timing chain replacement schedule

[Benz300]

Given the w124 has a timing chain and not a belt, when does the scheduled replacement ask for it to be done ? 150K ? 100K ?
I"ve read threads that deal with the consequences of it breaking but if that's the case why doesnt the dealer recommend a specific mileage when they should be scheduled to change and why doesnt the manual reflect it's change unlike regular timing belts' intervals ?
thanks.

[Duke2.6]

The timing chain is not a "maintenance" item. There is no recommended replacement interval. The chain and tensioner should be checked anytime the head is removed.

Poor oil change discipline typically shortens timing chain life due to wear, but if the oil is changed IAW the manufacturer's recommended intervals, the chain should last at least until the head needs to be rebuilt.

Duke

[Mike Murrell]

Here's my take on this issue.

If I'm not mistaken, you have the M103 motor. These engines have "short" timing chains. I recall reading post(s) here by techs who have indicated the timing chain issue isn't as big a problem for M103 motors as it is on the 420's that have "longer" chains. Even then, it may be more of a guide rail issue than chain. Don't know for sure as I do not own a 420.

I put over 300K on an asian 4 cyl engine. Never changed the timing chain. As Duke 2.6 mentioned, alot depends on oil change intervals and also, how sanely you drive the car.

Mike is right, these engines have a short, simple chain, but there is an additional reason that this engine has very long chain life. These engines have a ratcheting tensioner. As the chain wears, the tensioner takes up the slack and KEEPS the chain tight even during cold starts before the oil pressure builds up.

Many chain failures are on the engines that don't have a ratcheting tensioner. This adds stresses to the guides and associated parts while waiting on the oil pressure to come up. The oil pressure is what causes the tensioner to put pressure on the chain to take up the slack.

Good luck,

[Benz300]

thanks everyone for the replies. Now, is it only the M103 engines that have these self adjusting ratcheting tensioner. what about the M104 engine ? I ask because my friends owns a 92400E with around 70K miles and I'd like to inform him of any upcoming maintenance issues that would come his way.
thanks again.

All of the engines from the mid eighties on have ratcheting tensioners, but that's not the only reason that your 103 engine is pretty trouble free in the timing chain area. As was said earlier the 103 has a short chain and is a single cam engine. That in addition to the ratcheting tensioner allows you to just keep your oil changed and not worry about it.

The 104 engine has a ratcheting tensioner, but it is a two cam engine so there are more gears and MANY more chain guides to give trouble.

The 400E your friend has does not have a 104 engine, it has a V8. The V8's need particular attention paid to their chains and associated parts. The V8 chain is at least twice as long as the 103 chain and has a zillion guides and gears. These guides are plastic and will get brittle with age and mileage. If one breaks it will typically jam in the chain, breaking the chain.

The key is not simply periodically replacing the chain. The chain would probably never break on its own. The key is inspecting periodically to see that the guides and everything are in good shape. Since everything comes apart to do this, a new chain is usually rolled in at the same time.

Hope this helps,

[Gilly]

As the chain wears, the tensioner takes up the slack and KEEPS the chain tight even during cold starts before the oil pressure builds up.

Larry:
The spring inside the tensioner keeps tension on the chain during startup.
If the spring fails the ratchet mechanism is there in hopes that the chain will still remain tight enough before oil pressure builds up.
In the event of loss of oil pressure, you have both the ratchet and the spring to help maintain chain tension before the owner has a chance to shut down the engine.

Gilly

Gilly,

Isn't that sort of the same thing I said? I described it by indicating the tensioner would retain tension BEFORE oil pressure builds up and you indicate that it will retain tension AFTER oil pressure is lost.

I'm not trying to duel here or anything, I just wanted to make sure that I was correct.

Have a great day,

[Gilly]

Mmmmm, not really, you never mentioned the spring. To me, between the spring and the oil pressure, it would be fine without the ratcheting feature. The ratcheting feature, IMHO is only useful in the event of both a loss of oil pressure AND failure of the spring, kind of an "emergency fall-back" position. With the spring in place, the ratcheting feature is a little German over-engineering. BUT it's nice to know it's there.

Gilly