I'm assuming you want to manually rotate the crank, and see if the distributer lags or not.

But I want to make sure. Exactly how qould you diagnose a stretched timing chain in a 450SEL? . . . as opposed to a loose tensioner?

And how can you differentiate timing chain slack as being due to the tensioner or the chain itself?

If EITHER the chain or tensioner is bad, do we want to replace BOTH tensioner and chain, or just replace the part?

Thanks for any insights...

I don't know much about these things, but I'd personally recommend switching both the chain and the tensioner because after a while they may get worn and adjusted to each other, so if you only buy one or the other your engine may take it badly. Then again, I'm not a pro, but thats my $0.02.

Philly

I'm assuming the 4.5 is similiar to the 3.8 that I am newly familiar with. In a perfect world with no chain stretch when #1 is at top dead center the timing marks on each cam and the 0 on the crank timing marks will be lined up with their indexes.

However in the imperfect world of stretched timing chains things change. If you rotate the crankshaft with a socket (clockwise) until the right cam (passenger's side) mark lines up with its index mark you will find that the crank will not be at 0 degrees. If for example when the right cam is on its mark you find that the timing marks on the crank are 6 degrees away from zero the chain is said to have stretched 6 degrees.

I assume you could have a brand new chain and a bad tensioner. The chain would show no stretch but the weak tensioner would still allow the chain to slap on startup giving you the dreaded noisey chain everyone fears (for good reason).

Randy

Thomaspin has a website where he's posted a ton of great articles with pictures on changing timing chains, etc on his two Mercedes:

http://www.pindelski.com/

Click on cars, and in at least two of the articles he shows the degrees of timing chain stretch.


Also, Mike Tangas just checked the amount of stretch on his 72 280 SE 4.5 and ended up changing the chain and tensioner.

He posted the procedure and the results just this past week. Do a search under his username.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

What does a loose chain sound like on a cold start? On start up my 4.5 makes a loud scraping noise but I thought it might be the starter. The sound is brief and happens about one second after the engine fires.

That sounds like the classic "death rattle" of a bad tensioner. You are probably hearing the chain hit the cam cover before the tensioner fills with oil and tightens the chain. The chain may also be stretched.

Your engine is on borrowed time - you need to check this out!

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe