Timing chain, replace it at 5* stretch now? - PeachParts Mercedes-Benz Forum

winmutt · #1 01-22-2009, 01:49 PM

How are you measuring it?

MBNRA · #2 01-22-2009, 01:54 PM

Quote:

Originally Posted by winmutt

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.

winmutt · #3 01-22-2009, 04:33 PM

Quote:

Originally Posted by MBNRA

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.

pizzachef · #4 01-23-2009, 09:28 AM

Quote:

Originally Posted by winmutt

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.

Can you explain a little more how the cam tower mark method is not an indication of chain stretch? I mean, it SEEMS like it would be a quick way to check, albeit not very accurate, but I'm still pretty new to engine timing and whatnot.

dannym · #5 01-23-2009, 09:56 AM

The cam tower marks are used when first installing the cam to the engine, nothing more. It was never intended to be used to measure chain stretch.
Mercedes gave a precise way to measure it. That way is 2mm valve lift on intake #1.

That said. If you had 10* of stretch and it was running fine then your IP was timed to 10* stretch. With a new chain you now have to retime your IP.

Danny

dannym · #6 01-23-2009, 10:00 AM

Quote:

I do have the timing marks on the cam lined up and the marks on the crank at zero.

That makes no sense. This is what you should see:

For engines 617.950 (1980 and after), 617.951, 617.952; Camshaft code 05, specs are:
With new chain, 9 degrees ATDC.
With used chain (from approx. 20,000 Km), 11 degrees ATDC.

You really need to stop using the cam tower marks.

FYI
Mercedes Benz makes 4 woodruff keys for the correction of cam timing:

Part # 621 991 04 67, Offset 0.7 mm, For correction of about 4 degrees.
Part # 621 991 02 67, Offset 0.9 mm, For correction of about 6.5 degrees.
Part # 621 991 01 67, Offset 1.1 mm, For correction of about 8 degrees.
Part # 621 991 00 67, Offset 1.3 mm, For correction of about 10 degrees.

Danny