Robert Rausch

This has been going on for months. There is a hollow knock or tock coming from my engine area. It is intermittent, clearly audible at lower rpm's, not at all audible when accelerating, only sometimes audible at higher rpm's. I hear it most clearly when the engine is warmed up and when I'm going 30 with a very light throttle. If I push the pedal down at 30 mph the truck accelerates normally and the noise goes away for the time being. Truck has 389,xxx miles. I've never missed an oil/filter change. Valves were adjusted 4 years ago. Lift pump is not leaking. My mechanic took a cursory look at the truck today, but will do a more in-depth inspection Thursday. HELP!

patdaly

Have him use a stethoscope and listen closely to the area around the lift pump. If I remember right, didn't you just change yours? Anyway, when the spring either gets weak or breaks, the pump doesn't follow the cam and makes the sounds you describe.

Robert Rausch

Thanks a billion Pat. I've been worrying its a rod knocking.
I didn't just install the lift pump--I did buy a good, Made-in-U.S. one, but haven't installed it yet.

Robert Rausch

Just out of curiosity, what is the normal effective life of the rod bearings? Anyone know?

deere country

I beleive cummins states 300,000 miles or 6,000 hours. John Deere states in the 5000 hrs range. Do people get more than that out of them, yes but that's a manufactures recommendation. Much like an oil change some go by the book and some short and some long.

AlpineRAM

Tore down a Cummins B-Series 12V from an excavator that had always followed the recommended oil change intervals.
At 22500 hours the rod and main bearings were still within the service limits.
Pistons and rings still OK, (slightly out of spec).
Valve springs out of spec, valve guide bores way out of spec.
Cam was worn.
Reason for the teardown was a head gasket problem caused by a faulty radiator cap.
Since you have to pull the engine to remove the head in that machine, we tore it down.

Robert Rausch

Good news. The noise was from a fuel line out of the lift pump that was knocking against something and making the racket. My mechanic secured it and now, no noise.

patdaly

LOL, that's more like it, you have a loooonnnggg time to serve before your Cummins lets you down.