1985 300CD New Timing Chain = Shocking Benefits
 

Today I replaced the timing chain on my 300CD. I also adjusted the valves, changed the oil, new coolant, new glow plugs, new air filter, and a fresh bypass hose on the thermostat housing to water pump housing.

Before doing these repairs, the car ran ok. It had kind of harsh shifts and I had to keep the idle set to 800 to keep it smooth. There was also excessive smoke from the tail pipe.

After finishing things up today, the shifts are smooth and the power/pick up is far better than I was hoping for. I need to wait for daylight to adjust the idle back down to 650-750 and readjust the rack damper bolt while I can see any changes in the smoke at the tail pipe.

I'm curious to see how this is going to effect fuel mileage.:cool:

Cool

Did you happen to check the stretch? Sounds like it may have been substantial.

Getting the power back does make the trans shift better. It basically puts the travel of the throttle linkages in optimal adjustment to make it shift better.

Great job!
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I had the same results when I had the chain replaced on my SD several years ago. It had 10+ degrees of stretch, and was transformed with the new chain, 100k later and its still running awesome. Significant pickup and power delivery increases were what I saw with the replacement.

WOW 10° stretch!!! I'm amazed you did not need new gears with that much wear! have you measured stretch since the new chain is in?

"new gears" for what? ...because of chain stretch. not getting the comment.

Stretch is wear and sprockets will show a proportional amount of wear.

I have never seen 10° of wear in a chain, and I have done 617's with the aluminum tensioner shoe almost cut in half by the chain.

For clarification, I am not doubting you, I have just never seen a 10° variance personally from wear alone....

I did the same job not too long ago, but the difference was not significant enough to me. The timing chain job was past due in my case, with the car at 235k+ miles at the time the chain was replaced.

http://www.peachparts.com/shopforum/diesel-discussion/328442-w123-timing-chain-replacement-photo-references.html

When I got my car in 2004 it already had a 3.69 differential. So it's been screaming its guts out at highway speeds until 2008 when I was able to source the correct 3.07. I wasn't able to check the difference between the chains though.

I can't wait to get the 2.47:1 in to replace my 3.07:1 axle!!!!

Out of curiosity, why do you attribute the smoother running to the chain replacement alone? Wouldn't the valve adjustment and air filter also play a role in this?

Because I've maintained this car for the past five years and never had an air filter or valve adjustment make these improvements. It was only 5k miles since the last valve adjustment. I just did them again since the valve cover was off for the chain. The valves were only slightly tight.

4° but I checked it with the marks on the cam so I don't know how accurate that was.