190E 16V Timing Chain Tensioner
 

I just replaced the timing chain tensioner on my 1987 190E 16V with the upgraded model available from Mercedes. Prior to the change I checked chain stretch at something very close to only 1 degree. The chain was tight over and between both cam sprockets with the original tensioner and the engine turned off. The chain is much looser now between the cam sprockets with the new tensioner installed. I have not turned the engine over until I understand why the chain would be looser.

Could the chain have jumped a tooth on one of the camshaft sprockets when the old tensioner was released? If yes, I would guess most likely on the exhaust cam since it sits right above the tensioner. Does the upgraded tensioner work with hydraulic pressure, in which case I would have none since the engine has not been started with the new tensioner installed?

Any information would be appreciated.

Jim Herold

Firstly, I do not know this engine, I recently changed out my 560's tensioner. The old (19 year old/88K mi) unit was definitely lacking springiness and would not hold tension for long.

The one I put in (febi or iwis, I forget) was in a box marked "this side up" (like, this was remotely likely to have been adhered to from the factory to my door), in a sealed bag, and the bag was partially filled with oil.

After doing some research, I determined that the unit was shipped fully charged with oil and some had leaked out. I refilled it with oil through the hole, and pumped it until it was almost uncollapsible. In this condition, it could not be installed, so I cautiously pushed the punger in a little at a time, releasing oil through the relief valve, until I could get a few threads each of the screws caught to install it, and then screwed in the two mounting screws evenly, a turn or two at a time. With this, my chain was tight when I cranked over the engine (by hand) a few times before final reassembly and normal start.

I did this because of paranoia about what would happen in the first few seconds of start-up. Was it necessary...I don't know...but it didn't hurt. But considering that a mistake is very, very expensive, I think a little paranoia is in order!

IF your tensioner is hydraulic (as opposed to the ratchet type), you might be able to do this also, but again, I'm not exactly sure about the construction of your particular engine.

This is kind of a hard one to discribe because I dont want to tell you its ok because of the possible problems if its not. I would start buy making sure the (two) dots one on each cam gear are lined up with the horizontal plane of the top head surface.

The cam gears are suseptable to movement because of the cam lobes are not all at TDC. So with the old tentioner out the gear may have rotated a little bit.
The tentioner has a spring that moves it out to the next step(new style) and that spring may not have enough tention on it to rotate the exh. cam back to its needed position.

The updated tentioner has step index's on the side of it to stop the tentioner from retracting when there is low or no oil presure.

So what I am getting at is that if the crank is still at TDC and the intake cam mark looks ok and the exh. cam is just a bit to far clockwise then you can just remove the tentioner cover cap and rotate the cam back and push the tentioner piston farther in. (WARNING ! JUST ENOUGH TO TAKE UP THE SLACK AND NO MORE)

I tried to make this as understandable as possible, but some times its a bit tricky not knowing another persons skill level. So if it doesn't make sense to you maybe see if others post or have some one that has a good knowlage of engine mechanicals give you some advice in person. This is not an area you want to have a problem in, but I think you already know that.

Good luck Jim..........and feel free to ask more this is a great forum with a lot of great members.

Dave..................

Dave,

Your post was very clear and described one of the possible reasons I had thought of causing the slack in the chain between the two cam sprockets.

Question: I did not set the engine to TDC before I started this process. If I remove the spark plugs and rotate the engine by hand to TDC using the crankshaft damper bolt, can the cam timing get out of alignment any further than the slight amount it might be? I would think not, but I want to play it safe.

Also, if I have turn bring the exhaust cam counterclockwise a hair, any harm done if I turn it back from the current position just to see if the tensioner pops into place?

Thank you for your response--I'm sure this is the cause of the problem

Jim

Its ok that your not at TDC at this point as long as the crank and intake cam have not ratated and they prob. haven't. The good thing is only at TDC mark 0 and at 180 are there actualy pistons up at the top of any of the cylinders.

Because your exh. cam has gone clockwise. Holding the crankshaft in its present position and rotating the exh. cam counter clockwise to take up the chain slack will only move it closer to the correct cam timing and with the chain on you cant over rotate it so I would just have someone hold a socket on the crank to stop it from rotating counter clockwise, and rotate the exh. cam counter clockwise and listen for a click noise from the tentioner. Doing it this way will remove any slack from the rite side and put it between the exh. cam and the crank with the tentioner between those two.

If you dont hear a click or it doesn't seem to take up the slack give the tentioner rail a little push with your finger.
You just don't want to pry it with a lot of force as that may move to tentioner up to an index that is to tight and couse premature wear to the guides.

Hope that helps and will be waiting for the good news.

Dave..................

It seems to me you are worrying about an effect that will be taken care of by the chain tensioner. When you took the old one out, the exhaust cam was free to rotate toward the intake cam, and it did, slightly. You can probably manually push it back (there are some flats behind the camshaft sprockets that you can get a Cresent wrench on and turn the camshaft as far as the chain slack between the two sprockets will allow), or, you can start the car and the oil pressure will apply a load to the chain tensioner so it tensions the chain. Once the slack between the two sprockets is gone, with the new chain tensioner, it stays gone. The old ones would allow slack, as you describe, once the oil pressure decayed after shutting down the engine. As the chain stretched over time, this became a bigger and bigger problem. Thus the new chain tensioner with the mechanical ratcheting feature. Good luck, Jim

Job successfully completed. I pulled the spark plugs and turned the exhaust cam counterclockwise using the flats on the backside of the sprocket just enough to remove the slack in the chain between the camshafts. The exhaust cam stayed in postion without my doing anything to the newly installed tensioner. The intake cam never moved. I then turned the engine over by hand several revolutions from the crankshaft bolt and the chain snugged up even further. I lined up the cams and checked for TDC, which looked good. Ran perfectly when started.

Thanks to everybody for the advice. I was admittedly overly cautious because of the damage potential from a mistake.

Thanks again!

I, for one, do not think you can be overcautious in this area. The financial damage from a mistake doing mine would have been serious - but not as bad as the damage inflicted upone me hearing about it for the remainder of my life from my Financial Manager (wife).

Great news.
Happy motoring.