Bad bad noise

[Musij]

So driving home (40 miles) after doing my steering rack change, a nasty clanking noise appeared out of nowhere. It increased with RPMs. Trying to find it, I concluded it was coming from within the engine. Took out the oil and I found a lot of metal ( see pic).

After doing some research and getting advice from a mechanic I found that it was probably my chain, and it might be the tensioner. So I took the old tensioner out, stuck 2 small washers between it and the holding bolt, and the sound changed. Great. Ordered a new tensioner. Yesterday did a fresh oil change and put in the new tensioner. Now here's where I think I might have made a mistake. I read that it didn't matter whether to put the tensioner in compressed or decompressed. So I thought cool, compressed is easier.

FYI: the chain was done about 3 years ago. I bought the car 3 months ago and it ran incredibly till this happened. No clicking noise, nothing. The tensioner that came out was a modern m44 tensioner, the upgraded one. So I'm not sure how either of those could have gone bad so soon. None the less.

When I went to start the car, the worse noise I've ever heard from an engine started. The car doesn't start and the noise is loud. Check out the video to see what I'm talking about.

At this point I'm going to take the valve cover off to check out how the chain looks from up top, but does anyone know from the noise itself what it could be? You can feel something just being tossed around in the engine even on the steering wheel. I'm afraid it might be an engine killing problem.

https://youtu.be/oNPNrhNoICs

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[bmwman91]

It could be one of a few things. The tensioner is one, although unlikely. Also, putting it in uncompressed is really inadvisable since popping it loose requires that the chain slap around on the tensioner rail hard enough to free the piston. Always decompress it (wrap it in a rag when you do this so it does not fly apart) and then install it, even though it is more difficult. The exception is if you have the timing cover off. Then you can manually push the rail into it to expand it once it is in. It is possible that the chain jumped some number of teeth on either the cam sprockets or at the bottom (likely destroying the lower guide). If too many teeth got skipped, then the valves (and maybe bottom end) are finished. That is sort of what it sounds like in the video.

Next on the list is the top bolt in the large driver's side guide rail. Frequently, it will strip out, particularly if you rebuilt the timing case and upgraded to the newer plastic guide. It turns out that the newer guide requires a 45mm long M6 bolt up top, and the old guide's bolt was only 40mm long. When the top bolt strips out, it rubs on the timing case, makes aluminum shavings, and causes some bad noises. In your video though, I am fairly sure that the bad noise is not this.

The next thing I can think of, and this one got me back in 2012, is probably the worst of all. The deflector sprocket can snap off of the timing case entirely, and it gets jammed against the timing case and cover, grinding away on it. This causes a lot of slop in the chain, enough to have valves kiss pistons. When the noise first showed up (before replacing the tensioner piston), did the noise sound like the clatter of a diesel? If that was the initial failure, then putting in the uncompressed piston was likely the death blow since the chain become so loose that many many teeth got jumped, and the valves are completely toast. The M42 is actually very tolerant of valves hitting pistons, as long as you are only off by a couple of teeth, since the hydraulic lash adjusters can absorb this at low RPM. Once you are off by too many teeth though, things hit limits and valves bend, if not worse. To be honest, that is sort of what it sounds like is going on in your video, especially given the amount of shaved aluminum in the oil. Sorry to be a debbie-downer. Fingers are crossed that I am massively wrong.

In that case that the engine is basically toast. Used M42's are fairly cheap and easy to swap. Also, for less than $2000 you could probably have a nice OEM rebuild of the head and bottom end done, which would allow you to address this engine's biggest design flaws.
1) Upgrade to the 1994-1995 M42 timing case which uses a plastic guide instead of that awful deflector sprocket (direct bolt-in as long as you get all of the updated gaskets that go with it, check RealOEM)
2) Install a full 360 degree thrust bearing on the crank since the stock half-shell is weak BS (incidentally, NEVER start the car with the clutch pedal pressed in).
3) Make sure that the oil pressure regulator assembly in the bottom of the timing case is the newest design which is not prone to seizure like the original one.

Good luck, let us know what you find.

