Slack in Timing Chain

[tuultyme]

I am moving this question to a new thread.  I noticed slack in my timing chain near the chain guide.  I do not know if this is normal or not. See pictures.  The engine was overhauled in 1987 and a new timing chain in 1991; currently there are 103,000 miles on the car.  I was trying to fix an oil leak; see other thread, I just wanted to know if there is supposed to be this much slack in the timing chain.  I ran the car last about 2 weeks ago.

Download Attachment: chain guide 1.jpg
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Download Attachment: chain guide 2.jpg
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Bruce; 268Blaugrun(green) 1970 280SL; IL

[Mark in KS]

Let me add this to the situation.  I rebuilt the top end of my 230SL this summer and came upon the other chain guide that's down by the distributor drive.  The facing on this guide was found in the bottom of the oil pan!  I was able to replace it, but a missing guide facing on that third guide could allow more slack like you have.

Good Luck!

Mark in KS

[ja17]

Hello Bruce,
Some slack is normal and the tensioner can handle it as the engine accumulates more mileage, up to a certain point. The basic rule of thumb is replace it every 100,000 miles if you are not sure of it.
Things like cutting (milling) the cylinder head and normal wear and tear increase slack in the chain. The tensioner will take it up until the tesnsioner reaches the end of its travel all the way in the up position.
The job of the tensioner is to keep the chain tight enough so it will not jump or jamb. It works on hydraulic pressure from oil but is not force fed. It retrieves engine oil which accumulates in a small pocket in the front of the head in the chain gallery. Chain movements move the tensioner sprocket pumping oil into the tensioner and hydralically pressurizing it taughnt. A spring in the tensioner aids the process but the hydraulic oil pressure does most of the work.
To check chain stretch, make sure the chain is tight and straight on the right side (opposite the tensioner side). Pump the tensioner sprocket, if it does not take up the slack, the chain may be at its upper limits and the chain may need repalcement.

These tensioners are very reliable and will usually last the life of the engine or several chains. Some owners will choose to replace it with every chain, although I have not seen one fail in my years of experience. This tensioner design was used on all overhead camshaft Mercedes engines until the introduction of the M110 double camshaft when a mechanical ratcheting with hydraulic type tensioner was introduced. Time has proven that this new design was not quite as durable as the previous!

Joe Alexander
Blacklick, Ohio