So this is not a thread on "should I reuse these pistons" because they are still installed in the block and i'm only doing head work to this thing right now. So the head is going back on and it will get driven till she goes. What I do want to know is what should i do to minimize the increased chance of knock in this cylinder. File down the high spots and send it? This is cylinder 4.

Also there are a few marks in the cylinder wall that are a bit rough. Not much I can do about that I assume. The last time the car was compression checked I believe it was about 130 across the board. Not the greatest but within limits.

I am guessing that at some point in this cars life, or maybe even still to this day, it was ran on a clogged injector because none of the other cylinders show any signs of knock. This cylinder also seemed to have less carbon buildup on the pistons than the rest when I cleaned them. I am putting in larger injectors in so that will eliminate that issue most likely. However, cylinder 2 does have a nice gouge in it that starts somewhat deep at the top of the scratch, and then fades out by mid-top cylinder. Again, I am not rebuilding the bottom end at this time, and I doubt there is much I can do about it, but if anyone has anything I would be glad to know.

This car has been at stock boost on a 16g since my girlfriend bought it. She is just now getting all the issues with it fixed up (that's right, she pulled the head. It's her first big project) This project was to replace the valve seals as it would smoke after idiling for a min. Never while driving though. So I hope the smoke goes away and its not a cylinder issue. Any input is welcome. Thanks guys.

It's probably got ring lands broken.

Ugh. I hope not. The scratching seems to be from where the piston "chips" were deformed and touching the cylinder wall. If you zoom in real close on the bottom photo you can see what im talking about.

I wouldn't doubt you've got broken ring lands. I've been there. The vertical lines are usually a tell tale sign.

brian9397gsx said:

I wouldn't doubt you've got broken ring lands. I've been there. The vertical lines are usually a tell tale sign.

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Wouldn't the car almost for sure smoke while boosting / decel if the ring lands were broken? While driving this thing doesn't smoke a bit. And the compression was not bad in that cylinder.

I am not denying that there is a high chance that the ring lands are screwed, but it just was not showing the signs of it which is weird.

For piece of mind I'd pop the pan and slide it out before I slapped my head on. The last one I broke ring lands on had perfect compression well even around 150.

brian9397gsx said:

For piece of mind I'd pop the pan and slide it out before I slapped my head on. The last one I broke ring lands on had perfect compression well even around 150.

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Even if it does there is nothing that I am going to do about it now. It ran when it came apart so it should run when I put it back together. At least for a while. Its not a daily or anything so if she blows she blows. When she finally lets go I'm just going to build it. Could be 2 days, or 2 years. When we bought the car a few years ago we expected the worst anyway. This thing was a parts car that was picked at and we saved it from certain death .

All I wanted to know was if there was anything I could do to clean that piston up before putting the head back on and what methods I could use.

Just put the head on then. I wouldn’t try to fix the situation.

bastarddsm said:

It's probably got ring lands broken.

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Yeah, I was going to say that, and scrolled down.

jakk220 said:

Even if it does there is nothing that I am going to do about it now. It ran when it came apart so it should run when I put it back together. At least for a while. Its not a daily or anything so if she blows she blows. When she finally lets go I'm just going to build it. Could be 2 days, or 2 years. When we bought the car a few years ago we expected the worst anyway. This thing was a parts car that was picked at and we saved it from certain death .

All I wanted to know was if there was anything I could do to clean that piston up before putting the head back on and what methods I could use.

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Smooth out any sharp points with emery cloth or a dremel tool is the best you can do. It will prevent hot spots on those sharp points.

donniekak said:

Yeah, I was going to say that, and scrolled down.

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I'm just going on hopes and dreams that it's doesn't have any broken. If it does, oh well I guess.

Is it safe to say a bad injector probably caused it? Since all other pistons are fine.

1990TSIAWDTALON said:

Smooth out any sharp points with emery cloth or a dremel tool is the best you can do. It will prevent hot spots on those sharp points.

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Thanks I think that's what I'll do. Just carefully take a Dremel to it.

BE CAREFUL!!!
But those points will be super hot if not addressed.

jakk220 said:

I'm just going on hopes and dreams that it's doesn't have any broken. If it does, oh well I guess.

Is it safe to say a bad injector probably caused it? Since all other pistons are fine.

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I would have the injectors cleaned and flow tested to make sure.

I wouldnt put thAt engine back into service. The area on the piston is damaging the cylinder wall. Its just going to get worse and worse. Is it the reflection of are there several vertical score marks in the wall?

donniekak said:

I would have the injectors cleaned and flow tested to make sure.

