Jeep knocking at higher rpms?

[Skud007]

Hello, I've just joined the forum and have introduced myself in the introductions. I am happy to be a part of the forums now!

The issue I'm having with my AMC 258 i6 / 4.2l is a knocking sound @ around 2000 rpms and higher

I've searched this forum and plenty others and still haven't found a relative answer. I've come close but the other problems I have read about aren't quite the same or they were never answered.

The engine doesn't knock at idle or anything below 2000 rpm when accelerating up to that point. I began to think it was a preignition or detonation. I have never really heard preignition before, but have heard it compared to marbles in a tin can. Mine definitely has more of a knock sound to it. I have performed the team roush dist. upgrade and i'm running a stealth gm hei. I'm running at about 9 degrees advanced timing. I performed a compression test and from what I remembered my lowest reading was 110 and the others around 120. Vaccum reading is steady at around 15"hg @ idle (at 5280FT above sea level) and snaps to 0 when the throttle is opened, so it seems the engine is sound?

It seems to mellow out a little when I unplug the distributor advance vaccum. I have tried to adjust the little allen screw in the distributor advance so it takes a little more vaccum to advance. I don't remember what I set it to? I'm thinking around 4"hg from the stock setting of 2"hg???

After picking up a mechanics stethoscope it seems the sound is coming from the front of the engine. That led me to believe that it could be a loose timing chain? Wouldn't a loose timing chain make a knock more at a low idle than that of higher one though if it were loose? Also if it was a rod knock wouldn't it do it at idle??

I'm planning on taking some video of it hopefully tomorrow and posting it up.

Any ideas??

 

[Torxhead]

One way to check for a loose timing chain is with a timing light. When the light is flashing on the timing marks, with the enging running, it should be steady at the degree mark. If it is bouncing around, this would be an indication of a loose chain.

 

[Skud007]

One way to check for a loose timing chain is with a timing light. When the light is flashing on the timing marks, with the enging running, it should be steady at the degree mark. If it is bouncing around, this would be an indication of a loose chain.

Thanks Torx! I know for sure it is steady when I adjust the timing at idle. I'll have to check it at higher rpms or when the knock starts. I'm off work today, so I'll check that and try to get a video up!

 

[Skud007]

Here is one video:

http://www.flickr.com/photos/7512624@N06/8331213692/

I'll take another video driving around because it seems to do it more under load.

 

[Tinman22]

Sounds like its at 1/2 engine speed and very rocker armish the rocker/pedastal design is really trouble free till it wears out then it starts to dance at higher rpm. Listen to the valve cover. Bet ya donut the noise is over the cyl with low pressure.

 

[mtnwhlr]

The AMC 258 i6 / 4.2l has a problem with the #6 rod spinning the bearing.

 

[Skud007]

Thanks tinman ill give it another listen. I have another video here of it while I'm driving.

VIDEO0008 | Flickr - Photo Sharing!

When I drove it this morning to work it operated smoothly, other than the engine knock. I did let it warm up about 20 mins before I left. On the way home it started sputtering and stalling, especially around corners . Thinking that maybe I didn't let it warm up enough before I left work I figured that was the problem. It did it most of my 20 mile commute.

Thinking maybe the carter carb was at fault, I put my 2150 back on, that I had previously taken off to pass emissions. Still same thing stalling and sputtering and the tachometer jumping around crazily and knocking at the higher rpm.

It had this problem when I first bought it with the points type ignition. It would barely get up to 40 and over 1400 rpm. After I performed the team roush and gm stealth hei upgrade on a new '85 jeep distributor it ran well. That was when the weather was a little warmer. It has been in the mid to upper teens here today.

I'm about ready to start looking for another I6 to drop in this thing!! LOL

 

[Skud007]

The AMC 258 i6 / 4.2l has a problem with the #6 rod spinning the bearing.

I've never hear what a spun bearing sounds like? Does it do it all the time? It really sounds decent at idle other that the common noisy lifters.

 

[mtnwhlr]

It's a rod knock I think the more you drive it the worst it will get. My first CJ I bought and it and it did it all the time and it was bad. But just saying thats what I think it is.

 

[Skud007]

It's a rod knock I think the more you drive it the worst it will get. My first CJ I bought and it and it did it all the time and it was bad. But just saying thats what I think it is.

That's what I was thinking too mtn when I first heard it. I tried probing the stethoscope around the sides of the motor and it just doesn't sound like it does when I probe it around the front of the engine?? I haven't had a second set of hands to probe around the oil pan yet.

 

[mtnwhlr]

I'm not to far from you maybe I can help you out let me know.

 

[Tinman22]

Wow yeah that second vid sure sounds like a bearing doesn't it !!! Easy enough to drop the pan I guess.

 

[Skud007]

Thanks for the offer mtn!!! Not to sure when I will get to it since I have another running vehicle. When I do get to it, what should I be looking for when I drop the pan.

 

[mstar]

It's a rod knock I think the more you drive it the worst it will get. My first CJ I bought and it and it did it all the time and it was bad. But just saying thats what I think it is.

Another vote for "rod knock" mtnwhlr is right on ! Mike

 

[Skud007]

Yep!!! I've been youtubing videos and it sure sounds like it I figured I was ok since it didn't do it at idle.

 

[mtnwhlr]

When you pull the pan look for a rod that has more play than the rest of them. I will bet its the #6 if you pull the cap off you will see cooper on the bearing.

 

[hagar]

Sounds like rod knock to me.
If you didn't have the HEI, you could pull the plug wires one at a time while having someone hold the throttle steady and by wire pulling figure out which cylinder.
Sorry for the bad news, but I believe rod knock.

 

[Skud007]

Sounds like rod knock to me.
If you didn't have the HEI, you could pull the plug wires one at a time while having someone hold the throttle steady and by wire pulling figure out which cylinder.
Sorry for the bad news, but I believe rod knock.

Its ok now I can swap in that 4bt!! LOL

 

[CRETE4U]

4bt. Now you're talkin. One way we used to test to see if it's a rod knock. Put it in high gear with the clutch in get it to the point where it knocks the loudest and let off the clutch just enough to put a load on the engine. If it's a rod it will stop knocking. Pan needs to come off anyway though.

 

[Skud007]

Well, I still haven't got around to pullin' the pan but I scored a whole AMC 258 i6 / 4.2l , T-5 , and 300 for a reasonable price so I'm just gonna pull the motor and replace it with the other. I will definitely post up what I find out with the original motor when I dig into it.