Valve Guide Clearance

[NC325iC]

So, I got a call from the machine shop yesterday where I took my block, head, crank, and pistons. I asked them to clean up the block and hone the cylinders, clean the crank and pistons, and measure some stuff for me. They did all of that except measure stuff for me which was a bit annoying. They also told me just to order the standard bearing sizes... anyway I'll deal with that later.

They also told me that my valve guides are worn out. So I did a bit of research and found two posts that both seem to indicate the same thing.

First, a post on m42club that describes the BMW manner of testing the guide clearance as setting the valve fully in the seat and rocking the valve side to side and measuring the play to be under 1.0mm.

Second, e30zone lists the stem-guide clearance as .020"

both of these posts corroborate each other.

I relayed this information to the machine shop and they said there's no way that's correct. Standard wisdom shows .001"-.004" stem to guide clearance.

Personally I am inclined to believe the bmw internet over a small town NC machine shop. At the same time new guides are gonna be less than $100 so im not too worried about getting new ones.

Can anyone out there produce the TIS info for valve guide clearance?

[NC325iC]

http://www.m42club.com/forum/index.php?topic=7770.0

https://www.e30zone.net/e30wiki/index.php/M42#Valves

[TobyB]

Stem clearances usually run in the 0.001- 0.002" range, new. As in, tight. maybe 0,020 mm. not 20 thousandths of an inch.

"Wiggle" is how you and I get a quick and dirty 'is it really shot' guess. A shop will run a ball feeler in there, measure it, and
run new guides in if it's more than 3 or 4 thousandths too big.

Usually not much expense if you're having the valves and seats done, and well worth it to keep wear of same under control.

That said, the M42's a lot easier on guides than the M20/M10 where the rocker's trying to shove the stem out the side of the head.

whut I seen and done,
t

[NC325iC]

I've got new guides on order for 7mm stems. Will see how they fit when they arrive.

[econti]

I had to mix and match bottom end bearing halves to get the desired clearances, so you may find yourself having to get a slight oversize set as well to get it spot on.