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I'm putting on a set of 880 precision injectors I have laying around. These were original injectors .

1990TSIAWDTALON said:

BE CAREFUL!!!
But those points will be super hot if not addressed.

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I hit them with the Dremel. I take some pics in a sec.

amsrn13 said:

I wouldnt put thAt engine back into service. The area on the piston is damaging the cylinder wall. Its just going to get worse and worse. Is it the reflection of are there several vertical score marks in the wall?

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Oh it's going back into service . Im just gonna run it til she's had enough. There is definitely some scoring. Which is I believe from where the knock spots melted outward to the cylinder wall and scratched into it.

When it blows I'll rebuild it.

jakk220 said:

I hit them with the Dremel. I take some pics in a sec.



Oh it's going back into service . Im just gonna run it til she's had enough. There is definitely some scoring. Which is I believe from where the knock spots melted outward to the cylinder wall and scratched into it.

When it blows I'll rebuild it.

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My only concern is that currently that block is rebuildable, you can get away with an overbore if its still in the service limit. Its not a matter of if but when it fails you can only hope you dont destroy the block or put a rod through it. You could bore the block, throw some npr pistons with the 1g rods and have a brand new motor for cheap. If this isnt an option i wish u the best of luck

That motor is already blown, any further and you may have a ventilated block which is hard to rebuild.

amsrn13 said:

My only concern is that currently that block is rebuildable, you can get away with an overbore if its still in the service limit. Its not a matter of if but when it fails you can only hope you dont destroy the block or put a rod through it. You could bore the block, throw some npr pistons with the 1g rods and have a brand new motor for cheap. If this isnt an option i wish u the best of luck

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Nah. When it blows it's getting eagle rods and manley pistons. My tried and true combo. I wish me the best of luck too haha. Thanks.

brian9397gsx said:

That motor is already blown, any further and you may have a ventilated block which is hard to rebuild.

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Believe me, this would not be the first block that I've windowed. I'm fully aware of the consequences. Ive been keeping my eye out for a local 6 bolt block / engine to build.

I missed a running 6 bolt with everything down to the spark plugs wires for $50 on Craigslist by an hour last week. I wasn't happy about that one. I do have a spare compelte 2g 7 bolt that I got for 100. Turbo and all. That was a score.

Knocked down the peaks with a Dremel sanding wheel.

Good luck

My girlfriend changed her mind. We're just going to rebuild it now. It's been a while since I've assembled a bottom end but I think I still got it. I guess we'll see

Lol those scratches aren't from detonation they are from contamination.

That cylinder ate something small, like a turbine blade to chew it up like that. I've seen a nitrous big block hemi eat the tip of a spark plug and the head had damage like that

To be blunt, if the head didn't have identical marks in it you're dealing with an issue that happened a long time ago, because that aluminum head would be destroyed much worse than just the piston

So lick the stamp and send it if it's a daily driver build. High boost though those piston walls are going to have a bunch of blow by though and probably eat a piston ring eventually

chrysler kid said:

Lol those scratches aren't from detonation they are from contamination.

That cylinder ate something small, like a turbine blade to chew it up like that. I've seen a nitrous big block hemi eat the tip of a spark plug and the head had damage like that

To be blunt, if the head didn't have identical marks in it you're dealing with an issue that happened a long time ago, because that aluminum head would be destroyed much worse than just the piston

So lick the stamp and send it if it's a daily driver build. High boost though those piston walls are going to have a bunch of blow by though and probably eat a piston ring eventually

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The machinist I sent my head to said that there were some marks in the head as well but he was able to smooth them out. He did say that he thought it looked like a spark plug tip.

I however, thought that the piston marks looked like detonation marks marks. I never said that detonation caused the scratches directly. What appears to have caused the scratches in the cylinder wall is the bad spots on the top of the piston. Some of them were so close to the edge that some of the peaks went out toward the cylinder wall and were scratching it.

I suppose that a foreign object is possible. But I would think that there would be marks in the center of the piston as well. The marks being only on the edges of the piston usually point towards detonation from what I understand.

I already have the thing tore down so I might as well just build the damn thing. I did not want to do it right now but I also would rather not have it blow right before the shootout. It was more my girlfriends decision than mine because I was just going to put it back together. It was at stock boost on a 16g before and I plan on putting 22psi to it which probably would not have lasted long.