Hello All, I drive a 1993 300SD. This is my first Mercedes and first diesel so its a learn as I go experience. I am aware of the problems with this engine and hope this is not related. The engine has a loud clatter and lopes at idle which disappears completely at 1400 RPM. From there on up its smooth as glass. I have just 100,000 miles on it. I suspect this may be just a simple valve adjustment issue but would appreciate any insight. Thanks for any input.

 

The clatter you describe sounds like it might be a fuel knock, check for air in the fuel system including fuel return lines, restricted fuel filter, restricted air filter. If all of that checks out ok then check your injectors, and or injector pump. Too much air and it won't start, but it can pull a little air and cause the dreaded fuel knock. If the pump isn't sending a full charge of fuel to the injectors they can't give enough to the corresponding cylinder. If the injectors are sticking they won't fire correctly, and you will find most of these troubles when idling untill they get bad, then it will have problems idleing and knock at the higher speeds Good luck

 

The bent rods that I've had experience with haven't lost thier knock at higher rpm, maybe it's because I've seen most of them after the piston skirt has already collapsed and the knock was pronounced, and continious. I will agree that a fuel knock can be confused with a beginning stages pin, or rod knock; however the knock usually dosen't go away with rpm due to the fact that something is loose in there.

 

The car cruises silently at 80 mph all day. Would either a fuel knock or bent rod show at this speed. I will check filters first as this is the simplest. I did replace seals on injector pump, injector return lines and one injector recently due to leaking. Knocking was present before and after. Leaks are fixed. No change in performance or noise.

 

I would think that very much of that and your "bent rod" would be sticking out the side of the block. I would suggest that you get your injectors tested for output, and see at what pressure they fire at. You could have low compression on one cylinder, but that is as unlikley as a bent rod. If the simple stuff dosen't work, get a compression test done and see. If there is low compression, and it suddenly showed up, I would suspect a burned valve, long before a bent rod.

 

I'll admit that I am in-expieranced with the MB engine in particular, but are they so poorly built that they will just bend a rod without any reason? Usually a bent rod comes from an internal collision, carbon build-up, tip of a glowplug in the cylinder, timing chain stretch, ond/or gear wear causing pistons and valves to meet. 93MBW140 made no mention of any of those possibilities, unless it was in a previous post.

 

I am not experiencing any excessive oil consumption. Assuming the worst and it is a bent rod and also assuming that everything else is maintained properly, what am I looking at as far as engine failure goes. Can I expect a slow decline over 50000 miles or a catastrophic failure at any moment. I have several vehicles and drive this one about 8000 miles a year.

 

What ForcedInduction is saying is VERY possible, to check that out run a compression check, the cylinder with the lower compression is the one that is the problem. If you run this very long it will wear out your cylinder to the point that it will need to be bored out, and possibly sleeved, if the block can even be saved. If your compression checks out ok then check your injectors, then your pump

 

if you need cheap parts, like push rods, you should check out iPartCars.com....this way you can test out to see if thats the problem rather then spending for a new ones...and if its better than you can always spring for new parts when you pinpoint the problem...i usually try used parts when im not sure of a problem, its better than throwing out good money after bad. just a suggestion.....