My 98 12valve has always had a noise, since I picked it up at 175K miles. I thought that diesels were just noisy. I then damaged my injector pump with bad fuel, and blamed the noise on the pump. I have now replaced the pump and still have a noise.

On a different note, I have an ancient lincoln welding rig, that has a 4 cylinder continental engine on it. It made a noise, for a long time. I ran it anyways. I recently had to tear it down and found a spun bearing on #1 connecting rod (a-ha! there is the noise source). Since it is put back together and fixed it is smooth and quiet.

Now I am wondering if I am ignoring a noise that could be serious from my precious 12 valve. When listened to from the bottom side you can hear a distinct thunk, thunk, thunk... in rhythm with the engine RPM. Good oil pressure... Could a more astute mechanic determine the noise with a stethescope or "listening stick"... Could I still have an injection problem like out of balance injector pop pressures, and that would sound like a knock. Being second hand, someone else could have abused it, I guess. I don't have any odd oil consumption. The truck seems "tight". I don't want to be naive about a knock though... Thanks in advance.
-Greg
BTW running around 275K mile now...

 

Put a stethoscope on the lift pump and see if it isn't the source. They are noted for ticking.

Doubt you have a rod bearing, with the combustion pressures of a Diesel, I doubt it would live very long at all.......

 

No way it would run for 100k miles with a bad bearing

 

Using the search function, I read a few other similar questions. Some reported that a bad oil filter would plug an orifice oiling the #6 wrist pin.
It is an interesting thought about the lift pump. It is stock, and hasn't changed. I will have to see if I can pin point it to that.

A wrist pin would be a pretty deep part to repair.
-Greg

 

Eh, pull the head and the pan, and drop one in.......

 

Yeah! Lay out all the tools and gaskets so you can have it all buttoned up before the coffee gets cold...

Piece of cake!

Patdaly, do you think that a knock from a wrist pin could go for many, many miles? Thanks

 

I don't know how you would "shut off" one cylinder on a diesel, but on a gas engine you pull the spark plug wires one at a time, when you pull the one on the cylinder with the problem, if it's the rod bearing the noise will almost go completely away, if it's the wrist pin, it will get a lot worse. I would think you could unplug the injectors on a CR engine, but no clue on a mechanical one?

 

A wrist pin will usually sound like a very quick double knock. They make a noise when they hit the top then again when they start back down. I am pretty sure it wouldn't go that long with a wrist pin knock either, but stranger things have happened!

 

Other than perhaps a valve being out of adjustment or a lift pump, I can't think of much that would last very long knocking on a diesel........... Guess it could be an imbalanced Injector, you could always try loosening injector lines while it is running and see if the knock goes away.

 

That's the only thing I can think of as well, however without hearing it it's really hard to tell. Some people's description of a knock can be different than others.

 

Ain't that the truth, the first year I owned Brownie, the lift pump started ticking.............. Sounded like it was coming apart to me.

Now, just sounds like a lift pump......