Now I know there are posts floating around here saying that a timing chain should be chained every so often and stuff and what could happen if it breaks.

But, what are the tell-tell signs of one that is overstretched or on the verge of breaking? As with most parts and engine mechanicals, there is usually a noise or performance difference before or when something is about to kick the bucket. I never came across a Mercedes where I could tell a guy that his timing chain is about to go, because I don't know what to look for or listen for. I usually see the car working fine, perfect, or after math when the car is dead. But, what are the signs before a timing chain goes? And would the average mechinic know this?

 

The only chain car that I am aware of that needs routine chain replacement is the Maserati powered Citroen SM every 30K at $1,500. Don't gulp, the A8 belt costs $2K which includes removal of the front clip.

Anyhoo, most chains can be expected to go well past 300K. Most American engines wear out well before the chain. I do hear that the old 420 does have some chain potential issues at 150K or so.

 

If it's your 560SEL (W126) you are asking about, change the timing chain and replace chain guides at 100,000 miles. Do not delay on this as your 560SEL engine will self-destruct if the chain slips or guides break. The guides get brittle with age and shatter, causing the chain to jump. To answer your question, a loose chain will "slap" the inside of the valve cover on start-up. If you hear this shut if off and do not restart... you have waited too long. This preventive maintenace is necessary on the 116 and 117 engines, as they are "interference" engines meaning the valves and pistons will collide if the chins slips even a little. Good luck with your W126!

 

I would expect a better design and product from MB. GM and Ford V8s don't have these issues.

 

Thanks for the info. Now I know what to tell people who ask these questions.

So far the 560 is still running fine and maintence here in Germany is way better for my pockets and the car than in the states.

GM and Ford V-8s of the 89-90 era I believed used a double timing chain. Which, by theory is stronger than a single but the double tends to stretch a little faster. Hm, but then again, I think MB solved that timing chain issue with it's more current products. But then again, who's to say, there is not many W220s with the mileage of the average W126 out there. Only time will tell. The timing chain issue seems to be pretty mum with the W140s and may not be too much of an issue in those cars. Maybe MB seen this and made corrections, maybe not. I might be all wrong.
And why did they do it like that in the first place? Or why did they use plastic guide rails? I don't have or really can think of a reason. I think the newer (S-Class) ones after the W126 use metal guide rails for the timing chain. Plus, the preventive maintenence is not much compared to the the $2,000 required for the Audi. The W126 t.chain work is about in the ballpark of $400 for the all required parts parts. (labor varies so it's a little hard getting a nice round figure for it.)

 

Thats y its good to have an uncle that can work on engine internals cause thats were my knowledge stops at least as far as doing the actual work.

 

Yes, BW the Chrysler 440 used a plastic sprocket too that by 100K wore down to nubs. Ironic that these two companies would hook up.

I never knew MB used plastic. I imagine they would claim that it made the engine quieter, same reason belts are used (the real reason is that they are cheaper and as long as they last beyond the warranty, why should the manufacturer care?) The Lincoln 4.6 with chains is as quiet as the Audi 4.2 with belts.

 

II Kings and Dave 420 responded to a 2006 post about the 560 SEL timing chains should be replaced at 100,000 miles, do you guys know anything about the 45o SL from the early seventies. I have a chance to buy a ;74 with 91,000 miles and am concerned about this perceived problem.