'90 300E 3.0L engine timing chain tension - PeachParts Mercedes-Benz Forum

Andy_M · #1 09-06-2007, 02:52 PM

Just got the rebuilt head back and am putting the engine back together now. I have a question on the timing chain tension.

During the disassembly process we took the gear off the cam and bungied it to make sure that the tension was maintained and the chain didn't move. That worked out fine, but the timing chain tensioner seemed to creep out a bit, putting more tension on the chain. I removed the cover plate and spring to try and move it back (you could plainly see the oil line on the plunger cylinder) but it would not move back to where it was without adjusting the bottoming ring outwards just a bit to slacken it back to where it was. I had to slacken it just a tad in order to get the gear back on the cam correctly (don't worry, we marked everything very well before removal.)

Now I am wondering what is the correct amount of tension to have on the chain before I close the cover up. Can anyone give me an idea how tight the chain should be before I close up the cover ?

S-Class Guru · #2 09-06-2007, 03:59 PM

Hmmm, I have a '91 300SE with the 103 engine - I suppose that is the same motor you have. My tensioner is not oil pressurized, just spring loaded.
The way it works is: there is a pin inside the plunger that is spring loaded. It has little grooves in it that allow it to move inward only, when it reaches the next groove it cannot move back outward again (sorta like a plastic tie-wrap). As the chain stretches, the tensioner plunger clicks inward, tightening the chain, but cannot move outward again to allow any chain slack.
if you removed the chain without taking the tensioner spring out, the tensioner plunger clicked all the way in, and cannot be forced back.
The only way to reset the tensioner is to remove it, remove the plunger, and reinsert it again from the other end.
Hard to describe, but very obvious when you get the tensioner out and apart.
Just take a big allen wrench and loosen the tensioner outer bolt, it will all come out easily. getting the spring basck in is not fun, but can be done with some patience.

This all assumes you have the 103 engine with the spring loaded tensioner.
If you have a big allen-head cap, about 10-12mm, holding it in, then it's probably like mine.

DG

Andy_M · #3 09-07-2007, 09:31 AM

Sounds like the same mechanism....and that is exactly what happened, the adjuster ratcheted out about 1/8" (probably 1 groove). Thinking that we had to remove the spring pressure, we removed the outer retainer cover with a large allen head and removed the spring, but discovered that the tensioner would still not move back.