Piston damage, Is this piston toast? Options

[Phoenix914]

Happy New Year!

I just cleaned up the pistons for my rebuild and found some pitting on one of them after all the carbon was removed.









This piston was at #1 cylinder. Is it unusable? I'm certain they are NPR 96mm pistons from a late-80's rebuild.

I already bought new rings!

Any opinions would be appreciated.

[Superhawk996]

Its gone.

That piston appears to be victim of detonation. May have been running too high of compression ratio.

Time to move on. Carefully check compression ratio on the rebuild.

[bbrock]

Its gone.

That piston appears to be victim of detonation. May have been running too high of compression ratio.

Time to move on. Carefully check compression ratio on the rebuild.

Care to elaborate on the diagnosis? I've seen folks post pics of pistons nicked by dropped seats that others said were good to run. Curious what makes this damage different. I'm not challenging the opinion. Just hoping to learn a little something. (IMG:style_emoticons/default/beerchug.gif)

[Superhawk996]

Care to elaborate on the diagnosis? I've seen folks post pics of pistons nicked by dropped seats that others said were good to run. Curious what makes this damage different. I'm not challenging the opinion. Just hoping to learn a little something. (IMG:style_emoticons/default/beerchug.gif)

@bbrock

The irregular round pits that look like craters from mini localized explosions are what I'm keying off of. Not consistent with foreign body damage.

Also if you look at the edge of the piston you can see it is beginning to erode away consistent with detonation and localized overheating. You'll also see the small craters forming around the tangent to the piston dome in a place where foreign objects would be hard to occur.

I'm a chassis engineer by trade but I've been around more than a few dyno teardowns of race engines in my career and what I've seen labeled there as detonation looks to be similar to my eye. I'd certainly defer to someone like Jake though or a real powertrain engineer.

Personally, I'd never run a piston damaged like that. The sharp cratered and eroded edges that wrap around the piston dome will always present the opportunity for localized hot spotting that just encourages detonation to start. No way to fill them in or smooth them to my satisfaction.

Could you . . . . sure, if I had no $$ and no other alternative and IF you backed the CR down it would certainly run for a while. The problem is would I go to all the time and effort to rebuild, only to put a damaged piston back in? For me, no way.

If I was going to reuse, I would 1st check the skirt diameters to see if there is any evidence of collaspe. Collapse skirst would be a no-go. If the skirts checked out, I'd then do dye penetrant on the piston ring lands just to make sure there is no cracking there. Then I'd have to try to eliminate any of the shap edges around the crater rims, and then try to do something to smooth that damage at the dome edge. All of this is way too much work in my opinion to end up with . . . a piston that is still damaged. I've never understood the desire to reuse damaged pistons as you allude to, though I've certainly seen people do it. Personally, I don't get it and not worth the risk to me unless it's the difference between driving and walking. I've been there too but would still try to find at least a better used piston.

I'm currently stuggling with this right now on my 2.4L pistons from the six. Recall the valves met the pistons. The ethical question in my mind -- should I offer them up for sale cheap over on the Bird with full disclosure (and witness marks that pistons hit valves)? I personally would not reuse them but maybe someone in a pickle might want to? (IMG:style_emoticons/default/idea.gif) I haven't made up my mind - not sure I want to offer something to someone that I wouldn't personally reuse unless I was in a bind.

That logic was at the core of my assessment here. Would I resuse it? No I wouldn't, and that is where my answer came from.

[mepstein]

Care to elaborate on the diagnosis? I've seen folks post pics of pistons nicked by dropped seats that others said were good to run. Curious what makes this damage different. I'm not challenging the opinion. Just hoping to learn a little something. (IMG:style_emoticons/default/beerchug.gif)

@bbrock

The irregular round pits that look like craters from mini localized explosions are what I'm keying off of. Not consistent with foreign body damage.

Also if you look at the edge of the piston you can see it is beginning to erode away consistent with detonation and localized overheating. You'll also see the small craters forming around the tangent to the piston dome in a place where foreign objects would be hard to occur.

I'm a chassis engineer by trade but I've been around more than a few dyno teardowns of race engines in my career and what I've seen labeled there as detonation looks to be similar to my eye. I'd certainly defer to someone like Jake though or a real powertrain engineer.

Personally, I'd never run a piston damaged like that. The sharp cratered and eroded edges that wrap around the piston dome will always present the opportunity for localized hot spotting that just encourages detonation to start. No way to fill them in or smooth them to my satisfaction.

Could you . . . . sure, if I had no $$ and no other alternative and IF you backed the CR down it would certainly run for a while. The problem is would I go to all the time and effort to rebuild, only to put a damaged piston back in? For me, no way.

If I was going to reuse, I would 1st check the skirt diameters to see if there is any evidence of collaspe. Collapse skirst would be a no-go. If the skirts checked out, I'd then do dye penetrant on the piston ring lands just to make sure there is no cracking there. Then I'd have to try to eliminate any of the shap edges around the crater rims, and then try to do something to smooth that damage at the dome edge. All of this is way too much work in my opinion to end up with . . . a piston that is still damaged. I've never understood the desire to reuse damaged pistons as you allude to, though I've certainly seen people do it. Personally, I don't get it and not worth the risk to me unless it's the difference between driving and walking. I've been there too but would still try to find at least a better used piston.

I'm currently stuggling with this right now on my 2.4L pistons from the six. Recall the valves met the pistons. The ethical question in my mind -- should I offer them up for sale cheap over on the Bird with full disclosure (and witness marks that pistons hit valves)? I personally would not reuse them but maybe someone in a pickle might want to? (IMG:style_emoticons/default/idea.gif) I haven't made up my mind - not sure I want to offer something to someone that I wouldn't personally reuse unless I was in a bind.

That logic was at the core of my assessment here. Would I resuse it? No I wouldn't, and that is where my answer came from.

Yes. sell them cheap. People use engine parts for all kinds of projects or mock ups. It might not be worth the effort to pack and ship but that's up to you.

But I agree with the idea that you never want to use below par parts for an engine build unless it's just practice.