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Old 02-24-2013, 05:16 PM   #1
matt_ali_walsh OP
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Valve Seats

Hi All,
I'm installing new valve seats in the '77 R100RS. I can't seem to find the spec for the valve protrusion anywhere. It may be called valve stem protrusion (past the guide). Can anyone shed any light??
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Old 02-24-2013, 06:43 PM   #2
bmwrench
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I don't think a spec exists for that. There is (an unpublished) spec for valve spring installed height, though: 36mm is the minimum. Anything more than 38mm makes valve clearance adjustment near impossible.
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Old 02-24-2013, 08:12 PM   #3
supershaft
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Quote:
Originally Posted by bmwrench View Post
I don't think a spec exists for that. There is (an unpublished) spec for valve spring installed height, though: 36mm is the minimum. Anything more than 38mm makes valve clearance adjustment near impossible.
The stack height spec is in BMW manuals and others. IMO, you want to leave the valves about as proud as you can and let the stack height fall were it may. The stack is usually under spec in my experience anyway. If it's a lot under spec, always check for coil binding. You really have to watch it with aftermarket valves. A lot of them have shorter than stock stems for some reason.
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Old 02-24-2013, 10:25 PM   #4
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Old 02-24-2013, 10:44 PM   #5
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Quote:
Originally Posted by bmwrench View Post
I don't think a spec exists for that. There is (an unpublished) spec for valve spring installed height, though: 36mm is the minimum. Anything more than 38mm makes valve clearance adjustment near impossible.
Written by someone that actually reconditions heads.

I find this is often overlooked by others (no, not you bmwrench ) when they do head reconditioning. The spec is available and published for the pre-70 machines.

There is a reason that valve spring height micrometers are made!

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Old 02-25-2013, 01:19 PM   #6
supershaft
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You guys ARE right in that the stack height isn't published but then again the spring test height is probably the same thing. At least it is in the /2 manuals. I highly suspect the same deal with the later models. 37.5mm A little thinking gets me to thinking that is the stack height spec but I could be wrong. Of course, this is written by someone who has reconditioned I am guessing around 200 sets of BMW airhead heads. I haven't done the machine work for a while now but it hasn't been THAT long ago.
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Old 02-25-2013, 05:19 PM   #7
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Any opinions about that spring test height in airhead manuals?
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