Piston skirts

I was talking XJs with a guy who owns his own shop and he mentioned the 2000+ 4.0L's had a common problem with broken piston skirts. I've heard of a few broken skirts but they were in a '98 and '96 4.0L. He was convinced that it is a "common" occurrence in the later 4.0s. I doubt this is true, just wanted to see what you guys thought. Are there that many piston issues?

The only issues I can think of on later 4.0s are the 0331 heads (1999-2002) and the cam sensor/oil pump drive gear on the '05-'06 4.0s. :dunno:

i have a 98 xj and had the skirt break on my number 2 piston around 198,000 miles,it was an easy fix with 6 new pistons,rings and bearings (which were just starting to show some copper on the lower bearing)not to sure if it is a common problem or not though.

4.0s do tend to have piston related problems. Not particularly the 2000+. 2000+ like to crack heads.

Friend of mine with an 01TJ cracked a piston skirt. Drove it 200 miles without it ...

My 2000 broke a piston skirt on #5. Drove it ~200 miles home and parked it in the garage. The next morning... that was it.

Anybody know what causes this to happen?

The usual cause for dropping a skirt is piston collapse from overheating. The piston expands when it heats up, and if it gets too tight, it pushes the skirts in at the bottom. Eventually those stressed skirts can crack, and eventually they will fall apart.

I wonder if the number of skirt problems on late models is related to the head cracking and subsequent overheating.

Some 4.0's do have a lot of piston slap, which is usually benign, and caused by too much skirt clearance, which usually improves when the engine gets hot. Now I wonder if an attempt to cure that might have made some 4.0's more sensitive to overheating.