M42 knocking sound help

[MBGold]

Hello,

My engine started making a very loud knocking sound.
It's a E36 M42. Hidraulic tensioner is new. i'm guessing bent valve, hydraulic lifter failure or maybe something worse..tell me what you think.
you can ear the sound here and here

[jntar]

Could also be the rod bearings.

[MBGold]

humm, can easily test that...wait a minute.

[MBGold]

yeah probably...unplugging 4th cyl plug reduces almost all the knocking...
what could be the causes of this?

[roguetoaster]

Well, when you take the explosive load off of one cyl you change the way in which thrust is applied to the crank, right? So it could be anything from a bad crank/bottom end to a vibration dampener failure. I think a better clip without wind noise would really help.

[MBGold]

i've recorded another clip
check here

[bmwman91]

Does this noise start happening at ~3000RPM?

It is always a little hard to tell what exactly is going on from recordings, but this could be timing assembly related. Have you given the chain and guides a look? When was the tensioner last replaced?

A common fault on the M42 is the crank thrust bearing getting chewed up. Stock, the engine only has half of a thrust bearing shell, 180 degrees. It can wear out and leave you with a lot of crank end play. Can you check that?

I would drain the oil and see what is in it. I HIGHLY recommend getting a magnetic oil pan drain plug since it can provide some insight into wear, and prevent anything with iron in it from getting sucked into the pump.

[series88]

Can also be a bad oil pump or clogged pickup. My previous.m42 did the same. Oil is.not getting to the upper parts of the engine

[roguetoaster]

It sounds more like one cylinder is not firing to me than a rod/bearing issue. I would take the plugs out and inspect them. If it turns out that one is not firing (due to no spark) it's probably a coil or coil driver failure.

[MBGold]

i've replaced the tensioner maybe at 3000km/1800miles ago.
I've also replaced the timming cover gasket and when i did the guides looked ok.Even so i noticed some random rattle coming from the chain when i rev it hard, then it goes away. But now the sound is different.
Probably is the a rod bearing or crank bearing.Will get the oil pan out tomorrow and look into it.

[bmwman91]

It sounds more like one cylinder is not firing to me than a rod/bearing issue. I would take the plugs out and inspect them. If it turns out that one is not firing (due to no spark) it's probably a coil or coil driver failure.

I have had coils go out before. It doesn't make any weird noises, just runs like shit (on 3 cylinders).

i've replaced the tensioner maybe at 3000km/1800miles ago.
I've also replaced the timming cover gasket and when i did the guides looked ok.Even so i noticed some random rattle coming from the chain when i rev it hard, then it goes away. But now the sound is different.
Probably is the a rod bearing or crank bearing.Will get the oil pan out tomorrow and look into it.

Good idea. I wish we could give you happier answers, but bad mechanical noises from engines are usually due to bad mechanical things!

[MBGold]

Just to let you know that it was the 4th cyl. rod bearing smashed. The 2th cyl. was also bad.Engine with 95.000miles

Thanks,