Just bought Jeep, Engine Knocking at idle?

I'm new to this forum and after owning newer jeeps and yotas I just purchased a 66 cj5 with the dauntless to make into a trail rig. It has the usual rust in the floors and hat channels which i plan on adressing later. After trailering it home, I finally got it started and noticed that it seems to being knocking at idle. It appears to be coming from the passenger side top part of the motor. As the rpms increase, it goes away. There is enough oil and good oil pressure. I was hoping I wouldn't have to tear the motor down for a rebuild. Could this be a stuck lifter? Rod Bearing? Any ideas would be appreciated.

 

Originating from the top end of the engine could be piston slap or wristpin knock. Piston slap usually happens when the engine is cold and will tend to diminish somewhat as the engine warms up and the pistons expand. Wrist pin knock will sound like a double knock as the piston goes up to TDC then reverses direction.

 

By the way. Anything associated with valves will normally make a tapping sound. Knocks are usually associated with pistons and bearings.

 

A rod bearing will be loudest when you let up on it after reving it up. A lifter will show up in a compression test because the valve will probably not be working right. You could remove a plug wire one at a time to see if engine idle changes. If it does not, their is something wrong with the cylinder which does not produce a change. Knocks are not good things....

 

My '66' was pretty noisy at idle. As the miles accumulated the noise got worse. Turns out the timing chain didn't get oiled very well and would make a lot of noise. One even broke.

I put in a crate engine at 120K and this engine doesn't have the problem.

John

 

Marvel Mystery Oil can help with noisy lifters by helping clear the gum and gunk that is keeping the lifter from fully expanding.

Couldn't hurt either.

Change the oil. Don't use 5-30 its toooooooo thin.
Detergent 30W probably would work.

 

My guess would be a rod bearing. Or possibly a crank bearing. I have a 87 dakota with the same problem. It has the 3.9v6, two years ago it got a nock. After me driving back and forth up north snowboarding (3 hour drive there and the same back) lets just said i made that trip easy over 20 times. Close to the second to last time i started to get a little nock. I didnt think much of it. It got a little louder and since then has been the same for the past 2 years. I occationally took it to the trails and it still hasnt let go. Might i add theres 300+ K on it (odemeter stoped at 93k 15 years ago) Point being its still running.

What ive found helps.

As long has you got good oil pressure and your not reving it to the moon it could last pretty long depending on how loud it is.

ive noticed to run a extra quart of oil in it will quite it down a little.

Does the noise go away when you rev it? Also do the screw driver test and put it on differnt spots of the motor to see if you can pin point the spot its at.

Hope this helps a little.