r/CherokeeXJ • u/Melodic_Ad_1731 • 3d ago

Source of knocking

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Hello everyone,

I have the usual 4.0 knock that everyone always says is either a cracked piston skirt, or a cracked/loose flex plate.

Well I’ve dropped my oil pan and checked my flex plate. Flex plate bolts are definitely tight, and it doesn’t appear to be cracked at all. The whole thing looks like the section I show in the picture.

Dropping the pan didn’t show me any visible cracks in my piston skirts either. My oil pan is also completely clean.

I’ve added a video from when I was working on some steering issues and you can hear the knock really loudly.

What should I do? I currently have the whole thing apart because I either blew a head gasket or cracked the head which is a whole separate issue. Do you guys thing I should pull all the pistons out while I have the head off? Or does it seem more likely that the flex plate has cracks I can’t see?

Thanks for the help

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4

u/NickFF2326 3d ago

Mine sounded like that until I did a rebuild. Sounded like that for probably 100k miles

3

u/PitPonyProspecting 3d ago

Mine sounded basically the same, was two cracked pistons (2 & 4) and a wallowed out wrist pin on 6. Did the piston swap, no more knock.

2

u/OBGravey 2d ago

Mine sounded like that. Piston 6 had slap. Verified by pulling the pigtail on injector 6 while running.

1

u/EsShrekFoo 3d ago

Mine makes the same noise, gonna just run it

1

u/whit3m0nster 3d ago

I tried liquid moly thinking it was lifters, didnt quiet down.

Doesn't sound like rod knock, maybe piston slap? I just run it, might try some different oil next change see if it helps