Does the "First Oversize Piston" mean you have to bore the cylinder?
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From: kxdude4 on 25 Feb 2010 19:07 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
From: Tiago on 26 Feb 2010 04:13 On Feb 25, 9:07 pm, kxdude4 <nos...(a)my.net> wrote: > 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
From: john on 26 Feb 2010 09:16 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" <nospam(a)my.net> wrote in message news:9t3eo5p3t6ug5snr1tsg87fna5imasjkb3(a)4ax.com... > 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
From: Wudsracer on 26 Feb 2010 11:25 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 *************************************************************** >On Thu, 25 Feb 2010 16:07:29 -0800, kxdude4 wrote: >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 **************************************************************** Wudsracer/Jim Cook Smackover Racing '06 Gas Gas DE300 '82 Husqvarna XC250 Team LAGNAF
From: Dean H on 26 Feb 2010 12:34
"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. |