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Old 03-04-2012, 02:22 PM   #1
Join Date: Sep 2011
Location: San Diego
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M10 Piston Ring questions

I have a 1985 318i with an engine that needs rebuilding. It will be my first time doing this, and i have a question on piston rings. Ive looked on some sites for a piston ring set and i keep seeing them standard, .25 over, and .5 over. it makes enough sense, but do you only use those when you get oversized pistons right? I plan on rehoning the cylinders, would i use the standard size?
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Old 03-07-2012, 05:06 PM   #2
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Location: NSW, Aus
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It depends on the wear that the pistons have already. If they are heavily worn, then rehone and then measure the new bore diameter. This new diameter will tell you what ring size to put on.
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Old 04-15-2012, 06:51 PM   #3
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If they are heavily worn, then rehone
If they are heavily worn, then rebore and buy new pistons. They'll come with rings...

If the cylinders are good (not unusual) you hone and use standard pistons.
If the PISTONS are good (unusual) you buy new ones, and they come with rings.
Evaluating the pistons is a bit involved- you need to measure the skirt accurately,
check the ring gaps, the wrist pin bosses, yadda yadda.
I've torn apart a bunch of M10's, and the skirts are usually worn too much to justify
reusing them.


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Old 04-16-2012, 09:15 PM   #4
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Location: The 209
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Rebuild with this kit, Please?
2.6L M10 Stroker
Ok, I know it's expensive as all hell, but this would be pretty rad
85' 318i ~The Bronze Bomber (FrankenM10 with a Forced Future )
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