w202 timing chain - do I really have to change it?
 

I've seen TC's blow on VW VR6's as their tensioner design are a weak point along with early Jag V8's.Haven't heard about one going in a well taken care of W202.

111 is dohc

I'm not a mechanic, but I've never heard of a timing chain requiring replacement on an M111 engine.

ok thanks guys. It's DOHC? That's cool too.

All M111 engines are DOHC 16V four bangers with a large dual-row timing chain that is VERY robust, BUT like all things, will wear out. What influences the life of your chain? OIL CHANGE HISTORY. The chain is bathed in engine oil, and a poor history of oil changes means dramatically shortened chain life.

My dealer freaks out and says all M111's chould have a new chain/tensioner by 160,000kms (100K-miles) but I call BS on that. My indie mechanic has never seen an M111 chain worn at that mark, even with uneven oil changes. However, he usually starts checking them for stretch at 200K (125M) and finds that by 250-300K (150-190M) that he changes them out for peace of mind. However, he has had new customers come in with engines at over 350K and the chain was original and while worn, not in bad shape.

A new chain/tensioner runs about $500 P/L, and compare that to the cost of a new head or a buch of bent valves. Cheap insurance. I'll probably have mine done at the 250K or so mark (about 150K-miles).

A long time ago when the M111 was new, one of the local dealers had a Mercedes rep with an opened unit, showing off the new engine. It was one of the reasons I didn't hesitate to buy an M111 equipped car. Massive crank bearings, overbuilt block, big dual-row chain, and so on. Overengineered like it's M104 cousin, and laks the head gsket problem of the six-pot engine. Like some other MB engines, an M111 will never wear out its bottom-end if you change the oil/filter on a regular basis. Every other part of the car will wear out first...

I don't know what to do about this one. I'm at 144k miles, and while I am unsure of the initial-owner maintenence (was a Starmark car, 1 PO) I have run Mobil 1 of 15w50 and now 5w40 (dealer) changed every 5k since 60k miles. The only thing I'm concerned about that could affect it's life is hard driving. My car gets vigorous exercise on the highway. I'm a bit trigger-happy when passing, etc, so it sees 5-3 kickdowns and redline probably 2-3 times a day. I wonder how negatively that would impact its lifespan.

Have your mechanic check the chain for stretch. Easy job, and you'll have a good idea of how worn it is. Personally, if I were you, I'd probably plan on changing it in the next year or so, just for insurance against a possible expensive repair. I'm betting, given the oil change history since 100K-kms, that the chain is in good shape.

I had to replace the valve cover gasket on my engine at 190K, and my tech checked the chain then, and found no wear, but I'll change it out at 250K regardless. Then I know the tensioner is new too.

(I have run Mobil 1 of 15w50 and now 5w40 (dealer) changed every 5k since 60k miles)

IMO, if you change oil every 5K then you don't need to use Mobil 1 , especially with MB engine where oil reservoir is 7.5 qts. I've used Mobil 1 because I am too lazy to get under my car so I've changed oil every 10K... for several yrs now, and no problem at all . Save your money

^ not a surprise. BMW has oil change interval set to 15000km and they have no issue with that whatsoever.

Run 200k-250k miles on it then yank the valve cover and inspect the guides and check for stretch. MB's inline engines can go almost forever without touching the chain. I have only heard of a small handfull breaking but those seem to be mostly fluke's.

Does not apply to the single row chain on the M103 engine. Despite their short path and no direction changes, the single row chain wears faster than the double-row chains of the later DOHC engines.

MY two cents is that you never know when it will break,you can check the back lash to see how much ware it has but that only tells you change it now,if you let it go you are sitting on a time bomb, MB. is looking out for there rep. by giving you a change time.Our 420 has 160 + and the original chain,but I dont jump on the gas for any reason,I hope mine will last a long time yet BUT I chose to take that chance.JNT

I'll assume the 420 in question is the M116 4.2L V-8. The timing chains and guides in those engines are ticking time bombs. Nothing in common with M111 four cylinder.