Help! Flex Plate or Rod Bearing or ?

I have been trying to diagnose what sounds like a rod knock, here is what I have:
91, 4.0, aw4...

I have checked the four 15mm bolts on the fly wheel, all tight, I cannot see any cracks but I am not sure you can even see the flex plate by just taking off the cover...

I have drained the oil and put in 60 weight oil, made no difference.

The knock gets louder as you raise the rpms, this is a loud knock!

When the engine is cold it is barely noticable at idle...

SO, any ideas, I would like to try and eliminate the flex plate or know for sure that is what it is, as it is the biggest job to replace...

Thanks,

Dan

Could be piston slap, but I'll tell ya'....I had what e-1 said was a rod knock, borught it in to have TC changed, while in the process the mech. checked everything for tightness and found that i had a cracked flex plate, replaced it and my XJ (90) quieted right down, so don't just give it a quick visual, turn the flywheel and feel it for cracks, have plenty of light too..... a lot easier to replace flexplate than rebuild eng........good luck.

swaped my tranny 4000miles ago, i got a knock about a week ago...

i thought i had been pushin my motor alot lately and got scared cuz the sound was comming from the oil pan

i took off the flex plate to check the bolts on the torque converter cuz i heard about others loosening up, all 4 were loose and 1 was abou to fall out... only thing holding it in was the constant contact with the flexplate ....heh


mine also stopped making the noise when in 3rd gear and overdrive

JVRacer...

You pulled the tranny to get to the flexplate?

We pulled my tranny, but I was cahnging TC at same time and had a prob. with one of the top bolts, did make the job easier though with the tranny out of the way

The flex plate cracks in an annular (circular) crack, not radial. The crack is typcally right around the outer perimeter of the hub reinforcing ring. You can see it move if you remove the inspection cover and pry against the edge of the flex plate.

Basic test -- put the tranny in gear with the brakes on and give it just a little bit of gas. If the knock disappears, it's probably a cracked flex plate. If the knock stays or gets worse, it's probably a rod bearing or wrist pin.

dwebb944t said:

JVRacer...

You pulled the tranny to get to the flexplate?

Click to expand...

no i convert to 4WD and put in a whole new AW4... mine was shot with 230,xxx

but since i didnt go back and tighten everything down.. the flywheel bolts got lose

If you need a flexplate I have one out of a 97 that will work fine (40k miles) sell it for $50 plus shipping. New ones run about $100.

If you think it's piston slap RESTORE will quiet that down. All six of my pistons on my 96 sounded like a diesel at idel. Restore silenced most of it.

JoBo

I pulled the pan after checking the flex plate and using a stethoscope to pintpoint the sound, the # 2 bearing was shot, all the rod bearings are worn. Thanks for the help guys...

Dan