The tensioner is brand new and I'd rather know how it works than just throw another one in besides the fact that I have already dumped way more money into this project than any sane person would.

__________________
1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?

Its pin is spring loaded.

Then after you prime it, it is a fluid filled shock absorber.

Thus, it is harder to push down since you are fighting the spring and the fluid pressure

There is no reason to open it except out of curiosity, inspection or to drain it.

Good to know, I won't bother trying to open it up.

I'm not sure I understand the ratcheting function though, I don't see how it would work with the priming procedure as the plunger would simply get stuck in the retracted position.

__________________
1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?

Chances are your models tensioner has no ratcheting ability. The early ones did not for many years than the feature appeared. I was not aware it was discontinued for whatever reason as it seemed logical.

Basically if the tensioner failed or recieved no oil pressure from the feed passage it could not retract enough because of the ratcheting function to leave a very loose chain running.

This meant you had to extract the rachet from the front of the tensioner by pushing it through and reinsert it again from the back. Then extend it or perhaps the oil pressure did. The new chain being shorter in length meant the tensioner was extended out further than needed for the new chain when removed from the old chain.

I suspect the ratchet part was introduced as there may have been difficulties pointing towards a failed tensioner. Why the feature appears to have been eliminated must be a story as well. The illustration posted did not show a ratcheting function involved in that tensioner that I noticed. So I have to assume the feature has been dropped.

I also posted a suggestion on your other thread to the effect that if the old tensioner was changed just as a preventative measure. Install the old one to see if the noise is gone. Also compare part numbers between the old and new.

That makes sense Barry.

If it failed then the plunger could not retract into the housing so that the chain wouldn't go slack.

Mine does not seem to have the ratcheting function.

I press the plunger all the way in, it pops back out.

It was preventative maintenance however my old tensioner is gone.

Another thing that seems a bit odd is that the FSM states to use a press to depress the plunger while it is in oil to prime it.

However I can easily depress the plunger without any assistance. Of course that won't help much because the noise shows up when I apply tension to the chain.

__________________
1987 300SDL 167k
1992 Volvo 740 140k
1990 Volvo 740 250k
1989 Volvo 240 269k

Anyone want to trade an old Volvo for an '87 300sdl?

Since you can easily hand press the plunger back in. How is it making chain tension when in position and the engine not running? Does the chain appear to be under reasonable tension with it installed?

I would think the plunger should push back by your description. . If no oil is escaping when you push the plunger back in it is not primed I would think.

It appears mercedes service information really wants it primed a certain way from your description. Or is there a chance the tensioner is bottoming out?

Since it appears that if you back the mounting bolts off a little it solves the problem. To eliminate that as a possibility you should be able to reach down with a long screwdriver and still be able to push it back further or retract it more if you wish. If it will not back off when bolted in the final position. Something is obviously wrong. Perhaps the tensioner is of the wrong length. Or chain is shorter than design. Although I think that unlikely.

You may have to add some more gaskets under the tensioner flange if the oil feed to the tensioner is not obstructed as a result. Sounds like something strange is going on with that tensioner. Verify the part number again for your engine.

My real tensioner time on mercedes unfortunatly goes back to the very early 60s gas models. You installed the tensioner in place and reached in with a long screwdriver and primed them up. I am sorry I have not dealt with your type tensioner before. I might have been able to help more if I had.