Timing chain rails M117 Replacing Rails???

[turtlern56]

Hi all,
I've got a 1972 280se 4.5
I've read and read about the procedure for doing the timing chain replacement. I'm fixing to attempt the chain and cam sprocket replacement. My question is... I've read and am going by Tomguys awesome detail that if your old rails are the aluminum backed original style it is highly recommended not to replace with the new white style.
Anything else dictate a replacement?? Slight grooving etc..
Does this apply to the tensioner rail as well??
Its like a clip on slider over an aluminum rail behind the tenioner?? Replace slider regardless??
All of mine appear to be the original type So i didn't order any. Also I'm confused about the tensioner itself. Its my understanding they shouldn't go bad. I'm scared now to start this procedure for fear I will get it all put together and have fragile rails or worn tensioner and/or slide and not be fixing my problem entirely. I realize there is a crank sprocket and more slides behind timing case tho. No issues other than just 10 degrees of stretch. 130,000 miles. I would just like to hear some other opinions. Like I've said I've read and read about this from several sources. They all talk of aging rather than mileage in regards of rails and replacement. Any feedback would be great!
I'm waiting to hear some before i start in case i need to order tensioner, slide, 3 top rails. Thanks again Kevin

[Graham]

Originally Posted by turtlern56

Hi all,
I've got a 1972 280se 4.5
I've read and read about the procedure for doing the timing chain replacement. I'm fixing to attempt the chain and cam sprocket replacement. My question is... I've read and am going by Tomguys awesome detail that if your old rails are the aluminum backed original style it is highly recommended not to replace with the new white style.
Anything else dictate a replacement?? Slight grooving etc..
Does this apply to the tensioner rail as well??
Its like a clip on slider over an aluminum rail behind the tenioner?? Replace slider regardless??
All of mine appear to be the original type So i didn't order any. Also I'm confused about the tensioner itself. Its my understanding they shouldn't go bad. I'm scared now to start this procedure for fear I will get it all put together and have fragile rails or worn tensioner and/or slide and not be fixing my problem entirely. I realize there is a crank sprocket and more slides behind timing case tho. No issues other than just 10 degrees of stretch. 130,000 miles. I would just like to hear some other opinions. Like I've said I've read and read about this from several sources. They all talk of aging rather than mileage in regards of rails and replacement. Any feedback would be great!
I'm waiting to hear some before i start in case i need to order tensioner, slide, 3 top rails. Thanks again Kevin

When my 72 350SL needed a new chain a few years ago, I had same question. An ex MB shop owner who I trust advised not to change the metal backed guides unless absolutely necessary. So we left them in - they actually look good with minimal wear.

I did replace the tensioner. They do fail and it is recommended to do it at same time. It is an easy job. When ordering, be careful to get the right part - the design was changed at some point.

[wbain5280]

You need to determine how loose the whole chain and guides are. First, rotate the engine so the timing marks align, Set the crank to 0 deg and mane sure the cam sprockets align with the marks on the first cam tower. Rotate the crank until they do align, if they do not. Read the number of degrees on the crank sprocket.

If the offset is 'excessive', first replace the guides. The plastic ones are fine but need to be periodically check. Use a small socket and a ling bolt to remove the pins that hold the top three short guides. Replace the chain tensioner guide. There is a bolt on the lower front cover and a small tube inside. The chain tensioner needs to be removed.

Once you have the guides replaced, check the offset and if not properly aligned, the chain needs to be replaced. Follow the procedures in Tomguys writeup. You can grind a link off and attach the new chain. Slowly rotate the engine by the cranks to feed in the new one and remove the old one. Use the supplied link to hook them together. Be aware you may need to replace the cam sprockets if the tips are sharp and not dull or squared off.

[turtlern56]

Originally Posted by Graham

When my 72 350SL needed a new chain a few years ago, I had same question. An ex MB shop owner who I trust advised not to change the metal backed guides unless absolutely necessary. So we left them in - they actually look good with minimal wear.

I did replace the tensioner. They do fail and it is recommended to do it at same time. It is an easy job. When ordering, be careful to get the right part - the design was changed at some point.

