M42 sounds like diesel

[bignslow]

I just finished replacing all gaskets on top end and a couple of timing chain guides. After putting the engine back together and firing it up it sounds like a diesel. Sound goes away above 2000 rpm but as soon as I drop the RPMs below 2k it comes back.


I did not replace the timing chain tensioner so that's one thing I am suspecting.


The other thing I read is my timing could be off if chain jumped a tooth. I did mark both cams and crank sprockets in relation to the chain and reinstalled in same order matching up the marks so I don't think it's that.


Is there anything that could be causing this?

[Sladek]

definitely off a tooth, happened when I did mine even when I thought everything was lined up right. make sure timing is good


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[bignslow]

So how would I verify if it's correct or off a tooth? Pull the valve cover, set engine at TDC and check alignment of the cams?

[hyperE30]

Chain guides sound loose

[jaredmac11]

Yea Im wondering about the chain tensioner. What did you do with that?

[roguetoaster]

As already stated, start with the chain tensioner. Move on from there to the more costly or problematic things.

[bignslow]

I pulled the valve cover off tonight and verified that timing is set correctly. When I pulled the tensioner out though it was seized. It is a newer style M44 tensioner so it's been previously replaced.

When I pried the piston out I noticed that the snap ring that goes around the end of the piston is what caused it to get seized inside. Is that snap ring suppose to be there or not? I read somewhere that the snap ring is only there for installation.

Regardless I have a new tensioner on order.

[bignslow]

It was the tensioner. I took the snap ring off and put it back in to test and it sounds fine now.

[bmwman91]

Is it the old/original design of tensioner? The one at the top is the old one, and BMW redesigned it later on because it would seize.

[bignslow]

Nope, it's the newer design.