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Request opinion on bore scratches and piston defect
Hi everyone, I'm in the midst of rebuilding a 05 LM7 5.3L and found some scratches in the bore on cyl #1, along with scratches on the #1 piston ring lands. I also found one piston has a casting flaw on the top, basically a divot about 1 mm diameter. Please see pics below.
The end goal for this motor is a SBE turbo setup in a Silverado, 600 hp or so. I am trying to avoid taking it to the machine shop, but I am replacing all of the bearing, doing a DIY ball hone and putting in new rings. The bore scratches don't worry me much since I'm honing it, but the casting flaw in one and the scratches in the other piston have me looking for some advice. I'm pretty sure I can get a couple of stock 5.3 rod and piston assemblies for cheap, would you all swap them out? Or just put what I've got back together and call it good? Thanks!
The top of the piston is really rough. If you wanna run what you got, you might consider replacing just the 1 piston. It would be a shame to have it come apart under boost and tear things up.
The Bore is not going to clean up much with a hone. It will take the sharp high spots off though.
You will probably use some oil in that cylinder and have some blow by also.
That place on the piston never touches the bore. Furthermore, it's below the top ring, and above the 2nd. The damage probably was put there while building it. The scratches in the bore also all go up higher than the mark on the piston, some of them higher than the top ring. The 2 things aren't related.
Looks to me like in addition to whatever scored the piston, either something in the motor blew up at one time and shed metal into that cyl, like maybe a valve problem; or, just some yerbasic dirt or sand got in there; or, some metal chips or something got left in there when it was built. I agree with Brick, looks pretty deep, I doubt it will hone out.
I did end up replacing the block, found another one on FB marketplace for $40. At that price it was a no-brainer. I also bought a used piston and rod assembly off eBay to replace the one that has a casting flaw.
05-30-2023, 02:07 PM
Request opinion on bore scratches and piston defect 
