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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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Discussion Starter #241 (Edited)
I think most folks just change the upper chain guide rails, as like you mentioned that the lower guides requires a lot more disassembly.
ALSO, there is yet another chain in there - a small single row chain that drives the Oil Pump. Its single row in ALL
Mercedes engines, but there is so little stress on it that its not an issue.

I read that the main reason for timing failure is those plastic guide rails which get brittle and break with age. Also have read that very early R107s had metal guide rails. Too bad those metal ones are not available.

The question that has never been answered is "Why did Mercedes go to the trouble to build a Single Row Timing Chain engine only for the USA market?" 380SLs for the rest of the world all incorporated dual row timing chains. There was cost and engineering to source not only a special chain but also single row sprockets, documentation, and inventory the special (shitty) parts.
 

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I think most folks just change the upper chain guide rails, as like you mentioned that the lower guides requires a lot more disassembly.
ALSO, there is yet another chain in there - a small single row chain that drives the Oil Pump. Its single row in ALL
Mercedes engines, but there is so little stress on it that its not an issue.

I read that the main reason for timing failure is those plastic guide rails which get brittle and break with age. Also have read that very early R107s had metal guide rails. Too bad those metal ones are not available.

The question that has never been answered is "Why did Mercedes go to the trouble to build a Single Row Timing Chain engine only for the USA market?" 380SLs for the rest of the world all incorporated dual row timing chains. There was cost and engineering to source not only a special chain but also single row sprockets, documentation, and inventory the special (shitty) parts.
Perhaps the expectation was that the relatively low duty cycle expected from the US market could allow a reasonable cost savings in the cam drive over many thousands of engines. My experience in the industrial diesel business is that the cost to introduce a new part and maintain it was generally more than offset by the cost savings if the volume was high enough. It seems that their calculations for life expectancy were off, however (we had similar experiences with our engines!)
 

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1983 380 SL
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Thanks for your 380SL:s life story Jyuma, very interesting.

With the risk of being thrown out of this wonderful forum by posting the same text twice I'm taking the chance anyway since otherwise the text below could be taken as answered as it drowned in the rest of my text when posted above.

Does the chain wear in a linear proportion to the cam sprockets? If so would it make sense to change them as well while I'm at it, thinking that the worn sprockets might speed up the wear of the new chain?
I assume there's at least one gear further down along the chain, also there are some plastic sliding rails further down which of course require even more work to get at. Has anybody changed at least the sliding rails and/or the gear down there or are they not so critical?
There are 3 gears down below that you can't see unless you pull the front cover. I wouldn't worry about them too much unless a problem developed with one or all of them that was far more serious than the possibility of a little wear.

Changing the lower guides is generally considered a luxury most don't have. Unless there is a compelling reason to pull the engine I wouldn't bother with the lower guides. They are not known to cause catastrophic failure.

Replacing the cam sprockets is a matter of some speculation... yes they can wear but how much it effects chain life appears to be a matter of opinion. I would ask if there was a compelling reason not to change them... availability and cost come to mind... but why not change them while you already have easy access to do so.

There are excellent pictures of the entire chain route someplace on the forum, with views of not only the chain but all the guides and gears as well. I don't remember what thread they are in but I'm certain others will.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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There are 3 gears down below that you can't see unless you pull the front cover. I wouldn't worry about them too much unless a problem developed with one or all of them that was far more serious than the possibility of a little wear.
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Replacing the cam sprockets is a matter of some speculation... yes they can wear but how much it effects chain life appears to be a matter of opinion.
It is an interesting question. Why do we focus on the cam sprockets when there are several others that could be equally or more worn? Wouldn't the smaller diameter crankshaft sprocket likely be more worn than the cam sprockets. And if we put a new chain on a mix of new and old sprockets, does that make sense? No doubt changing all the sprockets would be best (but not easy!) But is changing only two and not the others better than not changing any?

It would be interesting to see a comparison of sprocket wear on engines that have had the front cover removed.

On my car, I figured the cam sprocket teeth looked OK, but I had no way of judging that really. Somewhere on this forum, there is (or was) a post that showed affect of wear on
tooth profiles. I may try and find it.

This is not it, but does have an explanation of chain wear. He also says that sprockets are made from harder steel and should last twice as long as a chain. Scared of changing camshaft sprockets

This is the one that I recalled that shows tooth shape when worn (cant say I fully understand the jpg): Timing Chain Slack and Cam Gear Replacement Question

 

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If the chain is significantly stretched due to wear (as gauged by really late cam timing marks) the sprockets are probably going to be worn as well. In principle with chain drives in general all of the sprockets should be replaced with the chain to restore the original life expectancy. I wonder if the crank sprocket is visible enough for inspection through the hole in the front cover if the front seal is removed? Wear in the other two sprockets would not affect cam timing but they would accellerate wear in the new chain.
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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Discussion Starter #246
...
Replacing the cam sprockets is a matter of some speculation... yes they can wear but how much it effects chain life appears to be a matter of opinion. I would ask if there was a compelling reason not to change them... availability and cost come to mind... but why not change them while you already have easy access to do so.
...
Sometime this year I am going to pull the valve covers off my 190K mile 560SL.
I purchased her at 184K miles and have not yet done an inspection.
If the Cam Sprockets and Timing Chain show little or no wear and the Timing Marks line up, I'm really considering only replacing the plastic Guides. My thinking is if something is working properly, why introduce a new part that might have a manufacturing defect? Those plastic pieces do deterioriate over time and I can see that they are #1 priority to replace. Also, I think a regularly driven R107 with regular Oil Changes ought to have little wear.
 

