'89 2.5L - sounds like a diesel

'89 Comanche, 2.5L, 2wd, 5 speed 170K+ miles.

Engine seems to run pretty good, with a bit of a "rythmic miss" in the exhaust but really loud under/around the valve cover - sounds just like a 4cyl diesel injection pump rattling away.

Pulling the spark plug wires one at a time didn't affect the noise at all.

Higher RPM's make the noise almost go away.

I removed the valve cover and there's plenty of oil getting to the valvetrain. Nice and wet under there - and surprisingly clean too.

Noise seems to be loudest toward the front/top of the engine but hard to tell - it's friggin' noisy at idle.

I removed the rocker arms, push rods and lifters from cylinder #1 and I don't see any unusual wear to any of the surfaces. Looked down at the cam lobes and they appear fine as well. When tightened down and rotating the crank, all 4 cylinders appear to have good open/close motion at the rockers/springs. The rocker arms are pretty tight - hard to get them to "wiggle" at all even when at the low part of the lobe. Push rods are snug, but will spin by hand until loaded.

Read a thread over on Comanche Club forums that the "diesel" noise has been found to be a loose timing chain? Anyone else had this experience? Maybe my valvetrain is fine and the "rythmic miss" I'm hearing is actually some poor valve timing caused by the loose chain?

Thanks in advance!

Timing chain?

I had the chain tensioner go bad in mine a couple years ago. Is yours quiet when you first start it up (cold) then start to make the noise as the engine warms? If yes, then I'd suspect the chain. I screwed around trying to diagnose the noise for the better part of 6 months until I finally decided to pull the timing cover.

I've got a writeup on here somewhere....lemme see if I can find it and I'll post it up so you can see what my problem was.

Jeff

edit: here ya go....http://www.naxja.org/forum/showthread.php?t=903937&highlight=*timing*

I had the same problem with my YJ 2.5... I replaced the timing chain and tensioner and key it still sounded like a diesel.

The problem on mine was the domed washer in between the crank and the crank pulley. It was smashed completely flat... I guess from one to many hits with an air gun.... The crank pulley rattling was the noise.

I replaced the washer with a new one, it crushed down nicely, the pulley was firm and all was well. Sounds like a new vehicle now.

Why do anything? I love how diesels sound....

Jeff in VA said:

edit: here ya go....http://www.naxja.org/forum/showthread.php?t=903937&highlight=*timing*

Click to expand...

Thanks Jeff! I imagine it'll be the timing chain.

I have no experience withis motor but the guy talking about the loose crank pully, that sounds like a potential source too...

I know the pully for the water pump on my 95's 4.0 cracked (not the actual pully with the bearings, but the pully "cover" that bolts over the water pump pully, where the belt rides)

Anyway it had cracked and was making my motor sound like a diesel at idle. Here's a pic:

Well, indeed it was the timing chain!

Nice and quiet now.

:thumbup:

:cheers: