M117 timing chain.

[SickFinga]

Does this mean that the bottom sprockets are worn out too and are in the worse condition since they work twice as much?

[Mike D]

Nope. The crank gear is much harder and I don't think I've ever seen one worn out. Different type of pressure on it also.

[SickFinga]

Originally Posted by Mike D

Nope. The crank gear is much harder and I don't think I've ever seen one worn out. Different type of pressure on it also.

What about the idler gear?
By the way, is there a gasket that goes between the timing case cover and the cylinder block? Can't find it in the parts catalog.

[Mike D]

It's unusual for the idler gear to be bad. Upon occasion, in the case of low oil levels, I've seen the center bearing surface galled but the idler doesn't really have any pressure on it. Inspect before replacing is the best advice I can give you.

[merchauser]

why should you not use the plastic rails? i just ordered all new rails from the MB dealer; are the factory parts all plastic? where do you get the aluminum ones and why use them?

[Mike D]

Plastic + drastic temperature changes + being immersed in hot oil + constant stress levels at varying speed = bad things gonna happen, eventually.

The aluminum ones are more durable.

To the best of my knowledge (the only way I've ever seen them) aluminum guides were installed only on the earlier engines. Much like the case of the old American timing gears reversed. Detroit used the plastic gears because they were quieter. Benz switched to the plastic guides for the same reason.

[Strife]

Originally Posted by Mike D

Nope. The crank gear is much harder and I don't think I've ever seen one worn out. Different type of pressure on it also.

I have one with an unknown number of miles on it (probably 80-120K) that has noticeably asymmetrical teeth. Of course, I don't know the maintenance history of the engine either

[SickFinga]

Replaced timing the chain, tensioner, tightening lever, cam sprockets and here are the results.

Set to 0 degrees


driver's side bank looks good


passenger side bank if slightly off


from looking at the woodruff key it looked like an offset one. Should I change it?

P.S. The timing chain I got from Mercedes was stamped with JWIS logo.

[Mike D]

If it is the offset then I would change it. The variance you are showing is acceptable. If removing the key zeros it then well and fine. Don't be surprised if it errs in the other direction.

There is a difference between "worn" and "worn out". As a for instance, I've got a lot of wear but I don't think I'm worn out, yet.

[GGR]

Well done.

Usually up to 2-3 degrees advance on the passenger side camshaft is acceptable as it is going to correct itself with wear. It's not uncommon to to have it retard with a new chain, especially if your heads have been surfaced in the past. I would try turning the offset woodruf key by 180 degrees (switch the offset side) and see how it is. You just need to take the tensioner out and unbolt the sprocket. Don't forget to put a rag in the chain well while doing this, you don't want anything to fall in there).

By how many degrees are you off? If you need to buy an offset key keep in mind that the value is for the cam, not the crank (ie a 2 degrees offset key will read 4 degrees offset at the crank).

Did you compare the two chains to see how much stretch you had?

[Tomguy]

That looks like 2-3° of retard if I am not mistaken. Which is probably unavoidable, I'd say that's acceptable.

[earnest37]

Got an "engine in a bucket" job from my daughter and son-in-law. It is an '85 380SL with only 85k. They had a "mechanic" pull the engine, removed the heads, cams, etc. I now have it in my home shop/garage. Something happened to the cam drive setup which bent nearly every valve on the driver's side head. Had both heads reworked at a very reputable shop. Replaced all eight valves in the one head and all 16 valve guides. Heads were both milled about .003". The intermediate gear for the timing chain had a broken tooth and the return gear was slightly worn so I've ordered both new from MB. The timing chain looks good but might replace it depending upon professional advice. I've got all six new chain ramps - three in the heads and three behind the timing chain cover. Also replacing the chain tensioner on the oil pump chain. I have a printed manual which covers just about everything I need except how to align the cams for proper timing. The manual says to mark the chain and cam gears before removing them. This was not done before they were previously removed and I'm way beyond that since I essentially got this engine in parts. Anyone know of a simple, but "perfect" method of timing the cams in this engine? Expert help greatly appreciated.

[Tomguy]

You don't say if the heads & cams are already mounted - I assume they are or you would probably not be asking, since you'd set the crank to TDC & "Go with it", setting the cams to TDC to match.

Remove all the rockers. This will let you turn the crank to TDC without interference, then move the cams to TDC & connect the chain. Remember, the chain needs to be tight on the leading edge (the right side of each cam) so you may need to turn the cams backwards slightly as you put the chain on each cam sprocket. Then reassemble the rockers.

[PanzerSD]

Originally Posted by Tomguy

If you're super-picky about it you can use them but the real point was when rebuilding an engine or redoing valves, say you need to shave down the head - this means less chain is between the cam and crank, and even moreso on the right (passenger) side. The issue you'll run into not having everything torn down & on a stand is that you won't know which key (if any) you need until everything's replaced, then you will need to undo the chain, pop off the cam, put in the key(s), etc. When I rolled my new chain in I had 3° of stretch on my original (aluminum-backed) rails. Which brings up another point / question:

I can't see your rails in your pics. Are your 3 riding rails (not the tensioner one) aluminum-backed? If so I always suggest NOT replacing them with the newer-styled plastic ones.

Which sparks my question. My rails are of the plastic kind. I have an older engine (117.983) if those rails are aluminum backed, would it be a good idea to take those, since, I'm also taking the valve train and putting it on the .986?

[PanzerSD]

Originally Posted by Tomguy

You don't say if the heads & cams are already mounted - I assume they are or you would probably not be asking, since you'd set the crank to TDC & "Go with it", setting the cams to TDC to match.

Remove all the rockers. This will let you turn the crank to TDC without interference, then move the cams to TDC & connect the chain. Remember, the chain needs to be tight on the leading edge (the right side of each cam) so you may need to turn the cams backwards slightly as you put the chain on each cam sprocket. Then reassemble the rockers.

Also take out the spark plugs, or the compression will not allow you to turn the engine