300D engine noise

[patterson]

I recently purchased a 1983 300D with 351,000 miles on it. I bought the car cheap because the engine is making an odd ticking noise that does not diminish with speed. The noise is about the same intensity idling as it is at speed. I have only driven the car home from the previous owner's home because of the noise. The PO says that is started on the way from Florida and he continued driving it and took it to our local mechanics and none of them could figure out what it was. So he continued driving it he claims to have driven it 10,000 miles since the noise started and it hasn't gotten any louder. The engine doesn't seem to have excessive blowby, doesn't smoke, has good oil pressure, and the PO said that it didn't use any oil.

I suspected that the problem was in the valve train somewhere so I pulled the valve cover and adjusted the valves, all of which were tight and some had no clearance. So the noise wasn't a loose valve. I started looking at the timing chain and it seemed to have about 6 degrees of stretch using the crank pulley as a guide. Also the guide rail at the tensioner seemed to not be aligned with the tensioner like it should be, there was actually a place worn in the arm by the tensioner pushrod where rail wasn't lined up like it should be. The guide rail is leaning back against the block. Would this make the noise that I am hearing some how? and What would have caused it?

I hypothesised that somehow the slack in the timing chain caused this somehow, but wouldn't the timing chain have broken in 10,000 miles of driving. I want to think that this is what is causing the noise and nothing deeper but I am not sure. Thank all of you for any help you can give.

Patterson

[franklyspeaking]

It very well could cause the noise you describe. I had a chain tension rail failure on my 240D and it ran for a long time without any tensioning at all! At the time I was too ignorant about MB diesels to realize I had a serious problem. The car had a recurring starter lockup problem that I later came to realize was the loose end of the chain wrapping itself arount the crank sprocket. It finally broke during an attempted start and I had to learn all about timing chain repairs. But the engine once started ran okay with no abnormal noise. The chain rail had failed at the pivot pin and was just flopping around inside the chain cavity. I estimate it was that way for 6 months and 3 to 5,000 miles.

There is a ton of information in the forum about timing chains, and you should do a search and read up on them. From what I have learned, you have way too much stretch, and your tensioner and or tensioner rail have problems that you need to attend to ASAP. I wouldn't drive it to the gas station with the condition you describe. If the chain breaks while driving, your engine is toast.

Good luck!

[patterson]

Thanks for the quick reply. The car is parked, some people can convince thereselves that a noise like that ain't going to hurt anything but I can't. I turned the motor over and looked at the chain and all the links look to be peened the same so can I assume that this is the original chain? 351,000 would be alot of miles so I guess it should be getting loose by now. I am going to replace the timing chain, the tensioner rail, the pin at the bottom of the rail, and maybe the tensioner. And hope the noise goes away.

Is there any way to check the tensioner to see if it is working? or is it just one of those things that you replace if in doubt.

CHANGE IT ASAP!!! Dont drive the car another foot or if possible even start it!! 5 degrees of stretch is the limit.. your car is a time bomb!

[franklyspeaking]

I don't think the tensioner is much more than a spring loaded rod, but I didn't replace mine, and I don't know even really know how to check it. Perhaps someone will post a reply to educate us on how a correct tensioner looks and feels.

When I got everything installed the chain seemed to be relatively snug and the tensioner was pushing the rail into the chain such that all of the slop was removed, so I was pretty happy with the way everything looked. I have only driven it a few hundred miles, since I changed it.

[michael rybikowsky]

replace all of it rails tensoner etc.

[patterson]

I have the all of the parts and plan to work on the car this weekend. The new tensioner rail I recieved has a plastic coating on the side that contacts the chain. The one in the car has no plastic on it. Did the original tensioner rails have plastic on them and mine is just gone or is this an improvement over the original. If the plastic should be there on my original what happened to it and is it going to cause problems.

Thank all of you for your responses so far.

[engatwork]

The book indicates it as an upgrade.