M20 Machining and those divots

[Earendil]

I have just recently read, when looking for M20 head specs, that there are supposed to be divots on the head that look like these ones here:

http://imageshack.us/a/img339/719/head1im.jpg

However, in looking for those specs, I've found a lot of people saying they've never seen those divots. I've looked at pictures of my head and the only head I've ever worked on and also don't see those divots. So the question is, do some heads not have them? Or are there a lot of M20 heads shaved well out of spec without the owner knowing it and the car running fine?

If those divots are now gone, how does one tell how far passed the divots the head is so that a proper over sized gasket can be chosen?

[digger]

Bentley has specs for head thickness IIRC

[AwakenNoMore]

Dunno, my head still had them after a skim. Maybe it depends on when or who manufactured the head? I know there are a few different ones.

[ForcedFirebird]

Bentley has specs for head thickness IIRC

4.909" minimum height.

[Earendil]

Right after I posted this the machine shop called and said the head was done, so I went down there and picked it up. They said they had to take 10/1000 inch off. Turns out I must have been looking at pictures of a different head than my own, because even after taking off 10/1000 inch I still have all 4 divots showing!

For the record, mine is an 885 head. My Dad's ix has an aftermarket AMC head that the machine shop said was better than spec in straightness. I don't know if it's ever been machined, but it didn't have a sign of divots, nor does it run poorly. *shrug*

[digger]

if you machine a smidge off below the dimples the sky wont fall down anwyay

[Ether-D]

if you machine a smidge off below the dimples the sky wont fall down anwyay

I can also personally attest to this.

[Earendil]

if you machine a smidge off below the dimples the sky wont fall down anwyay

The problem is that once you're a smidge below, you don't know if you're a little smidge or a big smidge ;)

If, in the case of my Dad's head that doesn't have these markings on it (any more?), and the machinist wanted to take off 1000/2, how would we know if that was acceptable or not? I guess we could get him to measure the entire thing top to bottom? That assumes that the aftermarket heads had the same top-to-bottom spec tolerances that the BMW heads had.

[jlevie]

The Bentley spec is correct for a BMW head (which will have the dimples). But you can't say anything about an aftermarket head w/respect to the dimples or the overall height.

[ForcedFirebird]

The problem is that once you're a smidge below, you don't know if you're a little smidge or a big smidge ;)

With an OEM head, you most certainly know how far below. A stock unshaven head measures 4.925". Measure the head and subtract from 4.925" and you have how much was taken off.

[Ether-D]

You can also clay the valve clearance. That's what I did. It was actually fun.