RE: 1987 300TDT - Does anyone know if it's possible to just replace the timing chain tensioner and seal (oil is slipping by it causing a mess on the alternator etc.) without touching/altering the timing chain or timing in general? Is it a simple removal and reinstallation?

Why replace the tensioner if all you need is a new seal?

It's a straightforward removal and replacement but you have to install the tensioner in the relaxed position since it's a ratcheting tensioner than only gets tighter. I think it requires torquing a 14mm hex bit or something like that.

Sixto
95 S420
87 300SDL

Oh, didn't know that. So it is possible to just replace the seal without reinventing the wheel or causing any damage to the timing chain or the timing in general?

I quoted some M103 steps. The OM603 tensioner is simpler. Remove it by turning the big nut (24mm?), replace the crush washer, refit the tensioner and torque to 65 Nm. The manual talks about filling the tensioner with SAE 10 oil but if you keep it level and don't compress it while it's out it should be safe to put it back without further attention.

Sixto
95 S420
87 300SDL

I've had my tensioner out several times, at least six times, and have never had any problem related with it. I just unscrew it and lay it off to the side and then reinstall and tighten. My crush washer has never been replaced when doing this and forms a perfect seal every time. Maybe all that might be necessary for you is to tighten it, as it may just be loose, or looser than than should be!

I read in the manual, when replacing the chain tensioner, make sure the fly wheel pointer is at 0 T.

Does this apply in all instances ?


Please pipe in.

All the times I've had my tensioner out was for removing the cam, and the cam does have to be in a specific position with two lines lining up for removal. You cannot remove the cam without first removing the tensioner. No specifics are given in the Service Manual with respect to a specific procedure for removal of the tensioner for the purpose of removing the cam. This is in referance to the 603, not 617, or whatever OM engine!

No mention of that requriement in section 05-310 of the 603.960/1 manual.

Sixto
95 S420
87 300SDL

05-310 of the 620 Manual - Removal and Installation of Chain Tensioner.

Look at the accompanying pic.

So the $64 question - if the cam marks line up and the flywheel shows 1 - 1.5 deg off, which is more important when replacing the chain tensioner - the cam marks lineup or the flywheel at 0T ???

05-310 of the 602 Manual.

Sorry for the typo.

As I've mentioned, I have never had any problems with my chain tensioner out while accessing my cam, nor have I heard of such. I wouldn't worry too much about it, but maybe I've just been lucky, or 1 to 1-1/2 degrees out is not critical!

db, alignment of the cam marks is relative to the crank pulley. At some point in the rotation the crank pulley will be at 0T and at some point the cam marks will align. Hopefully both occur at the same time. For the most part this is determined by the length of the chain. There are other factors such as wear in the sprockets and thickness of the head gasket. Given all that, it's a wonder that on an engine with over 100, 200 or 300K miles you can get everything to align to within 1 degree without 'cheats' like offset keys.

Having said all that, I don't follow your question The tensioner has nothing to do with static cam timing. Its job is to keep the chain taut so the crank can pull the IP and cam without the jerkiness associated with the natural rest positions. It's also there to take up the slack designed into the timing system to allow the engine to be serviced without breaking the chain.

Sixto
95 S420
87 300SDL

Which of the two hex heads on the tensioner do you loosen/remove to take the tensioner out to replace the gasket? Never done a timing chain before, so I'm a little unsure about this...

The big hex that takes a 32mm socket.

Sixto
95 S420
87 300SDL

So I just unscrew it, carefully back it out without tipping it and put the new crush washer on and screw it back in. Thanks.