M117.968 Timing Chain Q's - (Steve, Gilly??)
 

I'm about to have some extra free time on my hands thanks my company's closure of the plant where I've been working :( and am considering replacing the timing chain in my '87 560SEL. After several sessions of searching through the posts here as well as looking at the MB service CD, I have a general idea of the various aspects of the job but keep coming up with more questions, especially as I read the various suggestions and opinions on the board. :confused:

With that in mind, I'd like to appeal to the helpful side of Steve B., Gilly, and any other professional techs we are so fortunate to have amongst us for some thoughts and advice. The questions that keep coming up in my mind are (in no particular order):

1. How critical is chain replacement on these engines? Mine is not the original for the car and is probably at around 115K. I've run into several threads that treat replacement every 100K as gospel but a few others that indicate no problems well beyond that mileage, except for some engines with single row chains (all diesels??).

2. Some posts here seem to indicate that the more troublesome parts are actually the plastic chain guides rather than the chain itself. Is this really the case and, are the three top guides in the heads really the bigger problem or should the bottom ones be done as well? (The simple question is, can I use the feed-the-chain-in-from-the-top method or do really need to strip the front of the engine and pull the timing cover?)

3. Today I stumbled on a thread dealing with the merits of one piece endless chains vs those with master links. Is there a significant difference between these from QUALITY manufacturers? (Has anyone dealt with IWIS brand chains?)

4. On a related note, I will replace the valve stem seals at the same time. Do I need to buy/rent the MB valve spring compression tool to do this job or will a conventional tool work? (Any suggestions for conventional tool brands?)

Thanks for everyone's help in the past and in the future. This forum continues to be educational and entertaining. While I've done plenty of wrenching in the past - rebuilt a couple of Chrysler V-8s - this will be the first time for such major work on the car I use as a daily driver. More importantly, this will be the first time with a wife around who won't be very understanding if my attempt at saving money by DIY on a PM type project ends up costing a lot more by accident, especially given my unemployment. :D

jlc

plastic chain rails are 99% of problems when the valves bend. usually on the drivers side. the rail brakes & gets dragged along with the chain & then jamms between the chain & gear. chains & cam gears should be changed if cam timing is not aligned. iwis is a very good chain. i only have the mb spring compression tool, so i can't answer that ?. hope this helps.

The chains do stretch on these M116 and M117 engines over time, because the chains are long and change direction many times as they travel from the crank at the bottom up to each cam on each side of the "V".

Most members and techs on this site recommend replacing the chains approximately every 100,000 - 120,000 miles. 4 degrees of stretch is considered the time to change the chain.

Further, it's not just the chain that's the problem. The chain guide rails are made of plastic, and become hard and brittle over time, as well. As the chain stretches it becomes loose, and starts to rattle and bang and slap against the guides. It usually happens at start-up, but when the chain gets loose enough and the guide rails are old and brittle enough, the chain will slap against the plastic and it'll break apart. Plastic pieces will get stuck in the chain and the sprocket, and bam!, you've bent a camshaft, pistons will hit valves, etc.

I've found from reading posts on this site, that's it's more often a loose chain breaking old guide rails, than a loose chain jumping a sprocket that causes an engine failure.

Either way, your car is due for a timing chain replacement and upper guide rails.

Just like Nike says, Do it. Do it now.

Although not a tech, MikeTangas is a very proficient mechanic, and he did this whole procedure on his '86 560 SEL, and posted pictures along the way. He did it about a year ago, so you might try searching for the threads under his user name.

You might also try e-mailing him. He's very helpful with others on this forum.

Replacing the three top rails DOESN'T require the front of the motor to be taken apart. Simply remove the P/S pump and bracket on the left side and the alternator/ air pump bracket on the right side. This will allow easy access to the pressed-in pins which secure the rails. As a rule of thumb, the darker brown the rails are the closer they are to ruining your day. They can be seen with the valve covers off. This job is a lot easier than it appears to be.

I just did cover off timing chain job on my 86 Euro 500 Se(420)Euro engine.The larger bottom rail had deep groves in it was so thin could almost see through it ,all the rails were badly worn, they had 94 stamped on them so guess they were 8 years old.Also changed oil pump chain while had it that far apart.was a time consuming job but feel much better having all new rails as don't know how many miles are on this replacement engine.It runs strong burns no oil,oil is still clean after 1200 miles since change........
William Rogers......

Thanks
 

Thanks Guys. I knew I'd get some succinct advice from folks here.

Paul S. => Thanks for the pointer to Mike Tangas' thread. I recall seeing that last spring but never getting far enough into it to realize that he had done chain work as well. I've now printed the whole thing out for reference.

Mike (if you're reading this) WOW!! My hat's off to you for all the work and for caring. From the looks of the pictures your car and mine are nearly identical except for interior color (mine's navy blue) and year (86 vs 87). I may ask you some specific questions as I get into this project.

Right now I'm planning on pulling the valve covers this weekend just on the very remote chance that the guides were replaced by the PO or prior to the engine being installed into this car. Since this was a replacement engine, all I know is the approximate mileage at the time it was installed. I don't know what, if any, PM work was done to it as part of that process. While I strongly expect to find amber or darker guides, I'd rather not take the time doing all of this research and purchasing of parts only to open things up and find the job doesn't need to be done.

Hey - one can hope, can't one? :rolleyes:

jlc