Thanks for the response. That was my first thought too but I didn't order new tensioner or new slide
Upper guides look ok but I could see a little wear on tensioner slide last time I looked. I don't want to have to tear into it but once bc she is my driver. I've noticed that I could only find the whole piece (tensioner rail) and not just the slider that clips on. But to recap a new tensioner, new rail a must?
Hmm I wonder if that cap for pin is accessible without removing alternator? I know you would have to remove to access the ones in the head for uppers. If y'all can't tell I'm a new owner but long time fan. :-)

[Tony H]

i used to own a Toyota pickup truck that I replaced the Timing chain on. There was a company that made steel timing chain guides with a hard rubber lining to replace the plastic ones. Very simple, very inexpensive and very good. Too bad nothing exists for the M116/117.

[Tomguy]

There was slight grooving in my rails. I had about 12° of stretch. I replaced my chain and tensioner rail and I had about 2° after. Most, if not all of the stretch is in the chain. Replacing a 400k interval maintenance item that never outright fails - just needs wear replacement - with a 100k interval maintenance item that can outright fail - doesn't make sense to me. Might as well replace the whole chain system with a belt.

I didn't replace my tensioner, I couldn't push it in by hand - when reinstalling, I had to use a longer bolt to get it started. I then used the other (original) bolt to further tighten, and then replaced the longer bolt with the original on that side, and tightened both down.

[turtlern56]

Originally Posted by Tomguy

There was slight grooving in my rails. I had about 12° of stretch. I replaced my chain and tensioner rail and I had about 2° after. Most, if not all of the stretch is in the chain. Replacing a 400k interval maintenance item that never outright fails - just needs wear replacement - with a 100k interval maintenance item that can outright fail - doesn't make sense to me. Might as well replace the whole chain system with a belt.

I didn't replace my tensioner, I couldn't push it in by hand - when reinstalling, I had to use a longer bolt to get it started. I then used the other (original) bolt to further tighten, and then replaced the longer bolt with the original on that side, and tightened both down.

Thanks Tomguy.
I just ordered new tensioner rail. So already have new sprockets, chain, cam oilers here now, and now new tensioner rail on the way. Just wanted to take care of all of it at once rather than back and forth with it. That makes me feel better to hear it from someone who knows. I just remember seeing noticeable grooves on that rail last time cam cover was off adjusting valves. I've learned so much from this forum.
New chain is fed in with chain tensioner in place correct??

One more thing...Any special care to cam position or holding while breaking lose sprocket bolt. I know to pull tensioner off and replace sprockets with old chain still on. I don't have air for my impact at my current location unfortunately, So any real way to screw that up?? I know to hold steady with screwdriver through sprocket but didn't know how tight it was torqued and scared of rotating too much. I've read lots where some use a hand compressor for valves (even shows a diagram to build your own) but i don't understand what exactly they are doing with it that would make it so much easier???
Thx
Kevin

[turtlern56]

Originally Posted by Tony H

i used to own a Toyota pickup truck that I replaced the Timing chain on. There was a company that made steel timing chain guides with a hard rubber lining to replace the plastic ones. Very simple, very inexpensive and very good. Too bad nothing exists for the M116/117.

If there was and they were good ones you know they would sell a tens of thousands of them. I would be interested for sure

[turtlern56]

Originally Posted by wbain5280

You need to determine how loose the whole chain and guides are. First, rotate the engine so the timing marks align, Set the crank to 0 deg and mane sure the cam sprockets align with the marks on the first cam tower. Rotate the crank until they do align, if they do not. Read the number of degrees on the crank sprocket.

If the offset is 'excessive', first replace the guides. The plastic ones are fine but need to be periodically check. Use a small socket and a ling bolt to remove the pins that hold the top three short guides. Replace the chain tensioner guide. There is a bolt on the lower front cover and a small tube inside. The chain tensioner needs to be removed.

Once you have the guides replaced, check the offset and if not properly aligned, the chain needs to be replaced. Follow the procedures in Tomguys writeup. You can grind a link off and attach the new chain. Slowly rotate the engine by the cranks to feed in the new one and remove the old one. Use the supplied link to hook them together. Be aware you may need to replace the cam sprockets if the tips are sharp and not dull or squared off.