[e30sh]

f that was the initial failure, then putting in the uncompressed piston was likely the death blow since the chain become so loose that many many teeth got jumped, and the valves are completely toast

Can you expand on this?

I thought the purpose of putting the tensioner in a vice and compressing it was to aid in the ease of installation. If not compressed when installing, the tensioner starts pushing on the guide rail making it difficult but not impossible to get the the threads started in the head.

[Musij]

It could be one of a few things. The tensioner is one, although unlikely. Also, putting it in uncompressed is really inadvisable since popping it loose requires that the chain slap around on the tensioner rail hard enough to free the piston. Always decompress it (wrap it in a rag when you do this so it does not fly apart) and then install it, even though it is more difficult. The exception is if you have the timing cover off. Then you can manually push the rail into it to expand it once it is in. It is possible that the chain jumped some number of teeth on either the cam sprockets or at the bottom (likely destroying the lower guide). If too many teeth got skipped, then the valves (and maybe bottom end) are finished. That is sort of what it sounds like in the video.

Next on the list is the top bolt in the large driver's side guide rail. Frequently, it will strip out, particularly if you rebuilt the timing case and upgraded to the newer plastic guide. It turns out that the newer guide requires a 45mm long M6 bolt up top, and the old guide's bolt was only 40mm long. When the top bolt strips out, it rubs on the timing case, makes aluminum shavings, and causes some bad noises. In your video though, I am fairly sure that the bad noise is not this.

The next thing I can think of, and this one got me back in 2012, is probably the worst of all. The deflector sprocket can snap off of the timing case entirely, and it gets jammed against the timing case and cover, grinding away on it. This causes a lot of slop in the chain, enough to have valves kiss pistons. When the noise first showed up (before replacing the tensioner piston), did the noise sound like the clatter of a diesel? If that was the initial failure, then putting in the uncompressed piston was likely the death blow since the chain become so loose that many many teeth got jumped, and the valves are completely toast. The M42 is actually very tolerant of valves hitting pistons, as long as you are only off by a couple of teeth, since the hydraulic lash adjusters can absorb this at low RPM. Once you are off by too many teeth though, things hit limits and valves bend, if not worse. To be honest, that is sort of what it sounds like is going on in your video, especially given the amount of shaved aluminum in the oil. Sorry to be a debbie-downer. Fingers are crossed that I am massively wrong.

In that case that the engine is basically toast. Used M42's are fairly cheap and easy to swap. Also, for less than $2000 you could probably have a nice OEM rebuild of the head and bottom end done, which would allow you to address this engine's biggest design flaws.
1) Upgrade to the 1994-1995 M42 timing case which uses a plastic guide instead of that awful deflector sprocket (direct bolt-in as long as you get all of the updated gaskets that go with it, check RealOEM)
2) Install a full 360 degree thrust bearing on the crank since the stock half-shell is weak BS (incidentally, NEVER start the car with the clutch pedal pressed in).
3) Make sure that the oil pressure regulator assembly in the bottom of the timing case is the newest design which is not prone to seizure like the original one.

Good luck, let us know what you find.

Crazy dude!
Thanks for the awesome info. I'm gonna read it a few more times and analize what I'll be looking for when I start taking things apart. The initial sound did indeed sound a bit like a diesel truck. But It also had more clanking to it.

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[bmwman91]

Can you expand on this?

I thought the purpose of putting the tensioner in a vice and compressing it was to aid in the ease of installation. If not compressed when installing, the tensioner starts pushing on the guide rail making it difficult but not impossible to get the the threads started in the head.

Correct, installing it compressed is only to make it easier to get the cap threaded on. But, remember that the way you decompress it is to smack it so that the little internal snap ring lets go. The required "smack" inside the engine comes from the loose chain whipping against the tensioner rail, which eventually hits the piston and frees it. That is, in my opinion, highly undesirable. Yeah, installing it uncompressed is extra work, but it is a hell of a lot less work than a full rebuild.




Musij, I also saw the thread you have going on M42Club. Yeah, if the "sand" in the oil is copper colored, then it is probably bearings. But for now I am sticking with my timing case hypothesis.