Pistons/reconditioning

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Captainkirk

Captainkirk

Old School Mopar Warrior
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I'm in the process of cleaning my pistons. Apparently, my engine guy just dipped them in some sort of degreaser. There is some white, powdery residue left in spots, and some light pitting in other spots. This got me to thinking....
First of all, is there any sort of aluminum cleaner I could dip these things in to really get them clean? On some of the aircraft parts (airframe parts, not engine parts) I clean at work, we dip them in DuPont metal etch/cleaning solution, which gets the aluminum looking like brand new. I believe it is a form of phosphoric acid. Any reason why I wouldn't want to use something like this? I could also use ScotchBrite, which will leave a shinier surface. I'm sure it would clean them up well, but not sure if it would weaken the metal.
Then I got to thinking about the mild pitting on the piston skirts (below the ring grooves) and started wondering, again. As a reloader, I know they make spray-on Molycoat for bullets (those are the black-tipped ones) that is an extreme pressure/heat resistant coating. Would there be any advantage or disadvantage to coating the skirts with something like this? Would it interfere with break-in? I'm using new rings with freshly-honed cylinders. I know some of the new pistons come with some sort of coating on them. Any insight would be appreciated.
 
You would have to see how thick the coating will be. Years ago, some guys would knurl piston skirts to decrease clearance in cylinders that were on the big side of the std range. They also said the knurling would hold oil for less scuffing. I don't know if anyone still does this.
 
It's an aerosol spray. I'm sure you could make it as thin (or thick) as you wanted to by the number of coats you apply.
 
I used a gallon can of carb cleaner, the type with the soaker basket inside, and soaked the pistons one or two at a time for an hour or so, then flush them with clean gas and a little tooth brush action. Took all the crap off them. I would not use phosphoric acid, it'll chew the metal up, if you want to use a mild abrasive us super fine steel wool.

AS long as the pitting is below the wear surface I would not worry about any coatings. Just be sure that the bores measure good and match the piston dimension. I'd polish the pitted areas a little with the steel wool and let them go. I guess it depends on how bad the pitting is. Can you attach a pic ?
 
Here are a few pix. Sorry for the quality. Flash is too bright and no flash is too dark. Well, you get the idea, anyway.
The last pic is the one I hit with the ScotchBrite

AA1.jpg


AA2.jpg


AA3.jpg


AA4.jpg
 
The only part of the piston that carries "weight" is the skirts. If it's near the pin centerline, it isnt riding "on the walls". So I would say ignore the pits. Even on the skirts, as long as there is no debris left in them, some small pits wont hurt you.
 
moper said:
The only part of the piston that carries "weight" is the skirts. If it's near the pin centerline, it isnt riding "on the walls". So I would say ignore the pits. Even on the skirts, as long as there is no debris left in them, some small pits wont hurt you.
Click to expand...
What he said.
 
I wasn't really worried that they would affect anything performance-wise, more like I wanted to clean them up as best I could and wondered about an anti-wear coating. I've noticed most new pistons are coming coated these days. Perhaps there's a product out there that someone's used that thay know will work with no adverse results?
I know the bullet coating I spoke of could stand up to the heat and pressure, after all, we're talking about bullets. And molybdenum is used in many high-pressure/high heat applications. I just don't want to do something that might affect ring/cylinder break-in. So, unless anyone has any proof of something that works, I'll probably leave my experimentation for a Briggs and Stratton.
 
I'd just clean them real well using the carb soaking solution, make sure the ring groove are spotless - polish the pits on the skirts a little with quad 0 steel wool and run them.
 
As for the moly coatings, I would be concerned about the bond with the piston. If these have been run for a while, plenty of oil is baked into the pores of the aluminum, possibly interfering with the adhesion of a coating. You could try it, but I doubt you will notice any difference in performance.

As for the phosphoric acid wash, again it would probably be a waste of time. But then again, if you were going to alodine the pistons...

When I re-use pistons, or other small engine parts, I typically dunk them, make sure the ring lands are free of carbon, and run them through the dishwasher (send wife out shopping).
 
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