Wack ass M42 noise...

[Erick]

And no, it's not just the fact it's a 4 banger :p

My question: Are there any plastic components in the motor/chain?

I have a terrible noise coming from my motor. It sounds plastic on plastic.... as if the clutch fan was continuously slapping on the shroud (not the case).

Symptoms:

It happens at idle and at other random times, mainly on the lower RPMs.

I put my ear to the engine bay and it sadly sounds like it's coming straight from the motor. But I've heard valve tick (with enough M20s) before and this sounds nothing like it.

It's not fan related, because when you shut the motor off, the noise quits before the fan comes to a stop.

At idle, with the noise happening, if I flick on the A/C, the noise will go away, but it will come back once you rev it.... dissapearing again when the car goes back to idle. Turn the A/C off and the noise comes back at idle.

I'll see if I can grab a video of it.

Thoughts, suggestions? The math just doesnt add up to me, and I'm thinking it's something inside the motor. Unfortunately I have no tools right now to take the valve cover apart as my tools are in storage with the other e30.

- Erick

[tjts1]

Timing chain rails are shot. Search M42club for the info.

[Erick]

That search function sucks there. Either "timing chain rail" is the most used word with these M42s, or there are just no write ups.... other than people just posting what to do.

Any link to a write up?

Thanks
Erick
PS: Where's this whole DOHC reliability crap? My M20 has been 10x more bulletproof than this M42. AND it was boosted. :p

[mooseheadm5]

Replace the timing chain tensioner. It screws into the side of the lower timing cover near the top. It may or may not resolve the issue, but it might be OK if the noise just started. If it has been like this and getting worse, you need to replace the tensioner and rails immediately or else you will need to pull the head off and replace valves when the chain breaks or skips a few teeth.

[Liam]

Yes, probably a worn chain tensioner.

Pop the rocker box cover off and look at the chain (you really want to do this anyway to replace the tensioner).

Look at the rails and the upper guide (if they're not okay take 2 aspirin and PM me).

When you replace the tensioner you need to release it and pump up the oil pressure before you run the engine.

It doesn't happen every time but if you replace the tensioner without doing this it can let the chain skip (and that's no good).

[rThor432]

Replace the timing chain tensioner. It screws into the side of the lower timing cover near the top. It may or may not resolve the issue, but it might be OK if the noise just started. If it has been like this and getting worse, you need to replace the tensioner and rails immediately or else you will need to pull the head off and replace valves when the chain breaks or skips a few teeth.

To add to this post, use the M44 tensioner-- it is an updated design. My M42 with 140k had the rattling noise going on and I was afraid I would have to tear down my dd to do the chain rails. I rolled a new tensioner into it and it fixed the entire problem. No more noise.

Oh, and the whole DOHC reliability thing is a myth. My 250k eta didnt burn a drop of oil and couldnt be killed. My 70k S52 actually uses a small bit of oil and it seems bizarre to me because I'm not used to that, even though it is totally normal.

[e304me]

it could be the ac clutch, try taking the belt off

[FredK]

Personally I feel the M42 is more unreliable than the M5x engines. The timing case, the oil pump design, etc. It is inherently more rattly, and the oil pan is such that there are a few bolts on the inside that can fall into the mix, get sucked into the suction tube, starve the engine/pump of oil.

[gearheadE30]

I rebuilt the entire timing case awhile back, so if you have any questions about that, PM me. Sounds like classic tensioner wear case to me. If its been that way for long, it may have also worn the cam gear teeth to points and/or worn the guides badly.

I personally have had zero reliability issues with my M42; no leaks, no drips, doesn't burn oil, runs really smooth and quiet, and doesn't rattle at all. There are some parts that have a questionable design, but they're all pretty easy to fix or check.

[Liam]

Personally I feel the M42 is more unreliable than the M5x engines. The timing case, the oil pump design, etc. It is inherently more rattly, and the oil pan is such that there are a few bolts on the inside that can fall into the mix, get sucked into the suction tube, starve the engine/pump of oil.

Every power-plant has it's issues and the m42 has it's own. like the one you mentioned with the upper pan bolts (there was a TSB on that and there is a fix).

But I can tell you from experience that a well cared for m42 can make 300k plus miles (the last one I was forced to get rid of had about 365k and was still going good the last I heard) I have several very high mileage ones that regularly come through the shop.

Same thing goes for the M50, TU, 52... These are very durable power-plants. However, I have see few of these (even well maintained regular customers cars) go beyond the high 200Ks. I think this could be due to pulling much heavier cars (and possibly a little less love involved from the driver?).

[tjts1]

That search function sucks there. Either "timing chain rail" is the most used word with these M42s, or there are just no write ups.... other than people just posting what to do.

Try harder.