Does the "First Oversize Piston" mean you have to bore the cylinder?

 

Hey All!

When buying a piston, does "first oversize" mean that the cylinder has
to be bored out a bit to fit or is the piston just a slight bit larger
than the original that it'll fit after other pistons have taken their
toll on the cylinder walls?  (I hope that made sense..)

Thanks!!!

Scott

 


For sleeved cylinders, you will need to have your cylinder bored to
the exact diameter of the new piston, so, you should first hand buy
the piston and send it along with the cylinder for a engine shop to
bore to exact match.

Plated cylinders found on some better bikes are slightly different,
but anyway, if it's an oversize piston, the cylinder will have to be
bored out and re-plated.

Not sure if you're talking about the letters along with piston (A, B,
C...) that designates very tiny diameter increases. These are for
plated cylinders and you match your cylinder to a letter... When my
plated cylinder two stroke ran (eons ago), I used the piston that was
available, never had a problem...

hth

-- T

 

hone:
    polishing stones lightly remove surface scratches
    inside diameter of cylinder remains close to the same
    (normally no over bore piston required)
bore:
    big strange looking drill bit in fixture drills a new
    slightly larger hole than original hole...
    (1 over 2 over..ect....) requires larger piston
    many cylinders have a special anti scratch
    slippery coating on them... when you drill thru
    this coating it will need to be redone...

regarding piston clearances....here's
some info from back when I messed
around with modding jetski's
http://web.archive.org/web/19990220035008/www.groupk.com/seizures.html

 

"john"  wrote:



jetski'shttp://web.archive.org/web/19990220035008/www.groupk.com/seizures.html


Thanks, John. That was an interesting read.
How do I pressure test my GasGas?

220...
230...
240...
BOOM!!!

I'd say about 245.

 

pressurize the case 4-6 psi
if pressure drops you have a leak
you douse the gasket areas with
wd40(is there anything that stuff can't do?)
and the leak will bubble up the wonder
lube into a bubble bath spot letting you know where
you messed up...

pressure test & compression test are two different birds.