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Cribbs74

Piston to cylinder wall clearance

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Popped the head off of my KT to lap the head and replace the gasket as I had a leak. While in there I grabbed hold of the piston and noticed what I think is excessive movement inside the cylinder. 

I realize that it’s an aluminum piston in an iron sleeve so some play is normal to compensate for expansion, but this seems more than it should be. That said what should it be? 

Thanks,

Ron

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Hi Cribbs, for an air cooled 2T motor around 250cc, you would be looking for a piston bore clearance of around 1.5 thou, measured about 3/4 of the way up the bore near the bottom of the inlet and exhaust skirt. Most of the wear will occur in this area. This is just a rule of thumb guide. Bye, Peter B.

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11 hours ago, Cribbs74 said:

Popped the head off of my KT to lap the head and replace the gasket as I had a leak. While in there I grabbed hold of the piston and noticed what I think is excessive movement inside the cylinder. 

I realize that it’s an aluminum piston in an iron sleeve so some play is normal to compensate for expansion, but this seems more than it should be. That said what should it be? 

Thanks,

Ron

You could call Millenium Technologies and they would know for sure.  They do hundreds of cylinder overhauls a month.  I have no connection myself. Or email them on the web.

Sales/Customer Service

Millennium Technologies/ Revolution Performance

1404 Pilgrim Rd.

Plymouth, WI. 53073

1-888-779-6885  EXT.351

www.mt-llc.com

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17 hours ago, peterb said:

Hi Cribbs, for an air cooled 2T motor around 250cc, you would be looking for a piston bore clearance of around 1.5 thou, measured about 3/4 of the way up the bore near the bottom of the inlet and exhaust skirt. Most of the wear will occur in this area. This is just a rule of thumb guide. Bye, Peter B.

1.5 thou?! Maybe on a freshly bored engine. Some piston manufacturers would recommend more even on a fresh rebore!

Wear limit i would guess would be around 5 give or take

Edited by faussy

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