4.0 Piston Skirt Breakage

[jsawduste]

Seems an epidemic of 4.0`s breaking skirts here in Mi.

No rhyme or reason. Some of the engines have relatively low miles while others are 200 +. Seeing this in XJ`s of 96 up most often but not limited to. Perhaps more XJ`s as there are more of them being used in our area then other models. Mostly all automatics that are DDers for the most part.

Have some thoughts and theories but was curious what the stroker gang might think.

[ruffy01]

Just last week my '96 developed a horrible engine noise. Doesn't appear to be a collapsed lifter nor a big-end noise, I'm thinking a broken piston.
Will know for sure in a few weeks when I have time to tear it down.
Engine has done 348,xxxKm's (~220,000 miles), was running perfectly, stopped at a shop, restarted and the noise was there

[Cheromaniac]

Amongst the modifications DC made to the 4.0L engine for the '96 model year was the addition of lighter weight pistons, and does indeed appear that these are more prone to skirt breakage than the earlier versions.

[Retlaw01XJ]

My '01 had a broken skirt when I bought it a few years ago. Only 107,000 miles. Other internals looked nice. Got it cheap so it was a natural for a stroker build.

[amceaglesx4]

But why lighter pistons ? All a piston does is go up and down. If it was shaking side to side it could make more sense !

[Russ Pottenger]

But why lighter pistons ? All a piston does is go up and down. If it was shaking side to side it could make more sense !

A piston does more than going "up and down"

100 page tech manual could be written on piston design and all the technical aspects of use and application and still not even come close to answering all of the questions regarding a properly designed piston.

[amceaglesx4]

I had no idea a piston was so complicated. Everyone Ive ever have seen looks the same basically. But...doesnt a piston just go up and down. What else do they do ?

[SilverXJ]

But...doesn't a piston just go up and down. What else do they do ?

Then why not just use some coke cans?

Some other things the piston does:
-skirts keep it from flipping over in the bore
-The sides have a cam grind and are not just flat
-Keeps combustion in the cylinder
-Keeps the rings in place
-Helps properly ignite the air fuel mix
-Holds the piston pin
etc.


It is not just a simple piece of aluminum

[amceaglesx4]

Never thought of those things. Guess i didnt think that much into it.

[MunkMaster]

At about 213xxx 2 different skirts crumbled. One was minor and the other one was almost all the way up to the piston head. Really sucked especially since I had just rebuilt everything above the block 5k before that happend. And no it wasn't related.

[MunkMaster]

Here is the damage

IMG_20170513_112019711.jpg

[Muad'Dib]

What kind of pistons? Stock cast?

[MunkMaster]

They are the factory pistons.

[Mousejockey]

Is there a reliable brand of replacement pistons?
In the midst of a rebuild, going .030 over due to some water damage, block had been sittin

[Russ Pottenger]

I have a piston forging made out of a 4032 high silicon aluminum alloy that because of its material properties it offers great wear resistance, a low expansion rate, is very durable, and very low in friction.

I'm currently offering a package Forged piston and Forged connecting rod deal.
Feel free to shoot me a call and email I'll be happy to give you more product and Stroker kit info.

Thanks,
Russ Pottenger
Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California, 91790
Work (626) 967-1000
Cell (626) 673-2203
Email/PayPal: [email protected]