I know that this is a well-worn topic around here, but my situation has a different twist. The mechanic that replaced the timing chain, tensioner, and gears in my car (74 450SLC, 100K mi.) replaced only the one (broken) chain rail, the inner left one, I believe.

Anyone seen enough of these to know if this now a time bomb waiting for one of the other rails to break?

hi

it would have been sooo easy to do it right then. common thought on replacing is 100k miles dependent on frequency of maintenance.

it would have been the right time to do all the available chain rails and brought the timing back original spec.

you'll get more answers i'm sure. but... i would have done it!

tks

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Thanks Much!
Craig

1972 350sl Red/Blk 117k
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1987 420sel gold/tan 128k
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Yeah, I probably won't feel at ease with this until I get into it myself and change the other rails, or if one of the veteran experts out here gives me some reassurance.

Might actually make a little sense that there is one of these rails in particular that causes most of the problems (left inner?)?!?!

No at all. The key factor with the chain rails is at least as much time as mileage; they're plastic and age slowly deteriorates them, making them brittle and increasing the risk of breakage. I seem to recall hearing the left inner guide is the most common offender, but it really doesn't matter. In your case, you'd have to assume the others are as old as the one that had already broken; they could well be the original parts. Remember that if MB recommended change at 100,000 miles, they hardly expected that to take 29 years to happen! My 560SL got new chain, tensioner, sprockets and guides this year at 148K purely for prevention, as I strongly suspected it had never been done. They found all the guides looking old enough to indeed be original--dark and brittle. One guide was half-broken and another snapped as they started to remove it--both being disasters ready to happen (and yes, I know and trust the shop).

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Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
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