ukimonster53

How does one go about doing this?

RLXXI

Pull the engine apart and rework the cylinders, then depending on the cylinder diameter a new piston is matched to the hole.
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moparado

This ^^ Is the right way to do it. And don't forget to replace the rings with new ones.

Sometimes adding a thicker weight oil or a oil thickener something like STP can quiet the slap a little for a while but its only for a short while.
A cracked piston skirt can also cause slap and can be a time b0mb in the waiting.

ukimonster53

thanks - I've never taken an engine out so kind of afraid to do it. any idea of how much that would cost $ at the avg dealership or mechanics?

I know it's a ton of variables to consider...

chimmike

I hope this isn't on your 2018 in your signature!

ukimonster53

nope! should've clarified, on an older car.

RL1990

I don't think it hurts the engine, at least it doesn't in GM engines. I have a friend with the 5.3 V8 in his truck and that thing has slapped it's way past 200,000 miles and he says it's been a great truck.

RLXXI

Way back 10 lifetimes ago it seems, my brother and I rebuilt the 351W in his 76 Mercury Cougar. We were both enrolled in the local college for automotive repair so we figured it would be a good learning experience as neither of us had at that time done anything like that before.

The school instructor gave us the go ahead with full shop use, long story short my bro grabbed the ridge reamer without checking the blade and went to work on one of the cylinders, wasn't but a couple secs when he realized the bad blade had gouged the cylinder wall.

So he went to town on it with a cylinder hone thinking he could smooth it out and he did, that cylinder looked like a professional machine shop worked on it, even the instructor came over and had a look and was impressed with the cross hatch hone pattern.

Put the engine back together and got it running smooth as a swiss watch but we both neglected to check cylinder bore diameter and sure as hell it had piston slap. He ran the car another 10,000 miles to the point were he couldn't stand the noise as it had gotten progressively worse over the miles.

When he pulled the engine back apart (still running fine) he found pieces of piston skirt in the oil pan. Had he run it any longer that piston would have come completely apart and left him with gouged (un-repairable) cylinder wall damage due to the rod beating on it.

Measured the cylinder in question and it was .030 over sized. Put in a new larger piston and he drove the car for many more years until some dim wit side swiped it while parked essentially totaling it.
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moparado

Yep^
Piston slapping with a still intact piston if bad enough can sooner or later result in a broken piston skirt and then a grenaded (call for the hook) engine.
Piston slap is a sign the engine is likely on its last legs or something is broken inside which in either case i would not trust that engine for trips longer than to the local convenience store.

EDIT: Your story sort of reminds me of the first time i replaced the piston rings in one of my Harley engines.
When i had the engine all back together it ran fine til it heated up and tended to seize.
Seems i forgot to check the ring end gap clearances.
Had to tear that engine all apart again. What a PITA learning experience that was.

moparado

OP'er,
are you sure its piston slap you're hearing?

Piston slap typically quiets down just a little when the engine is at operating temperature.
Thats due to the cylinder, piston and rings expanding with heat.

Could also be other things like a cracked flex plate, rod knock, crank end play, worn timing chain, bad lifter, something knocking against the frame, etc.
You might want to stethoscope the noise to verify.