Rear Main & noises

Replaced the rear main...and man what a messy job that SOB is...

Glad I did it though...not sure that it was the rear main that was leaking or the rear of the pan gasket...either way we're leak free now. I do recommend that anyone about to do this go with the one piece gasket from the dealer...that puppy was sweet and easy to work with....well worth the extra cash.

The bottom end was awesome....no funky, weird wear on the bearing or journal. Everything was very clean with no amount of sludge to be found...even on the bottom of the pan. There was no funky odor of burnt oil etc...and everything was tight.

I have however developed either a knock or piston slap over the past 3-4K miles...some days it's not as noticeable and others you can really hear it. This makes me wonder if myaybe I'm getting some knocking from the gas I'm putting in...what do you guys think? I really didn't pursue it until I got the rear main outta the way so I could inspect the bottom end at the same time...The engine has 85K, the oil has been changed regularly, never over heated, and only tows maybe 1 or 2 times a year.

Matt

in my opinion, piston slap is either there...or it isnt. Ive run into more sticky lifters than pistons slapping around-only difference I can tell is with piston slap, the noise kinda stays the same 100% of the time, where a sticking lifter makes a higher pitched noise-that gets louder, then disappears...much more noticable at startup when cold.

Piston slap is one of the few noises that will get quieter as the engine gets hotter, and may even disappear when it's well warmed up. It also doesn't change under load, so you'll hear it at idle. Where a bad lifter will go tap-tap-tap, only once for every two revolutions of the engine (for a single lifter), piston slap of the benign sort common on XJ's will usually have a faster beat, and sound more like loose marbles. This is assuming you don't have a collapsed piston or other real damage, unlikely unless you've had a serious overheating incident.

Unfortunately, some other noises blend with the slap and can be mistaken for it, including a bad water pump. So if it set in fairly recently, I suggest you inspect the water pump and pulleys too.

Combustion knock will usually increase under load, especially lugging in high gear, going up hills, etc. If you suspect combustion knock, you could always wait until the tank is nearly empty, then put in some premium gas, and see if it goes away (if you wait until it's empty, you won't have to invest in a whole tank to try to blend it in, a quarter or so will do).

I'll put in a higher octane at my next filling to see if that stops or diminishes the knock...

Matt if I read your post correctly some piston slap is normal in the 4.0 XJ??? The reason I ask is because things sound just as you described....like marbles.

I need to change my serpentine belt and when I do I'll deffinitely check the water pump for any play.

Matt

mdwatkins said:

I'll put in a higher octane at my next filling to see if that stops or diminishes the knock...

Matt if I read your post correctly some piston slap is normal in the 4.0 XJ??? The reason I ask is because things sound just as you described....like marbles.

I need to change my serpentine belt and when I do I'll deffinitely check the water pump for any play.

Matt

Click to expand...

Some piston slap is normal on some 4.0's, but it seems to follow no rules. My 87 had none at all. My stepson's 93 has a little bit as it nears 200K miles. My 95 has rattled and slapped merrily and inconsequentially since I got it, never getting either better or worse between 110K and 223K. My son's newly acquired 96 seems to be slap-free. Go figure.