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1983 380 SL
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Sometime this year I am going to pull the valve covers off my 190K mile 560SL.
I purchased her at 184K miles and have not yet done an inspection.
If the Cam Sprockets and Timing Chain show little or no wear and the Timing Marks line up, I'm really considering only replacing the plastic Guides. My thinking is if something is working properly, why introduce a new part that might have a manufacturing defect? Those plastic pieces do deterioriate over time and I can see that they are #1 priority to replace. Also, I think a regularly driven R107 with regular Oil Changes ought to have little wear.
You are a wise man Carl. From my many years involved in aviation I've known many A&P mechanics who say exactly what you just said. Don't go replacing parts for the sake of replacing parts just because you assume the new part is better than the old part. The old part is a proven performer, the new part is an unknown.
 

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When I changed my timing chain I noted that cam sprocket wear was primarily in keyway area. The sprockets themselves had little wear. The keyways were wallowed out bad enough to cause several degrees of what appeared to be stretch. New sprockets fixed it.
 

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You are a wise man Carl. From my many years involved in aviation I've known many A&P mechanics who say exactly what you just said. Don't go replacing parts for the sake of replacing parts just because you assume the new part is better than the old part. The old part is a proven performer, the new part is an unknown.
As someone who has spent 30+ years in aviation, I would also point out that we change many parts based on time standards, regardless of whether or not they are working, because you don't want a failure at a critical time. Depending on the part, it may be wise to change it even if it's working. Water pump? If it's working, don't bother. Timing chain with 100k on it? Not hard to change and worth the piece of mind.
 

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1983 380 SL
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As someone who has spent 30+ years in aviation, I would also point out that we change many parts based on time standards, regardless of whether or not they are working, because you don't want a failure at a critical time. Depending on the part, it may be wise to change it even if it's working. Water pump? If it's working, don't bother. Timing chain with 100k on it? Not hard to change and worth the piece of mind.
You are 100% correct... my original comment to Carl had references to scheduled maintenance in aircraft engines and parts reaching their end-of-service life, I took it all out in favor of brevity. (y)

I read an article in Sport Aviation a few months back about the dangers of doing too much maintenance. It was very enlightening about introducing problems that didn't exist before you fixed them. :)
 

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You are 100% correct... my original comment to Carl had references to scheduled maintenance in aircraft engines and parts reaching their end-of-service life, I took it all out in favor of brevity. (y)

I read an article in Sport Aviation a few months back about the dangers of doing too much maintenance. It was very enlightening about introducing problems that didn't exist before you fixed them. :)
We call that the dreaded "recreational maintenance".
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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Discussion Starter #252
You are 100% correct... my original comment to Carl had references to scheduled maintenance in aircraft engines and parts reaching their end-of-service life, I took it all out in favor of brevity. (y)

I read an article in Sport Aviation a few months back about the dangers of doing too much maintenance. It was very enlightening about introducing problems that didn't exist before you fixed them. :)
I have concerns about newly manufactured parts.
In the Electronics Industry we have a term "infant mortality" meaning if an electronic part is going to fail, its going to fail a short time after its installed. After the "infant mortality" period its very unlikely its ever going to fail.

Probably the most fail proof new part is one removed from YOUR car after that infant mortality period and installed on my car :) Then there is the competence level of the installer. How many times have you taken something apart and ended up with a few extra screws? Or unknowingly ruined or degraded a part in the process, forgot to torque that bolt to spec, or caused that bolt or thread to loose its strength later causing a failure?
 

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Probably the most fail proof new part is one removed from YOUR car after that infant mortality period and installed on my car :) Then there is the competence level of the installer. How many times have you taken something apart and ended up with a few extra screws? Or unknowingly ruined or degraded a part in the process, forgot to torque that bolt to spec, or caused that bolt or thread to loose its strength later causing a failure?
Carl; I add one more to this list. How many times have you taken something apart with the confidence of knowing you have brand new replacement parts ready and waiting; only to find the new replacement parts do not fit? For this reason I don't trash the old stuff until I know for sure the infant mortality period has passed. About 1/4 of my shelf space is devoted to the old parts graveyard. An important corollary is whenever I finally clear a graveyard shelf I discover I needed that stuff shortly after disposal.
 

