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01-01-2016, 08:50 PM

#31

ThreeDee

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Join Date: Dec 2015

Location: In the Heart o' the Bluegrass

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Year: 2000

Model: Grand Cherokee

Engine: 4.0

Quote:

Originally Posted by dave1123

The only thing I can think off is the piston skirt length on the 4.0 is rather short from the wrist pin to the base of the piston. This allows the piston to "rattle" up the bore if the clearance gets a little loose.

As I recall, Chevy small blocks have "slipper" pistons in them where the skirt extends down quite a ways, but is cut narrow to clear the crank. This "slipper" keeps the piston straighter in the bore. It's not unusual to see the bottom section of these piston skirts scored up on a very well used engine.

This is just my brain frying, but I think I'm on to something. No drugs involved, lol. The 4.0 does occasionally eat pistons and it's always the skirt that breaks, not the crown under the rings or the wrist pin boss.

And it was indeed a piece of the skirt. Oh, well. At least pistons aren't that expensive, so I'll get one and replace it. I just don't remember where I put my ridge reamer and piston ring compressor. (Of course, this could be my excuse to get a new piston ring compressor. I don't like the one I have.

)

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01-02-2016, 06:24 AM

#32

dave1123

Old fart with a wrench

Join Date: Nov 2010

Location: Manlius, east of Syracuse, NY

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Year: 2000 XJ Sport & WJ Laredo

Model: Grand Cherokee (WJ)

Engine: 4.0L

You may be surprised to know there really isn't that much of a ridge on a vertical engine, having said that, whatever is there should be removed so as to not break the 1st compression ring. What am I telling you for? You've been around engines long enough to know this! I guess I'm too used to talking to newbies.