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  #1  
Old 01-22-2009, 02:39 PM
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Timing chain, replace it at 5* stretch now?

Or not? How much stretch is acceptable and if you had the valve cover off on your 1983 300 TDT and a new chain ready to go, would you replace it now or is 5 degrees of stretch no real big deal?

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  #2  
Old 01-22-2009, 02:49 PM
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I would and eliminate worry.
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Old 01-22-2009, 02:49 PM
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How are you measuring it?
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Old 01-22-2009, 02:51 PM
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Originally Posted by oldsinner111 View Post
I would and eliminate worry.
That's kinda where I've been leaning! I had the head at a machine shop less than 1000 miles ago and didn't bother to replace the chain then because it looked OK to just drive carefully around town close to home to let everything "settle in."
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Old 01-22-2009, 02:54 PM
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Originally Posted by winmutt View Post
How are you measuring it?
I'm looking at the timing mark on the Camshaft and lining it up with the matchmark on the cam tower while rotating the engine in the normal direction of rotation by turning it at the crank pully. When the Camshaft mark lines up at the cam tower, the harmonic balancer marks are 5* degress late, maybe a slight bit less.
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Old 01-22-2009, 02:54 PM
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I'd worry more about the guides, rails & tensioner than I would about the chain.
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  #7  
Old 01-22-2009, 02:57 PM
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I did replace the tensioner spring and the slipper foot when I had the head off. The upper guide rails have been replaced as well.
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  #8  
Old 01-22-2009, 03:45 PM
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Have you got an offset key in the cam sprocket or the "normal" one. I have a 2.5 degree offset key here which would fix your problem if you want it...
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Old 01-22-2009, 05:17 PM
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5 degrees is not bad, any more and it becomes questionable. The general rule of thumb is replace the chain every 100,000 miles. I know there will be some that will disagree. It's not hard to do, and with the right crimping tool, can be done in a couple of hours. The last one I did was on the 300D, it had several degrees of stretch, a new chain made a world of difference. The worst one I saw had 12 degrees of stretch, surprised it even ran.

There are some users who will rent the correct crimping tool for a small fee and deposit. Check the tool rental forum. Others have used vise grips, it's a real pain in the ass to do, but can be done.

If you do decide to replace the chain, use a press on master link. Although it makes the job easier, I have not seen an "easy clip" link in years, they were discontinued from MB in the late '90's.
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Last edited by AMH; 01-22-2009 at 05:37 PM.
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  #10  
Old 01-22-2009, 05:33 PM
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Quote:
Originally Posted by MBNRA View Post
I'm looking at the timing mark on the Camshaft and lining it up with the matchmark on the cam tower while rotating the engine in the normal direction of rotation by turning it at the crank pully. When the Camshaft mark lines up at the cam tower, the harmonic balancer marks are 5* degress late, maybe a slight bit less.
First this not an indication of stretch, this is cam timing. There is like a 4* or more error margin the way you have measured it. Measure it with 2mm lift method. There is no need to replace the chain, bad crimps (common enough) lead to short lifespans. They make offset keys for this purpose and there is no need to crack the chain. There is no specified replacement interval in the FSM, I think they expect the chain to last all the way to the last offset key. Not that I would go that far but I believe 6* is the first offset, you are in spec but if you have the time its probably worth it.
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  #11  
Old 01-22-2009, 05:34 PM
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timing chain

Roll a new chain in, it,s that simple.
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  #12  
Old 01-22-2009, 05:46 PM
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Quote:
Originally Posted by pop & blow View Post
Roll a new chain in, it,s that simple.
Why risk a bad crimp with a known good chain? Why spend hundreds of dollars when it should only cost a few?
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  #13  
Old 01-22-2009, 07:16 PM
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Quote:
Originally Posted by AMH View Post
5 degrees is not bad, any more and it becomes questionable. The general rule of thumb is replace the chain every 100,000 miles. I know there will be some that will disagree. It's not hard to do, and with the right crimping tool, can be done in a couple of hours. The last one I did was on the 300D, it had several degrees of stretch, a new chain made a world of difference. The worst one I saw had 12 degrees of stretch, surprised it even ran.

There are some users who will rent the correct crimping tool for a small fee and deposit. Check the tool rental forum. Others have used vise grips, it's a real pain in the ass to do, but can be done.

If you do decide to replace the chain, use a press on master link. Although it makes the job easier, I have not seen an "easy clip" link in years, they were discontinued from MB in the late '90's.
That is interseting as my timing chain shows 2 degrees of stretch (via the Cam Bearing Tower and alignment marks) with just over 200,000 on the odometer.
I do not know if the chain was previously replaced or there is an offset key installed (never worked up enough intrest to check the key yet).
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  #14  
Old 01-22-2009, 07:20 PM
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Quote:
Originally Posted by AMH View Post
The general rule of thumb is replace the chain every 100,000 miles.
This is a factually incorrect statement.
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  #15  
Old 01-22-2009, 07:23 PM
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The reading you got with the Camshaft Bearing Tower alignment method is a good indication you should check further and use the 2mm method to do so. This would also give you the spec you need to pick an offset key; if you want to use on.

To answer the question I think I would replace the Chain if it goes up to 6 degrees stretch as measured by the 2mm method.
If not replacing the Chain I would insert an offset key to return the Camshaft Timing to normal and re-time the IP.

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