450SLC timing chain check

The Achilles heel of M116 and M117 engined cars is the timing chain.    As the engine is an overhead valve engine, the chain is used to make sure the valves open and close when they should.   On the V8 the chain needs to go to both heads and down to the crankshaft and so it is very long.    This exacerbates the potential problems compared to other engines.

Over time the plastic guides become brittle and the chain stretches.  The most likely failure is either due to a stretched chain or brittle guide, the guide breaks and causes the chain to jump a tooth.   Best case is valves and pistons meet, causing bent valves and the chain ripping a hole through the rocker cover.  Worst case is a completely ruined engine.

I’ve heard that the chain really should be changed every 100,000km.   My car has a full service history, but it doesn’t indicate if the chain was every changed.   I had this job done on both my 560SECs (also M117 engines).   Both cars were ticking time bombs – at around 300,000km they had original chains and cracked guides.

The only way to check is to remove the valve covers.  This is not a particularly difficult job on the M117:  It just involves removing the air cleaner assembly, spark plug leads and a few other pipes.   The picture below shows the chain and one of the plastic guides.   Straight away it is obvious this chain has been changed as the link is showing.   The original chains do not have the link.    The guides did not appear worn or discolored.

Timing Chain

I know a lot of work was done to the car about 12-18 months before I got the car – at about 230-240,000.   This would probably fit in with the condition of the chain, guides and sprockets.    In this case, the chain probably doesn’t need imminent replacement, although the correct procedure is to check chain stretch which I did not have time to do.    On various forums, I have read different things about the guides.   I have heard the Febi guides are not as good as the factory guides.   I have also read that there are uprated guides available.    I have not yet had a chance to investigate either option.


I had become increasingly concerned about the timing chain on my car.   I will need to do this job in future.   The good news is that it does not appear the engine is a ticking time bomb.

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