Life of Timing Chain - Diesel Engines - a poll
 

I have an 84 300 SD with 145K. The chain(s) appears to be in good shape, very little stretch.
I am curious as to how long these last. I have read all ranges and would just like to take an informal poll to substantiate an average lifespan.
Also does this item give any warning signs before going south??

The chain in my 240D (same chain as yours) was still in good shape at 380,000 miles. With frequent oil changes stretch will be minimal. Without adequate oil changes, the tiny particulate in the oil will wear the pins which in effect "stretches" the chain.

The chain itself will not fail unless an associated component breaks jamming up the works. The other cause of chain breakage is a worn tensioner.

Good luck,

251K.. And it worries me. Plan to check stretch whenever I get around to adjusting the valves. Have only had the car 4 months/20K miles. PO had it since 120K and was a good oil changer so hopefully it's in fine shape. Starts and runs fine in any temp, so it can't be that bad. I do plan to replace it, just because.

wolf,

Remember, stretched or not stretched, the timing chain should not worry you the most. It is the condition of the associated components that should get the most attention. This means the timing chain guides and the tensioner.

A stretched chain will make the engine run bad, but it will run. A failed tensioner or guide can cause major damage.

Have a great day,

Larry is absolutely correct. It would be interesting to find out just how many timing chains have failed on their own. Just offhand, I cannot think of any (I'm sure there must have been some) that weren't caused either by a failed tensioner or a driven component. I lost one due to a vacuum pump failure.

IMHO, more are changed because they had worn to the point that IP and valve timing suffered. Most of those were nowhere near the point of failure.

just my $.02,
Wes

I'd be inclined to agree if there anything like the chains on a domestic V8. In the not so great days of old, they got to using these worthless nylon gears with a couple of thin peices of steel on either side, and they would wear in a big way pretty quick.
I've seen those gears go more than a few times. Chains don't usually break, usually.

When I said it worried me, it was directed as much to the guides and such as the chain itself, but thanks for the warning anyway.

I've been intending to search and form a plan of attack, but glancing at the FSM kinda looked like you basical cannot replace all the guides without some pretty serious tearing down. That isnt a happy thought.. I could have been misled from the way it looked though.

I have good docs from new till 120K, and I have known the PO since he bought it at 120K and I know he's kept the oil changed, hopefully it'll stay in one piece awhile longer. It is on my to do list though..

To begin with, this timing chain system is NOTHING like a Domestic V8.

Secondly, you could get an idea about the condition of the chain guides by simply pulling off the valve cover and look at the top one that you can see. While the cover is off it wouldn't take too much more trouble to do a preliminary chain stretch check.

The accurate check involves a dial indicator and some very specific information and measurements. You can, however, get an idea of chain stretch by simply rotating the crankshaft clockwise, ALWAYS CLOCKWISE never backwards on these, until TDC is exactly at the pointer on the crankshaft damper. Look to see if the notch in the cam washer behind the cam gear is aligned with the notch on the cam tower. If you see it and it is perfectly aligned, you have virtually no stretch. If the cam mark is not in sight, simply rotate the crankshaft one full turn until TDC is aligned and then check the mark.

Good luck,

Larry,

Have you experienced a difference in reading between using a dial indicator and lining up the marks?

panda,

At 379Kmi my 2.5 Turbo has just under 3 degrees chain stretch, the engine idles between 2-2.5 bar hot oil, and starts instantly when 28F outside. It does however need a head gasket. I just got the car 3 weeks ago.

Good info Larry, thank you. I have not really done any hard core searching and reading about this chain/guide swap yet. I'm loosely hopeing to just wait till I'm swaping the motor into a nice, yet to be found, w126. I will check the stretch the next time I adjust the valves though, which will also be the first time I adjust the valves.(only had the car since thanksgiving)

Timing chain & tensioner
 

Hello, I'm brand new here (1st post) and a first time owner of a MB, which I love!

I read that the timing chain/tensioner should be changed every 100K miles. My '89 300E is approaching 198K and I'm the third owner. I have a few records from the PO but I do not think it has been changed in the past so I've ordered the parts for this to be done.

My question: Is this a complicated job (ie-pulling the engine) or something that can be done in a few hours by a mechanic?

Lining up the marks is NOT accurate. The marks are there close enough to get the chain and sprockets installed in their correct relationship.

I expect that the marks are probably within 2 to 3 degrees. To check, I align the crankshaft mark as perfectly as I can and see where the cam mark is. If it looks dead on, I consider it okay and not worth bothering with a dial indicator test. If the cam is lagging visually, it's time to get out the book and dial indicator.

A stretched chain is not an indication that it should be replaced. There are offset keys available for correcting the timing relationship.

Inspect the tensioner and chain guides. Those are your culprits. Rolling in a new chain while paying no attention to these other components is a total waste of time IMHO.

Hope this helps,

Larry,

So you do it visually more or less backwards than lining up the marks and taking a reading and if you don't like what you see you get out the dial indicator. How many times have you not liked what you see and found that the dial indicator was more accurate?

The reason I ask is that I know of many people who take readings by lining up the marks and the only time there's really a problem is when someone has moved the pointer.

It may be the same as those that think they can do wheel bearings without a dial indicator. The shop manual clearly specifies that bearing play is set with a dial indicator & I follow the procedure. However, I don't use one for "lining up the marks" and I think you do the opposite?

What exactly is the measurement measuring?
 

Okay! Time for some clarification. I've read its time to replace the timing chain if stretch is around 8 degrees. Is this 8 degrees of the crank, or 8 degrees of the cam? I would assume 8 degrees crank (4 degrees on the cam).

Tower

I just adjusted the valves on my latest catch 81 SD ,I alined the cam marks then checked the timing marks on crank and it looked to be about 6 degrees after TDC ,so this is not an accurate way to read strecth?

74 240 D
81 SD
81SD
86 Euro 500 SE
81 2WD Chevy Blazer 454 (for sale)

William Rogers.......

William,

The difference may be the series of engine. 60x people I talk to (that's all I've ever owned) don't see a problem and some have done it both ways with no diference. But its possible that on 61x engines its not accurate enough. It'd be nice to know for sure.