Question about decking the block and timing cover

[tzei]

Non machined block height is 217.0 mm (crank journal cl to deck) if you want to measure how much has been skimmed off.

[kbmb02]

2 hours ago, tzei said:

Non machined block height is 217.0 mm (crank journal cl to deck) if you want to measure how much has been skimmed off.

 

^ Good info.

 

Did you find a spec on that in the BMW blue book, etc?

 

As another data point: I find M10 blocks are a little taller than that (above), on engines which don’t appear to have been decked after the factory:  8.556” | 217.3 mm   -KB

[tzei]

27 minutes ago, kbmb02 said:

Did you find a spec on that in the BMW blue book, etc?

Actually no, it’s what i have measured. Wonder what was Factory tolerances for this?

[Hans]

I tried to have an upper cover milled after the fact, and they couldn't get it to exactly 90 deg. Leaked. 

Also, why are they taking something off the bottom?

[bergie33]

37 minutes ago, Hans said:

I tried to have an upper cover milled after the fact, and they couldn't get it to exactly 90 deg. Leaked. 

Also, why are they taking something off the bottom?

 Well, I hope they can work magic, otherwise they may just have to skim the block a little more with the cover attached.  The bottom was off a couple thou. Maybe it has something to do with the fact the cover was not from that block originally.

[Hans]

13 hours ago, bergie33 said:

 Well, I hope they can work magic, otherwise they may just have to skim the block a little more with the cover attached.  The bottom was off a couple thou. Maybe it has something to do with the fact the cover was not from that block originally.

Don't forget, it has to  line up in two dimensions. I don't see how they can do it off teh black, but I could be wrong.

[bergie33]

On 1/14/2022 at 4:11 PM, kbmb02 said:

 

^ Good info.

 

Did you find a spec on that in the BMW blue book, etc?

 

As another data point: I find M10 blocks are a little taller than that (above), on engines which don’t appear to have been decked after the factory:  8.556” | 217.3 mm   -KB

 

I got the block and lower timing cover back from the 2nd machine shop, they did a great job.  They were able to keep the cover bolted to the front of the block and shave them down together.  Now everything is nice and level.

 

Now to kbmb02's message above, the shop measured the block out at 8.557" (217.35mm), which seems right on spec, even after a little was shaved off (weird).  With the head measuring 128.7mm, it sounds like I can go with a stock thickness head gasket, correct?  Or would it be better to play it safe and use the 1.8mm head gasket (since both surfaces had material removed and my pistons are now 9.5:1 instead of the stock 9.0:1)?  I already bought the 1.8mm, but can return it and get the 1.5mm if that would be better.

Edited January 25, 2022 by bergie33

[mike472]

Since your block has been decked and your head has been cut I would take the thicker head gasket.  If you take too much off either your head or block surface your cam timing will change and will need to be compensated for with an adjustable cam sprocket and a degree wheel to check it.  Use Elring-Dirko gasket sealant for all gasket surfaces.  It's what BMW uses.  Here's a link to Ireland's site for sealant:

 

Elring Dirko Silicone Sealant – Ireland Engineering | Racing & Performance Parts for BMW & MINI

WWW.IEMOTORSPORT.COM

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Each

 

[bergie33]

That was my original thought process, such is why I originally bought the 1.8mm gasket. I'll go ahead and use that then.

[kbmb02]

On 1/24/2022 at 5:23 PM, mike472 said:

If you take too much off either your head or block surface your cam timing will change and will need to be compensated for with an adjustable cam sprocket and a degree wheel to check it.

 

In reality (as I'm sure @mike472 knows), any amount of surfacing changes the camshaft timing. In small increments - and with stock components - the resultant change in cam timing won't typically make a notable difference in performance, or reduce piston to valve clearance enough to be a problem. BMW's tolerance appears to be up to 0.3 mm (0.012” +/-), which is the additional thickness of the 1.8 mm head gasket.

 

When more material is removed and/or non-stock components are used (camshaft, pistons, etc), the need for an adjustable cam timing gear and checking becomes criticially important. -KB

 

 

Edited August 13, 2023 by kbmb02
typo + clarification