Zero degrees timing chain stretch
 

Hi all,

My '87 300D with 279Kmi (94Kmi on the timing chain) has NO timing chain stretch :) The PO original chain was replaced as PM by the previous owner the week I bought the car. I've run synthetics the entire time mostly Delvac 1 or Mobil 1 with oil changes between 6500-9500 miles and the engine runs very strong. On other sites its been suggested that the use of synthetic oil seems to eliminate timing chain stretch and frequent oil changes with good mineral oil can come close to the same.

Regards,

That's exactly right. I ran my original 240D engine 380,000 miles with religious 3,000 mile oil change interval using Delo 400. Synthetic should allow you to extend the intervasl some as long as the engine is not otherwise worn allowing excessive fuel or combustion by-products into the oil.

Have a great day,

Larry, are you saying you ran 380K miles on the same chain? If so that's quite amazing.

My car has 200K+ miles and a mechanic told me last year the chain is not stretched. He didn't say 0 degrees, but only that it is not stretched. I think I believe him.

Larry,

I was hoping you'd chime in :) What happened at 380,000 miles? Are you on the original chain or how much was it stretched when it was changed?

The point here is that adhering to a change interval that's best for your engine can save maintenance in the long run - like changing the timing chain. For MY driving habits and engine, changing synthetic oil every 6500-9500 miles works. I've tested it with oil analysis and engine condition confirms it. For others, mineral oil changes will work better. In my opinion, changing oil at the "right time" - either synthetic or mineral - is very important. More important than what kind of oil you use.

Regards,

DieselAddict,

Has your mechanic ever measured the chain stretch? Either with a dial indicator or lining up the marks on the cam and tower? Some mechanics will say that chains don't stretch or that it doesn't matter - that's completely false!

My '87 300D spare engine has 3-4 degrees at 175Kmi and I've heard of some 617 engines with as much as 17 degrees of stretch!! The chains DO stretch if the engine has not been well cared for (changing the oil).

Regards,

My 603 had 13 degrees at 270,000 miles. Needless to say it got replaced along with the tensioner.

The 380,000 mile mark on the old 240D was a long time ago. I had checked the chain not too long before the engine came apart and the marks still perfectly aligned. I did not use a dial indicator. Once the marks no longer align, that is the time to get more precise with the dial indicator.

The rear seal failed just all of a sudden. I was screaming along in the heat of the summer on an Interstate. I rolled in to get fuel, swung around to turn the car around in a truck stop. I immediately got out and noticed a trail of oil where I had just turned around. I opened the hood and could see a puddle of oil probably 3 inches in diameter. The car could not have been setting there 60 seconds at that point.

Before this stop, it had NEVER leaked a drop of oil anywhere. I got a gallon of Delo at that truck stop and went on the rest of the trip which was probably about 500 miles before I made it back home. I used up the gallon of oil to make that 500 miles.

The engine had developed a noise that I thought was strange. When the motor came apart, it had a failed ring land on one of the pistons that would have given some catastrophic problems at one point had it not come apart. Also it was discovered that (big suprise) the rope seal was no longer touching the crankshaft.

This was the original chain.

The cause of chain "stretch" is particulate matter from less than frequent oil changes. This particulate matter over time wears the rollers and pins. Think about it, if each roller/pin were to wear one ten thousandth of an inch, you are talking several thousandths of overall chain "stretch."

Changing a chain for preventive maintenance reasons does not in itself prevent chain failure. These chains typically don't fail, a rail breaks or something else that CAUSES the chain to break. If the chain is stretched then, of course, you need to offset a sprocket or replace the chain in order to have proper timing.

Closely inspect the chain rails, tensioner and all associated timing chain components when checking the chain.

Have a great day,
Change oil hot and change oil often!

How close did you come to hitting TDC at the crank and cam with the new chain?

In my SDL, I can't do better than 4 crank degrees either way with a new head and new chain. I don't know if the marker is properly aligned since I don't have a dial gauge. I tried 4-BTDC and now and 4-ATDC. Can't tell the difference.

Thanks,
Sixto
91 300SE
87 300SDL
83 300SD

Is it possible to measure a chains length after it has been pulled from an engine to see if its worn?
For OM617 chain with 280,000miles. My mechanic replaced it but didn't measure the stretch in the right way so I have no Idea if it was really worn. The car has always had oil changes done in a timely manner.

md21722, I assume my mechanic measured the chain stretch one way or another as I specifically asked him to inspect it while he had the cover off to do valve adjustment. I don't think he dismissed chain stretch as a possibility. Besides he listed a bunch of other things on my car that he recommended replacing so I believe if he lied to me it was about what needed to be done, not what didn't need to be done.

We didn't check it again after the new chain went in, I couldn't tell you, sixto.

"Is it possible to measure a chains length after it has been pulled from an engine to see if its worn?"

I was wondering that same thing. It seems to me I saw someplace where a chain was held "sideways" and the arc measured to determine wear. I bought a 616 engine off eBay and the chain shows very little stretch via timing & cam marks but I would like to check it out better.
I will post this question later on into the project if no one reading this thread knows.

All this discussion of chain stretching confuses me. If the links on the sides don't actually get longer, I fail to see how the chain gets longer. If the rollers and pins wear the space between them changes, but this is not cumulative. The center of each pin stays in the same relative location that it was when the chain was new. And how does oil changing affect the stretching of the links?

If the chain fit the to sprocket gets sloppy, and the sprocket is wearing and getting smaller in diameter where the chain engages the teeth, then I think I can understand how the chain would seem to have gained and "apparent" length. Otherwise I am not able to see how the chain gets longer. Jim

Dirty oil wears the chain faster. The parts that hold the chain together get looser and "become stretched" because they don't fit as tight together anymore.

Jim Smith,

Wear of the pins and holes is certainly cumuilative although chain stretch is a bad description, better is chain elongation.

If each pin and each pin hole were to wear .001 inch where they touch each other, chain each link would be offset by .002 inch from new. Thus the overall measured length will be the original chain length plus .002 inch times the number of links.

If you compared a new chain to a worn one, you would see a definite difference in length. Also the arc of a worn chain would be greater due to the "slop" between the pins and holes.

P E H