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Is a scratch on a piston head okay?

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Old 06-19-2017, 10:10 PM
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dreygata
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Default Is a scratch on a piston head okay?

I'm in the process of rebuilding my engine, and I figured I'd clean the engine while it's out.
Pulled the pistons and they are black with carbon, nothing unexpected. After soaking the #1 piston head in some aluminum safe simple green, occasionally brushing it with a well worn toothbrush and wiping it with a paper towel, I noticed this:



There's a scratch line from the center going outwards and an aberration below the "+" mark.

Are these things I should be worried about? The other piston are pretty flawless and had I not cleaned off the carbon I wouldn't have known.
For the record, I'm doing an engine rebuild because of a shredded #1 rod bearing.
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Old 06-20-2017, 01:36 PM
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V2Rocket
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smooth it down if you can but dont worry too much.
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Old 06-21-2017, 02:04 PM
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GPA951s
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No worries, You should have seen the pistons in my First Car! They had pretty deep impressions from where some previous owner lost the timing belt.... They made their own valve reliefs! Ran Fine... Took a grinder to smooth them out..
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Old 06-21-2017, 11:17 PM
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That's a sigh of relief! I'll likely leave it as it is since they are pretty shallow and smooth as it is.
I nearly have the tops carbon free after soaking most of the week.

Should I bother cleaning the rest of the piston? I don't think the piston skirt or the under side of the piston where it connects to the connecting rod would benefit from cleaning.
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Old 06-22-2017, 01:59 PM
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They get Dirty pretty Quick, The Most important is to get any crap out of the ring groove so they are Free..and there is no Debris in the Grooves... And Remember,, DONT mess with bores, Dont even scotch brite or anything.. Wipe them out with a cloth and call it a day.... Touch those bores with anything else and a little project just turned into a big project... Ask me hoe I know...
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Old 06-24-2017, 10:53 AM
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michaelmount123
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Originally Posted by GPA951s View Post
They get Dirty pretty Quick, The Most important is to get any crap out of the ring groove so they are Free..and there is no Debris in the Grooves... And Remember,, DONT mess with bores, Dont even scotch brite or anything.. Wipe them out with a cloth and call it a day.... Touch those bores with anything else and a little project just turned into a big project... Ask me hoe I know...
Do be careful if you go into the ring grooves! The rings need a very precise machined ring groove surface to seal against, and those sealing surfaces are easily damaged with a tool of any sort. Your soaking likely has them plenty clean.
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Old 06-24-2017, 10:56 AM
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The rings are pretty free already. Most of my soaking has been focused on the top surface but i know the ring grooves got cleaned up some.
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Old 08-03-2017, 10:04 AM
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I managed to get my hands on an ultrasonic cleaner, and put the piston heads into that for a while, so the grooves look great!
I'll keep the advice in mind about the bores GPA951s. The most I've ever been told is to wipe is out with incredibly fine sandpaper (greater than 600). The ONLY reason I've considered that is because the mechanic has been working on Porsche's his entire life and owns a classic car shop.
I'll likely install then as is, then if compression sucks, consider honing or whatever, as it's easier to start that way than the reverse.
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Old 08-03-2017, 12:07 PM
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Don't touch the cylinder walls, at all, unless you're using the Sunnen paste-hone.

Clean them with a soft cloth to get any **** off, and oil them for the new pistons/rings to go in.
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Old 08-03-2017, 12:17 PM
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Originally Posted by V2Rocket View Post
Don't touch the cylinder walls, at all, unless you're using the Sunnen paste-hone.

Clean them with a soft cloth to get any **** off, and oil them for the new pistons/rings to go in.
Cool thanks. I'm going to try to get them in this weekend if I have the time. For oiling, do you just put a layer of oil on the rings prior to pushing them in with a piston rings compressor? I've been cleaning the block so it looks presentable. Just need to go over the head gasket surface with some permatex gasket remover .
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Old 08-03-2017, 02:13 PM
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Well when I was a newbie at the Alu-sil Game I "Scuffed" up the Cyls with 1500 Grit paper and lots of WD-40, End Result= Engine lasted 1000 Miles before the Cyls ate themselves... Wipe them out with a clean cloth and call it a day, And don't take my word for it call Mike at Lindsey Racing.. Trust me, Learning the hard way is no fun...
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