Piston Cleaning

So getting round to cleaning the pistons that came out of a WVO engine.. Literally had them sitting in carb dip for the last few months. Stuff still won't come clean.


Recently I got a ultrasonic heated parts washer. Ran two pistons in it for about an hour with mostly water and a splash of Zep cleaner. Have a feeling I may have fubar'd the two. What's your opinion? Left is one that ran through the cleaner, right is one I still need to finish cleaning.. It looks like all the shiny's been cleaned off and now there's mild pitting. I know the Zep can be strong stuff on aluminum.

they'll be blacker the moment you run the engine
get the ring grooves cleaned out (use the rings as a scraper) and leave it at that

What's important is sides of the ring grooves on the side of the piston... that's where the rings do all of their sealing against the piston, and it's very important that that surface is mirror smooth so that it seals against the sides of the rings.

If you dunked just the face of the piston in the ultrasonic cleaner and didn't expose the ring grooves to the Zep you're probably fine, but if the sides of the ring grooves are as chemically etched and pitted as the top of the piston on the left I'd say they are probably paperweights.

Dunno any way you could machine away the pits without making the gaps so wide the rings will slap around.

[486] said:

they'll be blacker the moment you run the engine
get the ring grooves cleaned out (use the rings as a scraper) and leave it at that

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Good enough for me! Any reason as to why they turned gray vs the chrome look? At this point it's just curiosity. Would you modify the way I cleaned them in any way?

It still has some of the same coloring on the sides. I'll upload a pic of it here in a bit. I did have the entire piston submerged. If it is bad I'm not all that worried about it, just don't want to build a potentially exploding engine with it

The rings seal against the wall of the cylinder (of course!) but also against the tops and bottoms of the ring grooves. If the ring-piston groove interface is rough the ring will leak compression and cause excessive blow-by, just like if the ring-cylinder wall interface is rough.




Excessive blow-by *is* a problem in a diesel engine as it can, worst-case, cause a runaway. No way to know how serious the leakage would be in your case... your car your rules of course.

I've overhauled engines before, so I'm fairly aware of how the rings work This however, is the first time reusing pistons in a build. Benifits of working for an engine dealer, always new pistons lol


So here's the side. I'm pretty sure its junk.

By the way... I'm not worried about the top of the pistons at all, I'm still trying to clean the gunk out of the ring lands and haven't bought a ring land cleaning tool yet. If these two pistons are bad I won't lose any sleep over it. I can always get more.

New ALH pistons are not that expensive. I wouldn't use those, pitting from the cleaner is pretty extensive.

turbocharged798 said:

New ALH pistons are not that expensive. I wouldn't use those, pitting from the cleaner is pretty extensive.

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Paper weights they are then, thank you. What type of solution should I use? I read where other people have put ALH pistons in a ultrasonic cleaner but didn't say what liquid they used.

the dark is just a thick oxide layer, just like anodizing

as said, I wouldn't worry one little bit

Nero Morg said:

Paper weights they are then, thank you. What type of solution should I use? I read where other people have put ALH pistons in a ultrasonic cleaner but didn't say what liquid they used.

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I generally use some mexican laundry soap that has TSP in it. Really should find more "con phosphatos" soap as I'm getting pretty low. They don't sell it in the US any more because it promotes algae growth in runoff.

[486] said:

the dark is just a thick oxide layer, just like anodizing

as said, I wouldn't worry one little bit

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That's what I thought it was, if I rubbed it with a clean shop rag it looks like it'd polish off.

Do get some laundry soap that's less an acid but more on the alkaline side?

I guess Ace sells boxes of TSP, so guess where I'm headed to I'll follow up after I run these through the cleaner again. Wouldn't hurt.

I think you'll find the ZEP was not acidic. Most cleaners aren't.

In the side picher the area around the upper groove is shiny. Do these have armored top ring grooves? In other words, a steel insert?

Just the compression ring lands, yeah. These are the first ALH pistons I've ever pulled, is that normal? They're from a 2003 engine.

Ran in the ultrasonic cleaner, 1.3L water, 1.5 teaspoons of TSP, ran for 15 minutes... Main concern areas I have is the pitting that's in the valve recession area, and the ring lands. About to leave the house to get spare pistons, but still curious if these are definitely reusable for a stock engine. By the way... These pistons were in an engine that had a VNT15 (which went bad due to a cracked air box) with .216 nozzles without a tune. This engine smoked like crazy because of it. So damage could be because of my cleaning process... Or because the prior owner was a dork.

Followup, cleaned one piston with just TSP in the machine. Looks brand new, no discoloration. Anyone want a pair of paper weights?? Haha anyways I'm officially not going to to use these old pistons.