Help, my head is exploding. Chain slap sound @ startup?

[ericgr]

After getting my 1984 380SL in perfect running condition in every respect (tons of power, ice smooth idle, just a pleasure to drive) I now have something that is worrying.

First the background, which is that about 2 years and 8000 miles ago the timing chain broke on the car and lots of work was done in the engine, all of it well as far as I've been able to see to date.

Recently the car was in front of a few mechanics and finally back to me where I fixed a number of mechanic mistakes myself and then fixed some other things. Anyway, the car runs beautifully.

One thing I do know is that a suspect mechanic did adjust the timing on the car amongst other things. The car has a new catalytic converter and pre-cats in there.

At any rate, now when the car sits for a few days and is started for the first time (thus cold), I hear a very brief sound from the front of the car that reminds me greatly of the chain slap that I heard before my car originally broke its timing chain. However, the sound is shorter than what I remember it doing before (you may hear it for maybe 1 or 2 seconds, before maybe 4 seconds). WHen it did it before, I thought it was perhaps something in the exhaust shaking. Now of course I'm not likely to accept that explanation anymore. If I turn-off the car after it makes the noise and turn it back on, you hear nothing and you will hear nothing again on the car turning it on or off or when driving. It seems to happen when the car has sat for a few days and is completely cold.

I suspect that the answer from the group is that I have to go in there, remove the valve covers, and look at the tensioners. Also, how would I check chain tension? I can go look in the manuals and will start there but if there are any rules-of-thumb/DIY tips I'd greatly appreciate them. Also if you have any other theories on the sound, I'm very interested. Any other explanations for the noise. Also, is there ANYTHING that a mechanic can do that is "dumb" that would damage a tensioner, stretch the chain, or break a tooth (would there be other symptoms of a broken tooth)? For example, adjusting the timing in some sloppy manner? And finally, there is some of that luby valve cleaner in the gas (it's like fuel injector cleaner). SOmetimes I wonder if, at a cold start, that stuff doesn't raise the octane so much that it causes the timing chain to flop a bit from all of that power at startup.