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Piston Scuffing


Parkertii

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How much "scuffing" is acceptable for a set of pistons? as long as they still measure to the correct spec are they ok? or should they be replaced if they have a decent amount of scuffing present. 

1972 2002tii- Cannibalized

1985 318i- Retired

1974 2002tii- daily driver (summer)

1999 323 e46- daily driver (winter)

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Without looking at them and measuring them we can't tell you if they are usable. If the pistons are scuffed what do the bores look like? Take them to a machine shop and ask them, you need to measure them very carefully piston skirts are not round they are slightly oblong and there is a very specific point you need to measure. Basic rule to start is if you can feel a grove with your fingernail it is too deep. How many miles are on the pistons and the bores?

1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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the bores are just fine, the pistons came out of a different engine. The reason that i am thinking of using these pistons is because im an idiot, In being a idiot i dropped one of the pistons that i was originally going too use while fixing a previous mistake. Another board member generously provided me with a set of pistons that might be able to be used, but being used they do have some scuffs. Im not trying to be picky but i want to make sure that they are still in good enough shape to use as i dont want to have to pull the motor and rebuild it again in the near future. i'll measure them and make sure to post a picture as well once they are cleaned up tomorrow!

1972 2002tii- Cannibalized

1985 318i- Retired

1974 2002tii- daily driver (summer)

1999 323 e46- daily driver (winter)

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I don't use them if there is scuffing that obliterates the barrel marks. (circumferential grooves around the piston)

 

That's really conservative, I know, but I live under this delusion that I'll never open up the engine again, so the pistons

should be 'as- new'.

 

Also measure the ring grooves- sometimes they really wear like crazy...

 

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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Along the lines of Toby B's post--I'd be much more concerned about ring land (groove) wear than minor/moderate scuffing.  Presuming you're using new rings, I'd check each land with a new ring (insert the ring backwards into its appropriate land and use a feeler gauge to see how much clearance there is between ring and land--check the shop manual for specs.  Sloppy lands will allow the ring to wobble in its land, further enlarging the land until the ring breaks.  

 

mike

'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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