Yes i've determined stretch by aligning and it was 10 degrees BTDC. The guides were my main concern bc mine appear to be original and I had heard not to exchange with new white plastic. The chain tensioner was also a concern as well as the rail. Tomguy makes reference to replacing it with a 100K model where as these are 400K and serviceable. I take it all the replacements are the new ratcheting type?? i dunno. To back track a little I've never seen it explained the way you do on interpreting stretch by replacing guides before chain but kinda makes sense.

[Tomguy]

Originally Posted by turtlern56

Thanks Tomguy.
I just ordered new tensioner rail. So already have new sprockets, chain, cam oilers here now, and now new tensioner rail on the way. Just wanted to take care of all of it at once rather than back and forth with it. That makes me feel better to hear it from someone who knows. I just remember seeing noticeable grooves on that rail last time cam cover was off adjusting valves. I've learned so much from this forum.
New chain is fed in with chain tensioner in place correct??

One more thing...Any special care to cam position or holding while breaking lose sprocket bolt. I know to pull tensioner off and replace sprockets with old chain still on. I don't have air for my impact at my current location unfortunately, So any real way to screw that up?? I know to hold steady with screwdriver through sprocket but didn't know how tight it was torqued and scared of rotating too much. I've read lots where some use a hand compressor for valves (even shows a diagram to build your own) but i don't understand what exactly they are doing with it that would make it so much easier???
Thx
Kevin

No special care needed. If you are doing the sprockets you'll probably wind up closer to 0° of stretch than I did with the old rails (since I kept the old sprockets). Easiest way to do them probably would be:
1) Set everything to TDC (old chain still on),
2) Remove the bolt on the driver's side (left engine, right from under the hood) keeping the engine @ TDC,
3) Grind off a link from the chain,
4) Remove old and replace the sprocket,
5) Use the master link with the new chain to reassemble,
6) Roll it around to the other side,
7) Loosen the tensioner, mark the sprocket & chain (so you don't lose place),
8) Remove the link (don't lose the clips!), then the old sprocket and replace),
9) Replace the tensioner rail,
10) Attach the new chain to the leading edge of the old one and attach the trailing edge of the old chain to the sprocket with a small vice grip like in my guide,
11) Reinstall the tensioner,
12) Feed in the new chain, remove the link from the old and link up the 2 ends of the new.
13) When done, have some ice cold beer!

That's how I'd do it.

[werminghausen]

I had the same question because I am changing the cylinder heads on my 3.5.
I will change the rails even if they are aluminum/rubber, but they are worn.
I 'll also change the pad on the tensioner rail (these are cheap and available at Classic Center) or order a new rail.
This one will be hard to change I think with the head in place.

When I did the timing chain a year ago (yes I am there again) I had still approx 4 degrees retard after chain change. I ended up using an offset key. Maybe with the new rails and new sprockets the retard will be better. I'll see.
Martin

[Tomguy]

I've personally seen no less than 10 m116 and m117 engines in the junkyard with dead engines due to a snapped plastic rail. I've NEVER seen one in the junkyard with metal rails have a dead engine. That's enough for me to keep the older worn rails. I'd rather have a worn gold ring than a brand new plastic one.

[JamesDean]

Originally Posted by Tony H

i used to own a Toyota pickup truck that I replaced the Timing chain on. There was a company that made steel timing chain guides with a hard rubber lining to replace the plastic ones. Very simple, very inexpensive and very good. Too bad nothing exists for the M116/117.

But there is!

For the m116, meyle makes metal backed ones:


For the m117, an Australian company makes heavy duty plastic ones made from a material called Pactene I believe. However, they seem to be rather pricey.



Australia's leading Mercedes-Benz website

[werminghausen]

Originally Posted by Tomguy

I've personally seen no less than 10 m116 and m117 engines in the junkyard with dead engines due to a snapped plastic rail. I've NEVER seen one in the junkyard with metal rails have a dead engine. That's enough for me to keep the older worn rails. I'd rather have a worn gold ring than a brand new plastic one.

Hi Tomguy,
fair statement, if I change the rails for a plastic one I'll plan to change them within 10 years. That is about the time they should hold and not kill the engine?
I'll see if the new plastic one have an advantage regarding accuracy of valve timing. If not I'll switch back to the old worn ones...
Isn't there a replacement pad for the aluminum rails as there is for the tensioner rail from MB?
Martin

[Tomguy]

There were rubber replacements for the aluminum rails. You can call the classic center & see if they still have them.