We purchased this 1979 300SD in June. I never thought a thing of it knocking when idling cold. However, after reading many many threads, it seems like this is not normal? I get a list of possible problem: injectors, prechambers, cam chain stretch, start of delivery timing, to name a few.

My question is: is anything getting hurt? Eventually (within the next six month - year) I plan to inspect the cam chain and tensioner, get the injectors tested and or rebuilt or replace, and even pull the prechambers. But, how long can these things wait? However, I don't really have that much free time and what free time I do have needs to go into my Volvo 245.

you get a person with a lot of benz diesel experience to listen to it. the diesels are noisy compared to gas engines. even as a very experienced diesel guy sometimes i wonder if it sounds right or not.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well it's fairly common on these old diesels. The knocking could be a number of things, but I'd start with some Diesel Purge. If it quiets down immediately, then you've eliminated the possibility of a mechanical knock, and you're dealing with a combustion knock. Essentially it's caused by delayed, sudden combustion and it could be fuel related (injector spray pattern, filthy prechamber, low cetane fuel, bad timing, etc.) or compression related. If the engine sounds good when it's warmed up I wouldn't sweat about it. These engines are durable, but they do prefer higher cetane fuel than is available at most places. Try some cetane additives or biodiesel.

__________________
2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Knocking or nailing?

Just my opinion, but anybody who attempts to diagnose a diesel engine at stone cold idle is out of their mind. Many 240D's wont cold idle at all according to weather conditions, thats why they've got a manual throttle knob for idle control. And more primitive diesels are not even drivable when cold.

If this is your first Winter with your 116 then expect radical differences in how it starts up and performs from cold start. Now's the time of year to think about using fuel additives too.

Otherwise how many miles and what's the service history? Chains and injectors can become an issue at/near 225k miles.

Hey Tabor,

Lets meet up for food or something sometime and I will have a listen.

I have a good ear for nailing vs. knocking and we can rule out one or the other.