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Carl; I add one more to this list. How many times have you taken something apart with the confidence of knowing you have brand new replacement parts ready and waiting; only to find the new replacement parts do not fit? For this reason I don't trash the old stuff until I know for sure the infant mortality period has passed. About 1/4 of my shelf space is devoted to the old parts graveyard. An important corollary is whenever I finally clear a graveyard shelf I discover I needed that stuff shortly after disposal.
Funny but I have the same strategy.

I removed the old chainstretcher and i can push it in by hand until about 1/2 inch without problems so I'm thinking if this could have something to do with the timing mark being of on the passenger side considering the engine has only been running for 80.000km ie around 50.000 miles.
Well I'll put the new one in including the rail and the slide rail and we'll see how it lines up before i change the chain. This is the good thing about being your own mechanic in your own garage, you can test things without having to hurry.

Once again thanks for a great forum and all the answers, must say that this really got the comments going in this thread after being in some sleepy trance for a while.
 

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Funny but I have the same strategy.

I removed the old chainstretcher and i can push it in by hand until about 1/2 inch without problems so I'm thinking if this could have something to do with the timing mark being of on the passenger side considering the engine has only been running for 80.000km ie around 50.000 miles.
Well I'll put the new one in including the rail and the slide rail and we'll see how it lines up before i change the chain. This is the good thing about being your own mechanic in your own garage, you can test things without having to hurry.

Once again thanks for a great forum and all the answers, must say that this really got the comments going in this thread after being in some sleepy trance for a while.
I can't see how the chain tensioner could effect the cam timing marks. Chain stretch (wear) or the chain jumping a tooth or badly worn sprockets and/or Woodruff keys are the causes of cam timing mark alignment problems... not the tensioner. I'm not saying you shouldn't change the tensioner... only that it is not the cause of cam timing mark alignment problems.

One other thing can cause cam timing mark alignment problems... having the heads and block milled in order to restore flatness. Anything that changes the total distance between the crank sprocket and the two cam sprockets, in the counterclockwise direction, will result in the cam timing marks not aligning properly.
 

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1984 280sl 5spd, 02 E320 4matic, 79&79 450sl part-out, 78,79,81,83 300CD, 79 280CE
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Have not even taken car cover off of the 84 280SL, since parking it early Oct. Building a 78' X 46' building, and starting a salt water shrimp farm took all summer, and most of the fall. Hopefully I will have more time to work/play with the R107's this year. Yesterday bought this 1986???? M110 engine with 44000KM on it. Also got the clutch/flywheel. Running out of excuses not to get one of the 280SLC's running. One question is I thought that M110 production ended in 1985. This engine came out of a 1986 Gwagon. Owner swapped in an OM617 turbo diesel, keeping the 5 speed Getrag in the Gwagon. Paid $250 for it.
2621997
2621998
 

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1983 380 SL
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Have not even taken car cover off of the 84 280SL, since parking it early Oct. Building a 78' X 46' building, and starting a salt water shrimp farm took all summer, and most of the fall. Hopefully I will have more time to work/play with the R107's this year. Yesterday bought this 1986???? M110 engine with 44000KM on it. Also got the clutch/flywheel. Running out of excuses not to get one of the 280SLC's running. One question is I thought that M110 production ended in 1985. This engine came out of a 1986 Gwagon. Owner swapped in an OM617 turbo diesel, keeping the 5 speed Getrag in the Gwagon. Paid $250 for it. View attachment 2621997 View attachment 2621998
Nice catch... now get to work. And I remember when you starting building that salt water shrimp farm. How did it work out?
 

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Nice catch... now get to work. And I remember when you starting building that salt water shrimp farm. How did it work out?
Other than only getting to put only about 1000 miles on the 280SL, and working 12/14 hour days 7 days a week, everything has gone great. Really under estimated the craving of fresh sea food in Montana. Have been selling shrimp for 2 months now at 21/22 shrimp per pound, and already selling about 75% of my total production capability. Will not get to full production for about 3 more months. So, already looking at adding another 62' x 46' on to the building, and doubling my production next year. This year need to haul/level about 4.5 feet of fill dirt/gravel, get some payments made, and drive the R107 more. Have a trip planned to Kootenai Falls, just west of Libby this spring.
 

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I can't see how the chain tensioner could effect the cam timing marks. Chain stretch (wear) or the chain jumping a tooth or badly worn sprockets and/or Woodruff keys are the causes of cam timing mark alignment problems... not the tensioner. I'm not saying you shouldn't change the tensioner... only that it is not the cause of cam timing mark alignment problems.

One other thing can cause cam timing mark alignment problems... having the heads and block milled in order to restore flatness. Anything that changes the total distance between the crank sprocket and the two cam sprockets, in the counterclockwise direction, will result in the cam timing marks not aligning properly.
Thanks Jyuma, I was just hoping it could have something to do with it considering the timing chain wasn't fully stretched but i guess I was wrong. Well at least you saved me some unnecessary mounting to test my theory. I'll just change the chain.
 
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