timing chain rails - is it enough?

[rsmcmahon]

I’m getting ready to schedule a service appointment for my 92 400SE (V8 Engine 119.971) to have the valve cover gaskets replaced because both the right and left gaskets are leaking oil next to the distributor caps.

Since my car has 103,000 miles I was wondering if it would be advantageous, since the valve covers will be off, to also have the UPPER TIMING CHAIN GUIDE RAILS (left and right) replaced. I’ve done several searches concerning timing chain maintenance at 100k miles and it seems there are VARIOU opinions concerning timing chain replacement.

Since I don’t have a problem and I only want to perform preventative maintenance, what would you suggest? Maybe just replace the upper timing chain guides and the chain tensioner? I want to remain cautious, but I don’t want to spend thousands to replace the chain and etc...

Thanks for anyone’s recommendations or suggestions!

Russell

[seacoast_benz]

I believe you should be guided in your decision by a chain stretch measurement. If it's still close to within spec, you might decide to revisit the chain at 125K.

The rails, yeah, absolutely do the rails. Too many horror stories about brittle old rails getting fractured and pieces being processed through all of the valvetrain on that bank. Yikes!

I think the rule is that chains rarely fail without giving some warning first, like slap on startup. Rails can and do fail without any symptom.

s/b

[SCOTTFISH]

I have a 90 420sel with 110k. I am having the timing chain service as we speak. The MB mechanic is replacing the guide rails, tensioner, and checking the chain for stretch. He did not mention anything about the lower rails. Should I be concerned that he has not mentioned it? Should they always be replace along with the upper ones or is it sort of like brakes where you will replace 2 sets of fronts for every 1 set of rears, as so to speak? I would think being a MB mechanic he would have checked the lower rails. Do the lower ones generally last longer since more chance of oil being there than the top ones? Any advice I would appreciate.

Also, as we speak, I'm having the chain replaced on my '69 230/8; and my mech says the rails are fine. The old ones held up a lot more. And it's a single chain. But have the chain replaced. And my valve seals are OK, too. I'm suprised.

[Rockman59]

He did not mention anything about the lower rails
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Seems to me that I remember reading on this forum that the lower rails normally need not be replaced, at least not at the mileage that the uppers are usually done. I had the chain/railings, etc, done on my 560 SEL wtih 110K miles about a year ago and my trusted mechanic did not do the lower rails. And I know he would have done the lower rails if he felt it was necessary.