OM642 Timing Chain Woes

[OJLane]

I have recently had the dreaded two second chain rattle on my OM642 (E350 CDI) but after the two seconds it would run sweet as a nut. I did some reading figured it couldn't hurt to change the tensioner, so after making the trip in my wife's car to the local dealer, replaced the tensioner (the old one just fell to bits as soon as it came out so I presume it was knacked).

When I then tried to run the engine it initially wouldn't start but then sprang to life, this is when my issues started! It appears to be running on all cylinders however doesn't appear to be as smooth as it was although I can't really tell with the new noises, the chain now rattles all the way around and there is now a squeak at the front of the engine.

1. Could I have skipped a tooth by replacing the tensioner?

2. Could something have come loose around the chain causing it to loosen?

I can see the oil hole on the tensioner which I believe means the chain is no longer tight, I gather I will have to replace the chain but I see no point in doing the usual pull through method if a tooth has skipped or if something has dis-lodged inside. Have I missed something? I would love to be able to take it to my local specialist but unfortunately the way things are currently this would not be possible :-(

 

[mersum1es]

1&2 I doubt.

Your chain probably IS tight, but it means that tensioner must be extracted to get it tight. Stretched chain means few degrees offset in timing, which may cause uneven idle, just I don't know why old tensioner did help there.

Timing chain is measured according the WIS by MB own tool which is put in place of the tensioner. I can't remember if OM642 timing can be checked without opening engine.

 

[OJLane]

1&2 I doubt.

Your chain probably IS tight, but it means that tensioner must be extracted to get it tight. Stretched chain means few degrees offset in timing, which may cause uneven idle, just I don't know why old tensioner did help there.

Timing chain is measured according the WIS by MB own tool which is put in place of the tensioner. I can't remember if OM642 timing can be checked without opening engine.

Thank you for your reply, it turns out as I suspected that the chain was loose and must have stretched quite a bit! When I took the old tensioner out it fell to bits, I had a thought this morning that the new tensioner was not taking up all of the slack because the piston was not expanding past it's limits which the old one was. I then put the old one back in and my thought was proven, the chain rattle has gone! I just need to change the chain now as I was unaware that it had stretched so much :-[

 

[zoomer46]

oj , can you tell me the mileage on your engine when this happened ?

and what is the average life of a cam chain on an om642?

 

[TeddyRuxpin]

Didn't think this was a 'thing' on the OM642

 

[W1ghty]

oj , can you tell me the mileage on your engine when this happened ?

and what is the average life of a cam chain on an om642?

Very long buddy , it’s not something that comes up on the forums

 

[mersum1es]

It was. They are 'all' stretched later or sooner. Those pics show it clearly. I have changed both my OM642 chains (200k+ km)

OM642 jakoketjun venymä - Sivu 3 - mese.fi

 

[zoomer46]

cheers,
i know on the audi v6 tdi they are expected to be changed at a certain mileage regardless so was thinking if it applies to the om642,
well.... my e350 cdi SOMETIMES has a timing chain cackle on cold start up ,
but when warmed up it is perfect,
i would say 50% of the time from cold there is no noise,
i'm thinking its possibly the tensioner is worn so i'm thinking of replacing it.
is that a fair assumption?

 

[mersum1es]

Nope, just tensioner change won't help. Can you see tensioner via oli filler hole? Later OM642 this is not possible.

Good thing is that there are not drastic feilures reported of OM642 regarding chain/tesnioner issues. Evidently it holds it place very well, but couple of mechanics have said that tension was so extracted that when they removed it, it dropped to pieces because adjust was so outstretched.

 

[W1ghty]

1&2 I doubt.

Your chain probably IS tight, but it means that tensioner must be extracted to get it tight. Stretched chain means few degrees offset in timing, which may cause uneven idle, just I don't know why old tensioner did help there.

Timing chain is measured according the WIS by MB own tool which is put in place of the tensioner. I can't remember if OM642 timing can be checked without opening engine.

What mileage is the car on buddy ?

 

[W1ghty]

I thought I would go and check my OM642 . The engine is on 114,000 miles . The tensioner looks to be 4 threads exposed .
So how many threads are there and what is considered time to change the chain ?
Ive got no noises or issues , just curious

 

[W1ghty]

Just reading a bit more on tinternet , it’s not the number of threads exposed , it’s more to do with the piston extension .
Some reports saying that if the tensioner is changed early before any decent chain stretch then this will benefit the engine .

 

[mersum1es]

Just reading a bit more on tinternet , it’s not the number of threads exposed , it’s more to do with the piston extension .
Some reports saying that if the tensioner is changed early before any decent chain stretch then this will benefit the engine .

Oil holes of piston shaft are a good indicator. If you see them, change the chain. Just note the shaft could in position where they are not (clearly) visible.

 

[W1ghty]

Oil holes of piston shaft are a good indicator. If you see them, change the chain. Just note the shaft could in position where they are not (clearly) visible.

I had read that as well , thanks buddy . Sounds like a summer job …..maybe

 

[Carrotchomper]

Hi folks, annoyingly I think I may have to tackle this job soon… Rattle (especially when cold) for a couple of seconds then it settles down. Has only started happening in the past couple of weeks.

Is this the kind of job that a decent independent garage would be able to do or is it potentially a Merc specialist job?

What sort of labour are we looking at? Hoping that tensioner might solve it but how much for this and chain replacement? Eek