Timing Chain Guides

Greetings,
I am new to this forum and have a question re: 79 450SLC

I read somewhere that there are plastic guides that are positioned against the timing chain inside the front of the engine and that these should be periodically replaced to avoid internal damage.
Is this a "do it yourself" type of operation or must it be performed by the dealer.
Would welcome any and all input on the degree of difficulty and any tips on this task.
Thank you in advance.
Kurt Bunting

[bobw]

The chain guide rails are made from thermoplastic and with the combined effects of oil, heat and time they become brittle. The timing chain also stretches as it wears giving rise to some slack which the chain tensioner cannot compensate for. What can happen then, usually on engine start-up, is that the slack chain flaps against a guide rail which snaps because it's brittle, the chain jumps a tooth or two on the sprocket and bang, the valves hit the pistons resulting in a big repair bill.

Thomaspin has produced a truly excellent photo documented procedure for changing timing chains and guide rails. Although it deals with the alloy block engines, the iron block versions are very similar. You should be able to find it through the search facility. Reading through it will help you decide whether it's a diy job for you.

--
bobw
1983 380SL
1991 BMW 735iSE

[DavidSoine]

The tough part of the job - to me, anyway, is stuck bolts on the accessory drive components/brackets. May not be such a big deal on the iron block, but it was a problem on the 560...

Anyone have good hints for removing stuck bolts? Esp. pro-active solutions (besides penetrating oil).

best,

Dave