When is the right time to install a new timing chain? - Page 2 - PeachParts Mercedes-Benz Forum

babymog · #16 01-12-2011, 02:42 PM

Depends on whether you're using the word "stretch" in the literal sense, where the metal parts have been stressed beyond their yield point / plastic deformation limit (unlikely), or meaning that due to wear there is more slop in the pin/hole interface allowing the chain to be longer.

If a chain were to actually stretch the metal, you're on the edge of disaster, probably would shear the key at the cam gear or snap the camshaft before the chain will yield.

Agreed Roy, my reply is out of sequence.

charmalu · #17 01-12-2011, 02:50 PM

The Bicycle chain is subjected to grit, grime, water, and lack of luberication, so the wear is speeded up, compared to the MB chain that is is in a constant bath of "filtered" oil. (notice I didn`t say clean) so the wear on both chains is some what similar in that it is the pins and rollers that wear, that give the illusion of being streatched.

Charlie

leathermang · #18 01-12-2011, 03:02 PM

ON Hunter's post referenced above

Timing Chains Don't Last Forever

"Timing chain stretch does not exist = it is wear on the pins and bushings = Wear Elongation Measurement."

I have been trying to get people to use ' elongation ' instead of 'stretch' for years.. not making any progress either...

"Chain elongation/wear is not corrected by an offset Woodruff key.."

Technically correct... but moot if the Offset Woodfuff Key brings the situation back to where the IP can be set properly relative to the cams position.... and their position relative to the crank.

That is the value of the ' slack take up mechanism' ... the oil pressure operated ratcheting tensioner on the non load side of the chain travel.

So to the original question.. Technically you replace it when the offset keys are not able to bring it back into compliance with specs..
But the posts by Hunter reflect normal thinking on this subject I believe... wear does happen on the sprockets... so optimal situation is to renew them at the same time as the new chain. A worn sprocket will cause a new chain to wear much faster... and most of its wear happens in the first 20-30 K miles... assuming normal lubrication rules being followed.

#19 01-12-2011, 03:16 PM

You folks seem to be arguing over semantics, the chain does get longer as the individual contact points wear; call it whatever you like. Also the sprockets have corresponding wear and should be replaced at the same time.

One suggestion I thought was reasonable was to replace the chain/sprockets at about 250K miles, which is about half the expected life of the engine before a rebuild. This would result in the chain being replaced only once over the expected "life of the engine."

Jeremy5848 · #20 01-12-2011, 04:43 PM

This is a really interesting topic for me, what with my '96 E300D (W210, OM606NA) at 275,000 miles and AFAIK the valve cover has never been off to even look at the chain. I suppose I should at least check the camshaft mark against the crank's OT mark to see if there is an "elongation" or other signs of wear on the chain and sprockets. I'd hate to have the chain break and ruin this near-perfect engine.

Tanksowner · #21 01-12-2011, 05:01 PM

Quote:

Originally Posted by leathermang

ON Hunter's post referenced above

Timing Chains Don't Last Forever

"Timing chain stretch does not exist = it is wear on the pins and bushings = Wear Elongation Measurement."

I have been trying to get people to use ' elongation ' instead of 'stretch' for years.. not making any progress either...

"Chain elongation/wear is not corrected by an offset Woodruff key.."

Technically correct... but moot if the Offset Woodfuff Key brings the situation back to where the IP can be set properly relative to the cams position.... and their position relative to the crank.

That is the value of the ' slack take up mechanism' ... the oil pressure operated ratcheting tensioner on the non load side of the chain travel.

So to the original question.. Technically you replace it when the offset keys are not able to bring it back into compliance with specs..
But the posts by Hunter reflect normal thinking on this subject I believe... wear does happen on the sprockets... so optimal situation is to renew them at the same time as the new chain. A worn sprocket will cause a new chain to wear much faster... and most of its wear happens in the first 20-30 K miles... assuming normal lubrication rules being followed.

Forgive my seemingly naive response...how complicated of a job is it to replace the sprockets? I'm assuming it's an easier job when you have the chain out, but to have someone else do it must be expensive.

#22 01-12-2011, 05:06 PM

Quote:

Originally Posted by Tanksowner

Forgive my seemingly naive response...how complicated of a job is it to replace the sprockets? I'm assuming it's an easier job when you have the chain out, but to have someone else do it must be expensive.

