BRIDGE PORT 2 STROKES

[jimg1au]

hi
can some one tell me the hole sizes to drill into the exhurst side of the piston to help cool the motor on a 2 stroke.
cheers
jim

[cyclegod]

I always drilled 0.9mm and it seemed to work O.K

[Freakshow]

No need to drill holes unless its on a bridge, then maybe one, and size wont be an issue so longs as its smaller then the bridge width thats covering it, try one of the bits you use for pop rivetts the stumpy ones

but you should only need to put drill tip dimples down both side of the piston either side of the ex hole to hold some oil to bring up with it from the charge.  i drill 4 dimples down both side, soime time if im in the mood nd feeling a bit crazy i drill them all over the place, be the funniest piston someone would see if they pulled it out . hehehe.  but then again never seized a piston on the hot side ever, even on the superlight racer thats 13,000 or more revs on a 100cc air cooled so it must of  worked

[Lozza]

Depends on the width of the bridge but a 3mm bridge I would give it 2 X 2.5mm holes, be sure to chamfer the holes after you have finished drilling. The bit of green paper with any late Wiseco will explain the process.

[jimg1au]

thanks lozza
its for a cz400 which have large bridge port like the cr250 elsinore.the std cz piston has 1 small hole but i knew you told me somthing else when you had my cr barrel.
cheers
jim