I am replacing the gasket on the upper timing cover on my 91 300Ce with a m104 engine. My question is, do I need to remove the chain tensioner to pull the front upper cover as it has a small chain guide located between the 2 cams. It looks to me like it is held in place on two sliding pins and seems like it will just come off.

Antonino

I wrote all the following and then realized your 104 may not be the same as mine. (I have the 104.992) There could be a difference in the guides/tensioning arrangement. Typing is all already done so I'll go ahead and post anyway.......


It is not necessary to remove the tensioner--the upper chain guide will easily slide off the two pins on the upper timing cover. No retaining devices are employed. (there are circumstances where you will definately need to remove the tensioner--keep reading below)

An additional tip--You will find it much easier to remove/reinstall the upper timing cover if you remove the pin that holds the intake cam side chain guide. The pin is accessable by removing the small round pin cover located about halfway down the upper chain cover on the drivers side. If I remember correctly, It takes a 5mm allen wrench. The pin has an M6x1 (again, if memory serves me correctly) threaded hole in the end. A slide hammer can be threaded into the pin to facilitate removal. If you don't have a slide hammer, you can use a bolt with a deep socket and some washers to make a "pin puller". I used one of the bolts that holds the valve cover down--same threads as the pin. Just ensure you have enough of the threads engaged in the pin to prevent stripping. You can back the pin out slightly by turning the bolt, then add another washer or two, reinsert and tighten again........It takes a little fiddling to get the right amount on thread insertion and still have some thread depth left to tighten the bolt and pull the pin. (if you are at all unsure about this process get help--you don't want to strip the threads out of the pin.)

When you reinstall the cover, care is required to prevent "rolling" the new U shaped seal. (probably the reason you are doing this in the first place.) If you try to reinstall the cover with the pin already in place, it is almost impossible to not roll the seal.

A little more about the tensioner. It has an internal ratchet mechanism. If you allow slack in the timing chain, (either by removing chain guides or cam sprockets) it could "ratchet up" to remove the slack. If you don't "zero out" the tensioner during reassembly, you can end up with an "over tensioned" chain. This will most likely cause timing component damge. If you follow my recommedation of removing the pin, you WILL NEED TO ZERO OUT THE TENSIONER RATCHET. Removing the pin could allow the intake side chain guide to move out enough to allow the tensioner pin to ratchet out a click. If you then reinsert the pin it could be possible to "over tension" the chain.

To zero out the tensioner, it must be removed and the plunger pin must be reinserted from the outside of the tensioner. You should probably consult a service manual for the exact procedure.

By the way, I assume you read this:

http://www.peachparts.com/Wikka/M104HeadGasket

Dear van Swaay, I managed to get the cover off as the pins holding the top rail are not threaded and the guide just slides on and off...however, upon removing the cover I realized that the left rail that is pushed on by the tensioner, original alluminum backed with plastic surface that the chain rides on has some chips on the plastic edge...I posted a new thread asking for advise.

Antonino