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My 750-4 pistons were well covered with carbon when I tore the engine apart. I cleaned them up and they look pretty good.

However, while the new compression rings fit, they fit a bit tightly (they are the right rings), and the clearance seems minimal (a little smaller then it should be). I had cleaned the ring lands with a broken ring (cheap approach but usually works), but I can still see a lot of what looks like carbon/varnish on the flats inside the lands, which I can't seem to scrape out with the broken ring (and I don't want to grind around in there with it!).

Is there a solvent of some kind that will clean the lands out well, that is safe on aluminum?
 

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AZ's Official Mechanic
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could try soaking in B-12 chemtool (you can get a gallon at autozone/checkers or a small can at walmart) then a BRASS wire brush to scrub them
 

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can i ask a question ,did you happen to get aftermarket rings like wiseco or someting, i was reading up on this before i rebuilt my mojave ,and what they said if you have a stock oe piston and use wiseco rings they will not seat correctly on the lands ,due to the wiseco are thicker than oe rings.you have to use oe rings on oe pistons i guess,

as for cleanin the pistons take em to a machine shop and hot tank em, iv done this for all the engines i re ringed they come out lookin like brand new:)
 

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Obfuscation Engineer
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can i ask a question ,did you happen to get aftermarket rings like wiseco or someting, i was reading up on this before i rebuilt my mojave ,and what they said if you have a stock oe piston and use wiseco rings they will not seat correctly on the lands ,due to the wiseco are thicker than oe rings.you have to use oe rings on oe pistons i guess
as for cleanin the pistons take em to a machine shop and hot tank em, iv done this for all the engines i re ringed they come out lookin like brand new:)
Ummm , not wanting to over do my Richard Cranium impression but wtf are you thinking ? Long before the carbon dissolves the Aluminum piston will have liquefied in the caustic soda solution .

Mechanical cleaning is all I have found that will remove carbon from aluminum . Although ring groves will get larger with use the rings will rarely get much thinner . Verify any suspicion that the new rings are indeed thicker by measurement . If it is only a slight difference wrap a length of heavy cotton string 1 1/4 to twice the way around a groove and cover the string in fine valve grinding compound with a little grease and use a see saw motion alternately pulling with either hand . Change positions often and inspect often to see if the deposits are going away and if ring fit has improved . If the difference in ring thickness between new and old is much more than .003" something else is wrong .

~kop
 

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well i take em to machine shop and they clean em up might not be hot tank per say but what ever they use it cleans em well, that is what i meant. i don't have time to clean them mechanically most of the time,so i give em to my machine shop and they clean them.
 

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Obfuscation Engineer
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METHYLENE CHLORIDE; dichloromethane; methylene dichloride
CRESYLIC ACID; cresol; hydroxytoluene
XYLENOLS; dimethylphenol blend
PHENOL; carbolic acid

industry name is "Zepresto" and NOT something you want to keep around the home .

~kop
 

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itching to ride
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My uncle would use a broken ring to clean the groves of carbon on his automobile projects. I just drop them in the chemtool can and let them soak. A lot less scraping.
 
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