Timing Chain 2mm method - PeachParts Mercedes-Benz Forum

hawthorne90250 · #1 06-28-2006, 11:50 AM

I am in the process of checking my chain for stretch, when i use the marks on the camshaft and line them up my reading is 2 degrees BTDC, when i use the dial indicator 2mm Method (intake valve) i get 15 degrees ATDC which is about right per the MB Manual, My question is why such a differance between both?, I know lining up the marks on the camshaft is just for assy but should it not be closer?
Thanks

OMEGAMAN · #2 06-28-2006, 12:13 PM

Thats because the mark on the cam is for assembly. The 2mm valve lift is to accurately set cam timing not measure chain stretch.
The 2mm valve lift will work as a benchmark for further chain stretch but that is not it's purpose. Mercedes VW Porsche Audi and probably lot's more that I'm not familiar with have very precise methods of setting cam timing on both diesel and gasoline engines.
As long as the chain and sprockets are not worn out and the adjuster and guides are working proporly then you can go ahead and adjust cam timing and pump timing.
Remember the combustion chamber does not care how the fuel gets there. Or how the valve is opened, It could be by magic, as long as it happens at the right time. And in the case of our diesels it's a chain that drives a camshaft and a mechanical injector pump.

hawthorne90250 · #3 06-28-2006, 12:17 PM

Quote:

Originally Posted by OMEGAMAN

Thats because the mark on the cam is for assembly. The 2mm valve lift is to accurately set cam timing not measure chain stretch.
The 2mm valve lift will work as a benchmark for further chain stretch but that is not it's purpose. Mercedes VW Porsche Audi and probably lot's more that I'm not familiar with have very precise methods of setting cam timing on both diesel and gasoline engines.
As long as the chain and sprockets are not worn out and the adjuster and guides are working proporly then you can go ahead and adjust cam timing and pump timing.
Remember the combustion chamber does not care how the fuel gets there. Or how the valve is opened, It could be by magic, as long as it happens at the right time. And in the case of our diesels it's a chain that drives a camshaft and a mechanical injector pump.

Thanks for your reply, I tought the 2mm method was for measuring chain stretch? Also How do you adjust cam timing?.
Thanks

OMEGAMAN · #4 06-28-2006, 12:31 PM

You have to replace the key that drives the cam.
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1U50QNXGR1U50QO0QD&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1982&product=A4190-21382&application=000041392
here is a link to one of the key's available depending on how far off you are.
Check pump timing while you are there. Late pump timing can really kill performance and fuel economy. It's amazing how far off pump timing can be and the engine will run just fine.

hawthorne90250 · #5 06-28-2006, 12:40 PM

How do i know if the P.O has allready installed a off set key? is their anyway other than taking the cam gear off?.

OMEGAMAN · #6 06-28-2006, 01:36 PM

The only way I can think of is to look at the key. If your cam timing is correct don't worry about it.

hawthorne90250 · #7 06-28-2006, 06:20 PM

I have two more quick questions, if i install a 4degree key this would bring my timing back to around 11.5 degrees ATDC,the manual says this is for a new chain, is it ok to bring used chain back to this? also do i install the key to advance or retard the timing? Retard i am thinking?.
Thanks

OMEGAMAN · #8 06-28-2006, 09:34 PM

A 4 deg key would give you 8 deg at the crank so I would say go with the 2deg key.
I dont know the best place to time it at. I suppose the thinking is the new chain will quickly wear a bit and be at the best setting after the wear. My guess is to set at the spec for an old chain.