Jeep knocking at higher rpms?

[Roy Gardner]

A bad wrist pin (loose, missing keeper) or a cracked piston skirt makes these sounds as well. Low compression in one cylinder........ Thats most likely where it is..... It could be in the valve train but I dont think the vac. gauge would hold steady if that were true. A rod bearing, or main bearing would be constant and affect oil pressure at all rpms.
I have listened to both clips and that definately sounds like a broken piston skirt... Careful IMO... its gonna scatter.

 

[Skud007]

Well I scored another AMC 258 i6 / 4.2l , so I'm just gonna swap motors. I have the old motor on the engine stand and will tear into it today. I will be sure to post up what I find. I did find out though that the motor I bought, which was bolted up to a T-4 , will have to have the pilot bearing switched out!! When I measured the input shaft I was measuring the spline part and not the tip, so I thought they were the same.

 

[CJB4POWERBILL]

Ever figure this out ? Mine is tapping too, but yours is a different sound, more like knocking...mine sounds like clicking a ink pen at idle and quitens as rpm go up

 

[Torxhead]

Skudoo7, I look forward to hearing about what you find. PowerBill, your issue could be a bad lifter, which is common for the AMC 258 i6 / 4.2l . It could be caused by wear and tear or low oil pressure.

 

[Skud007]

Well, I have the oil pan off and took a quick look and it seems that some of the connecting rods are a little loose. I haven't dug into it further to see, since I have the other motor in. Yours sounds like it could be the common valve tapping that these motors are notorious for.

 

[Skud007]

Or as torx has just mentioned a lifter. I think thats what I meant to say :-)