neonzion

Yeah yeah another knock thread, remember im a desperate poor and very busy 19 year old college student. I was sure my knock was the flex plate but now I dont think so. I bought this XJ 2 weeks ago with a knock, perfect condition otherwise with 121k miles. I hoped it was the flexplate but after bringing the 4.0l to operating temps, im pretty sure its not. The knock is pretty quiet at idle but with a quick rev, its sounds most def like its coming from the center of the head. This friday i plan on removing the oil pan and valve cover, WHAT SHOULD I LOOK FOR??

Radi

Did you actually check the flexplate bolts by pulling the dust cover and putting a wrench on them? If not, do so- it isn't too difficult. Might save you pulling the pan and valve cover.

neonzion

its def not the flex plate, i will check again tomorrow, but the knock is worse now, im pretty sure its a broken piston skirt

Radi

How did you rule out the flexplate? It's right next door to cylinder #6, one of the more likely cylinders to lose a skirt. May well get worse quickly as the bolts continue to loosen.

If you unplug the injectors (or sparkplugs- use a non conductive puller so you don't get whacked) one by one, the noise should change when you unload the offending cylinder if it's a skirt, bearing, pin, etc.
Got a recording by chance?
Might also whack the bottom of the oil pan and see if you hear chunks of metal bouncing around in there. Definite check is to pull the oil pan and take a look.

neonzion

because the sound and the knock (which is a hard clank) sounds and absolutely FEELS like its right in the head between 3-4, so idk what that means. i will try pulling, sounds like a great test! and thats why i had planned to remove the pan, although when i changed the oil, no metal bits came out