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newbie piston installation question
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Author:  drtwgn [ Tue Oct 12, 2010 4:10 pm ]
Post subject:  newbie piston installation question

I was installing .040 over pistons, and the third one I did did not want to go in the bore. It turned out that one of the little tabs at the bottom of the piston skirt was somehow hanging up. After a few rounds with a file
(and plenty of cleaning), the piston does go in, but it is a very slightly bit
tighter fitting than the first two pistons feel. It rotates freely in the bore (grabbing the piston head and twisting), so I believe the bores are round.

SO the questions,
how much slack should there be between the skirt and the cylinder wall? I have never seen anything about measuring this.

Is this filed piston safe to use? Has this happened to some of you?

Thanks and Peace

Author:  Fopar [ Tue Oct 12, 2010 4:22 pm ]
Post subject: 

Did you install the pistons by the number stamped on the rod or might have been written on the top of the pistons by the machinist??

Richard

Author:  Doc [ Tue Oct 12, 2010 4:47 pm ]
Post subject: 

.001 to .002 clearance is about right for a cast piston... more for a forged or Hypereutectic (sp) piston.

I would try that piston in a different bore to see if you get a better (looser) fit.

To be honest, a good engine builder (and the factory) measures, sorts and "matches" the pistons with the bores so they end-up with the needed amount of clearance.
DD

Author:  drtwgn [ Wed Oct 13, 2010 8:05 am ]
Post subject:  newbie piston installation question

I am installing based on numberr on connecting rod. I was with the machinist, and we did not test fit pistons before installing on con. rods.
THis is going to be a daily driver, not a racer, if that matters.

all other pistons seem to have just a tiny bit of wiggle in their appropriate cylinders; the one in question has just a tiny bit less. Its more like snug.

Bores are pretty uniform diameter top to bottom, doesnt seem to be a taper, based on measuring the gap in an oil ring placed in the bores.

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