Scratched piston skirts?

G

getblown5.9

Ceritified Kleenex Dealer
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Aug 3, 2006
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I have a set of 6 stock pistons out of a stock SO 24v with over 100k miles that I was planning to use for next year after some reworking.

I was cleaning them up and noticed a few of them have some scratches down on the skirt. they are minor, and not deep, you can barely feel them with a fingernail. The old rings all looked good, the top of the pistons are all good, its just some scratches on the skirt. What would have caused this without damaging anything else, and are they OK to re-use since the skirt should be touching the walls anyway?

Im planning to fly cut them and open the bowl, and possibly coat them. But if its too risky I'll have to see about getting a set of new stockers and having them worked.
 
It can happen from getting something in the cylinder while it was running, like dirt ect, or lack of lubrication. Or they could have been scratched on removal from the carbon not being cleaned off at the top of the cylinder.

Try to buff them out, but those horizontal groves hold the oil on the skirt, and that is what the piston floats on going up and down the cylinder. If its bad enough you can get piston slap, but if they are really minor its not such a big deal.
 
This is the worst one, looks worse than it is because there is carbon down in the grooves, but you can barely feel it.

165714.jpg
 
Next time don't take a picture of your boxers. :badidea:

That does not look bad at all, if it barely catches a nail hit it with a little emery cloth and smooth it out.
 
Bore was too tight for the heat/stress seen. need more PTW and coating would have reduced that effect drastically.

Pistons will grow from pressure/heat and egg shape in that area, if it goes too much further it will sieze in the bore, then it gets expensive
 
Piston might be out off round from excessive heat... bore out of round...or even worn crank or rod bearings can all cause that...

Could be a sign of a timebomb...
 
FYI, these are not from my engine, i picked them up from the classifieds. Was told they were out of a stock motor with over 100k on them. I plan to have them flycut, bowl opened and if it will help, I'll go ahead and have them coated ceramic on top, teflon on the skirts.

As far as I know my motor/block is still good and wont require any boring, should only need a hone and ready for re-assembly. Since this is a pulling only engine build, should the PTW clearances be left a little loose? If so how is this done without boring the block to open the bore size slightly?
 
06 DIESEL said:
Next time don't take a picture of your boxers. :badidea:

That does not look bad at all, if it barely catches a nail hit it with a little emery cloth and smooth it out.
Click to expand...

LOL there was a bag of old clothes to be thrown out, I saw it and thought they'd make good shop rags. I just never cut them up, and of course the first piece I grabbed from the bag is a pair of under britches. there were no stains on them when i started thank goodness....but they are a little black with carbon now from cleaning the piston.
 
getblown5.9 said:
FYI, these are not from my engine, i picked them up from the classifieds. Was told they were out of a stock motor with over 100k on them. I plan to have them flycut, bowl opened and if it will help, I'll go ahead and have them coated ceramic on top, teflon on the skirts.

As far as I know my motor/block is still good and wont require any boring, should only need a hone and ready for re-assembly. Since this is a pulling only engine build, should the PTW clearances be left a little loose? If so how is this done without boring the block to open the bore size slightly?
Click to expand...

You can hone a extra thou or so with no issue. but make sure the machine shop does it and not you with a drill motor.....:lolly:
 
Yea, machine will be doing it. I've never built any motor before, so this is all new to me. Machine shop will handle all the tight tolerance stuff, and then I'll have a knowledgable person helping me actually assemble everything once its back from the machine shop.
 
id be leary of using those/that piston TJ, if it were a couple of small scratches then i would say use it, but that looks like a good scrape, though not deep, still none the less, it is fairly wide on the piston skirt. if it were going in a stock HP/rpm engine i wouldn't hesistate, but your engine is going to be under a bit more stress, better safe than sorry.

Wes
 
I have to agree with these other guys TJ, i reused my same pistons but they sure didnt look like that. The money you spent on just Kenny's girdle could have went for some good pistons. I would cal snedge about some new ones.
 
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