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

[kxdude4]

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

[Tiago]

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

[john]

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

"kxdude4" <nos...@my.net> wrote in message
news:9t3eo5p3t6ug5snr1...@4ax.com...

[Wudsracer]

The easiest way to get a good answer to your question is to check the
chart for piston sizes.

If the "first oversize" piston is 1/4 mm, then it will require a
cylinder bore, or bore and re-coat of the bore to accommodate the
piston.
If the "first oversize" piston is .01mm, then it is like the B, C, & D
oversize pistons that companies such as GasGas use. These pistons are
"oversized" very slightly, to help the piston run true in the bore,
and all sizes use the exact same specification rings. No boring
required.

FYI:
Kawasaki dirt bikes have been using a nikasil type bore coating since
the early 1980s. (At least, the '83 KX125 that I set up and
maintained for my son, Josh, had a nikasil cylinder bore coating.

Good Riding and Wrenching!

Jim

***************************************************************

****************************************************************

Wudsracer/Jim Cook
Smackover Racing
'06 Gas Gas DE300
'82 Husqvarna XC250
Team LAGNAF

[Dean H]

"john" wrote:

> regarding piston clearances....here's
> some info from back when I messed
> around with modding 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.

[john]

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.

"Dean H" <dfh...@optonline.net> wrote in message
news:bc6de1a4-d715-407b...@g26g2000yqn.googlegroups.com...

[kxdude4]