M42 - Exhaust Valves Leaking

[Low Level E30]

Trying to help out a buddy w/ a 318is:

His car stalled and won't start. His mechanic told him that three cylinders have very low compression because the exhaust valves are leaking, and that the fix will need to be a $2,000 valve job.

I'm not an M42 expert at all --- anyone here have any experience with this?

How 'bout swapping on a replacement head and head gasket, from a used motor?

Thanks!

[FredK]

How low is low? I've seen an M42 with 90, 120, 90, 110 start and run smoothly.

[Low Level E30]

I don't know - this is just the info he gave me, verbatim from his mechanic.

Leaking exhaust valves would probably cause a more significant compression drop, wouldn't they, as the cylinders are improperly sealed? I guess it would depend on the severity of each leak.

Does $2,000 for the valve job sound correct... ? I'm a li'l skeptical.

If 2k is correct, it's obviously not worth it - so would a spare head and new HG fix it?

[gazellebeigem3]

I don't know - this is just the info he gave me, verbatim from his mechanic.

Leaking exhaust valves would probably cause a more significant compression drop, wouldn't they, as the cylinders are improperly sealed? I guess it would depend on the severity of each leak.

Does $2,000 for the valve job sound correct... ? I'm a li'l skeptical.

If 2k is correct, it's obviously not worth it - so would a spare head and new HG fix it?

If the valves are the only thing causing the leak (or at least the majority that is causing the no start) then yes a spare head, providing its ok, will fix it.

As for the 2k, its probably including the labor to r&r the head as well as the cost of parts/labor for the head job. It sounds a little on the high side but not by too much.

If it was my car, i would pull the head and send it to a machine shop to be gone through and refreshed. It would be a kick in the pants to go through the trouble of swapping heads for the 'new' one to take a shit a little later.

just my .02

[FredK]

Yeah, I agree with gazellebeigem3. The M42 is not an expensive head to get done, it's got 50% fewer valve seats than a six cylinder. :)

How many miles are on the engine? If it is something like 220k, I would suggest swapping in a lower mileage engine from an E36. The timing system on an M42 doesn't age that well, especially when it's driven hard. Also by then, the rings aren't sealing as well as they used to.

[Low Level E30]

157k on the car + motor, and carefully maintained, apparently.

Thanks for the help - I'll pass on the info!

Cheers,

[Low Level E30]

Ok, more questions:

- How common is this in M42's with this mileage?
- What else should be replaced while the head and HG are being replaced?
- Is this a good time to replace piston rings or rod bearings?

Thanks,

[gazellebeigem3]

I have limited experience with the m42 as far as higher mileage ones go, so i cant really offer any insight. You best bet would be to check out m42 club. http://www.m42club.com/forums/

[Hick]

m42s have been known to have cracked heads as well; cracked into coolant passages. Not sure exactly where they are more common.

As for the miles, im at 149k and running well. The motor should technically have 5k more or so because the Odometer stopped working.

[gazellebeigem3]

m42s have been known to have cracked heads as well; cracked into coolant passages. Not sure exactly where they are more common.

As for the miles, im at 149k and running well. The motor should technically have 5k more or so because the Odometer stopped working.

your head has been rebuilt though

[strad]

My motor has 194k on it, and has only been apart once to replace the profile gasket (at 34kmiles) according to the complete service history that I have. I have no problems other than a little bit of blue smoke at cold startup if I do the no-no rev.

How about thoroughly inspecting the timing case and all its gaskets, guide rails, sprockets and chains while you have the head off? That's what I would do.