Author Topic: Cylinder head flatness (Read 8749 times)

jadecuir · « **on:** August 13, 2006, 01:49:28 PM »

I've searched and searched through this site and others but can't find the acceptable limits of warp for my M42 head. Mine is a little wavy, about .0025" (inch) out of flat near #2 cylinder, where the leak in the gasket occurred (overheat incident). Should I resurface?

nickmpower · « **Reply #1 on:** August 13, 2006, 02:04:11 PM »

theres probably a crack right there, between one of the water jackets and valve

jadecuir · « **Reply #2 on:** August 13, 2006, 03:30:51 PM »

It leaked thru the warp area just slightly. No visible cracks. I stoned the whole surface to highlight the highs and lows. The deepest warp is adjacent to #2 cylinder ( the one that collected coolant overnight) and is about .0025" deep.

nickmpower · « **Reply #3 on:** August 13, 2006, 04:10:11 PM »

have it pressure tested and resurfaced at a machine shop. Make sure to have it pressure tested

silverblades181 · « **Reply #4 on:** August 13, 2006, 04:56:51 PM »

the acceptable limit is usually around 0.003" but I don't know about the M42

jadecuir · « **Reply #5 on:** August 13, 2006, 05:31:30 PM »

It's funny how the manual says to check for warp, but doesn't say what the limit is for this engine. The most stringent requirement I've found is .03 mm, or .0018 inch. The least stringent is .10 mm, or about .0070 inch.
The car was running fine. Just replaced radiator for broken tank and housing cracks. But, on cold startup, engine would misfire for 20 seconds or so. I pulled the plugs and checked compression - OK. I pulled them again after overnight cooldown; ejected water from #2 cyl. Not much, but enough to know something wrong. After pulling head, the gasket is shiny on low side of #2 cyl.
Stoned entire surface with fine machinists stone; high spots adjacent headbolt holes, and lows between cylinders and on exhaust side of cylinders, between bolts. I think a new headgasket will compensate for warp, but I'd like to be sure. I'll check into cost of resurface and/or rebuilt head. I'd like to avoid messing with cams and lifters, though.

nickmpower · « **Reply #6 on:** August 13, 2006, 05:34:57 PM »

resurface is around 30 at least at my local shop, but you really shoud get it pressure tested too which will be around another 30 and will be good insurance

jadecuir · « **Reply #7 on:** August 13, 2006, 06:07:53 PM »

I live in Salinas, CA, and it's hard to find a good shop. The last one I used when out of business. I may have to look towards San Jose.

Febi Guibo · « **Reply #8 on:** August 13, 2006, 06:20:05 PM »

can't tell from your post if you saw this or not... it's .03mm

jadecuir · « **Reply #9 on:** August 13, 2006, 06:49:15 PM »

That's what I was looking for! Thanks, and where do I find the rest of this manual?

jadecuir · « **Reply #10 on:** August 13, 2006, 06:52:44 PM »

I found it, thanks.

jadecuir · « **Reply #11 on:** August 14, 2006, 08:30:35 PM »

I took the head to a local shop for the resurface and pressure test. They removed the cams to let the valves down. He called later today to say he would have to remove the valves also. Seems there is only .003 inch clearance between the present head surface and the edges of the valves. I'll have him measure the overall height to see if it's still standard (140.00mm).
Does this sound normal to you? Pretty close!

Febi Guibo · « **Reply #12 on:** August 14, 2006, 09:35:53 PM »

The machined limit for the height of the head is 139.55mm ....pass the micrometer.

dude8383 · « **Reply #13 on:** September 07, 2006, 02:10:14 PM »

Quote from: jadecuir

I took the head to a local shop for the resurface and pressure test. They removed the cams to let the valves down. He called later today to say he would have to remove the valves also. Seems there is only .003 inch clearance between the present head surface and the edges of the valves. I'll have him measure the overall height to see if it's still standard (140.00mm).
Does this sound normal to you? Pretty close!

how much did that cost you? to have the valves removed that is...

dave45056 · « **Reply #14 on:** November 13, 2006, 01:25:50 PM »

I once had to get a thicker HG for an M42 (Than the standard BMW thicher version) Cometic was very helpful in getting the specs etc for me.