taken off prior, so I can select an appropriate head gasket thickness. Thanks, Jeff

[tjm3]

The only spec in the BMW docs is new head thickness - 140.0mm .

[jdaigle]

hmm, interesting, thanks! I'll have to poke around with the calipers and see what is close to 140mm... I'LL report back if I learn anything!

[jdaigle]

yup, just measured quick, this is the overall height of the head! great, thanks again

[bluptgm3]

Total height of head - I think the dimension is 140.000 mm. No machining allowed for S50/52, that said the difference can be made up with head gasket thickness.

I don’t recall seeing the same “no machining” note for M50/52. My take is that the S50/52 has higher lift that could be a problem if the piston to valve distance is reduced.

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[tjm3]

I saw a minimum thickness spec somewhere and I think it was in the AERA data. I'll check it when I get a chance. But there is room to shave the head a bit if there's some runout. Done it many times. My take is that anything that could boost the compression even a little bit could affect the emissions output, especially the NOx on these engines, so they don't recommend any trimming. If you think this is not a concern then remember we got the juvenile version of this engine, not the adult setup.