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Better worn piston longevity using skirt buttons ?

Mikep_86441

NAXJA Forum User
Location
AZ
Tell me if this sounds like BS.

The piston slap that we get is significant when it happens. The videos I've seen are showing what has to create a 1/16" skirt/cyl wall gap. That's crazy.

This xj we just got has at least one piston slapping. I was thinking of trying to extend their life by adding ptfe (teflon) buttons to the skirts to take up the slop. If they wear out, put in new ones. With these relatively low rpm 4.0 engines, I think that a button or 4 on the piston skirt might at some solid life to the worn piston.

I found a rod of this ptfe on amazon for $15. It's 2 feet long.

The head of the button will be tapered so that it can be filed down like a tiny volcano so the skirt of the piston can be fitted to the cylinder bore nice and snug. I bet the 1/4" or so hole in the piston skirt can just be done with a drill press. It will need a counterbore for the head of the button to sit. The holes don't have to be perfect because the button would get filed down to what ever lets the piston fit into the bore.

Just wasn't sleeping and thought of this for when I have to yank the oil pan off and see what's causing the piston slap.

If anyone has a worn 4.0 piston, could you take some calipers and measure how thick the worn piston skirt is ?

Here's a pic I found of a racing piston prepped for buttons.

https://www.rbracing-rsr.com/turbo/bullett/bulbenefit/bulpstn_peek2.jpg
 
Since you have to tear the motor down to fix any of this, why not fix it right?
 
Piston slap isn't forward/backward on the engine, it is side to side and is usually caused by the tension getting weak in the piston rings and wear in the cylinder wall.
 
I was under the impression that real piston slap was caused by a broken, no longer there, piston skirt? Thus not repairable.

How do you know for sure it is real piston slap with out a physical inspection?

THis "The piston slap that we get is significant when it happens." makes think your issue is not piston slap?

4.0s are notorious for loud lifter issues that come and go.....
 
Piston slap isn't forward/backward on the engine, it is side to side and is usually caused by the tension getting weak in the piston rings and wear in the cylinder wall.

You might be thinking of teflon wrist pin buttons. They would be located in the fore/aft direction.
 
I was under the impression that real piston slap was caused by a broken, no longer there, piston skirt? Thus not repairable.

How do you know for sure it is real piston slap with out a physical inspection?

THis "The piston slap that we get is significant when it happens." makes think your issue is not piston slap?

4.0s are notorious for loud lifter issues that come and go.....

Understood. I'll get the answer.

Opinion on the addition of buttons to skirts that are there?
 
GM's definition,

"Piston slap is nothing new to piston driven internal combustion engines and compressors. It is the secondary (sideways or perpendicular) movement of a piston against the side of a cylinder bore where the primary movement of a piston is intended to be parallel (up and down) to the cylinder bore. All piston driven internal combustion engines and compressors have a certain amount of piston slap.

Excessive piston slap occurs when the clearance between the piston and the cylinder bore is too great. The piston to cylinder bore clearance becomes too great either through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The audible noise associated with excessive piston slap is due to the perpendicular impact of the piston against the wall of the cylinder bore. Audible piston slap is typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance thus, reducing the perpendicular impact of the piston against the cylinder wall and its resulting noise."
 
Green Jeep, you are wise in the ways of slapping.


:worship:
 
This is not a DYI project, they are not dealing with used piston/cylinders that are out of round and have a taper(let alone ring grooves)!
bulpstn_peek2.jpg
 
This is not a DYI project, they are not dealing with used piston/cylinders that are out of round and have a taper(let alone ring grooves)!

I think my engine might be a worse case example of using buttons. But my engine also represents lots of other people's 4.0's. Even a better reason to try it.

As for diy, that's in the eye of the beholder. If a person thinks they can do it, they probably can.

Besides, since nobody else has tried, it's worth it to me. What if it works ??
 
:rolleyes:

Nominated.
 
None of us (to my knowledge) have tried suicide either.

But I have used many things like duct tape with good results. Good luck

I think my engine might be a worse case example of using buttons. But my engine also represents lots of other people's 4.0's. Even a better reason to try it.

As for diy, that's in the eye of the beholder. If a person thinks they can do it, they probably can.

Besides, since nobody else has tried, it's worth it to me. What if it works ??
 
Piston skirts are there to stabilize the piston in the bore. When they get worn, they let the piston rock. Ring tension is so light it won't influence what the skirts are doing. This video shows that.

https://youtu.be/VAkmlvW9fYA?list=PLCyDzy-NaUwLw63UOBOnfogiSfJqdfIpF

That engine sounds exactly my YJ right before I had to replace the piston. It started sounding like crap on the way home and was blowing smoke out the oil cap. The wrist pin had seized and gouged the cylinder with identical galling on the piston skirt you see in the video. You can see his wrist pin is seized as the rod isn't moving and the rod is discolored. The bad piston was .04 smaller in diameter than the good ones - a badly overheated piston will end up smaller after it cools down. I replaced the piston, honed the hell out of the cylinder wall and all was good for another 30k miles until I sold it.

Funny to note that the factory put half the rings on upside down.
 
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