I've never done it myself, I think the cost was in the Sub-$1000 range last time I had it done.

leathermang · #23 01-12-2011, 06:10 PM

Quote:

Originally Posted by Craig

You folks seem to be arguing over semantics, the chain does get longer as the individual contact points wear; call it whatever you like. Also the sprockets have corresponding wear and should be replaced at the same time.

One suggestion I thought was reasonable was to replace the chain/sprockets at about 250K miles, which is about half the expected life of the engine before a rebuild. This would result in the chain being replaced only once over the expected "life of the engine."

I agree with those thoughts too...
Hunter and I are not arguing ... we are using the correct terms which also match what the FSM uses...
However, in defense of semantics... and one of my heroes from about the six grade...

http://en.wikipedia.org/wiki/S._I._Hayakawa

Let me say that when dealing with machines as important to us as these are.. having people understand what others are saying and meaning IS IMPORTANT....

leathermang · #24 01-12-2011, 06:12 PM

Quote:

Originally Posted by Tanksowner

Forgive my seemingly naive response...how complicated of a job is it to replace the sprockets? I'm assuming it's an easier job when you have the chain out, but to have someone else do it must be expensive.

I have not done it... and the lower one may be a bear to get off....but you absolutely would want to make that decision while you had the chain out...
although I will say here that the instructions for changing chains is to link them together, KEEPING TENSION ON THE ONE GOING IN, so as to keep the relative position of those sprockets.....

Matt L · #25 01-12-2011, 06:19 PM

As a bicycle mechanic, we would also talk about "stretch" rather than "elongation" but only because it's easier to say the former. Perhaps some of the customers thought the metal really did deform, but nobody who works on the things is under that impression.

Motorcycle chains tend to have o-ring seals on the pivot pins to retain lubrication and keep the dirt out (although you can buy really cheap chains that lack these). Bicycle chains have no such protection. But motorcycle chains are much more expensive to replace than bicycle chains, especially the labor. And they are much more highly stressed; probably quite comparable to the demands put on a timing chain.

Meaning is important, but it appears to me that the phrase "chain stretch" has come to mean elongation rather than deformation. Words have meanings, but meanings change.

However, I don't go quite as far as this guy:

'When I use a word,' Humpty Dumpty said, in rather a scornful tone, 'it means just what I choose it to mean — neither more nor less.'

Jeremy5848 · #26 01-12-2011, 06:38 PM

Changing the camshaft sprocket is easy. Changing the lower sprocket requires pulling the timing cover, which is a lot more work. The vacuum pump, water pump, etc., all must come off, probably the radiator to make room. Then there's the crankshaft pulley/balancer and maybe the oil pan? Would need to check the FSM to be sure but definitely a medium to difficult DIY job. Rolling in a new chain would be simple in comparison. I will also make the statement (subject to correction from those with superior knowledge) that if the camshaft sprocket does not look worn, the lower sprocket is probably OK too. Finally, changing the timing chain before it's noticeably worn will help extend the life of the sprockets. "An ounce of prevention" and all that.

Jeremy

Tanksowner · #27 01-12-2011, 07:40 PM

Quote:

Originally Posted by MTUpower

I just did mine with the same mileage, plus the banana rail.

What is the banana rail? Am I going to be slapping myself in the forehead for not knowing what it is?

Matt L · #28 01-12-2011, 07:46 PM

Quote:

Originally Posted by Jeremy5848

Finally, changing the timing chain before it's noticeably worn will help extend the life of the sprockets. "An ounce of prevention" and all that.

That is also true for bicycles. Of course the cogs and chainwheels on a bicycle are very easy to change and not expensive (compared to yours), but it's still much cheaper in the end to replace the chain before it gets bad. The cogs will last for many years of daily use if you keep installing new chains.

If it's like a bicycle (and probably is), most of the wear will be on the crankshaft sprocket. Since there are fewer teeth across the bottom half, less chain elongation is needed before severe wear starts.

engatwork · #29 01-12-2011, 07:48 PM

On our '95 E300 I changed all the tensioners, slides and guides when I did the head gasket at ~260k miles. I did not change the chain at that time realizing that I'd be able to come back and roll a new one in eventually. I was going to try to get at least 300k out of it before installing a new one. The car has had a very aggressive service schedule.