rg250 piston and rm125 upgrade compatibility questions

[twinrock]

i have been riding my latest lil stroker around, rg250 which im digging alot.. its the early non powervalve ...its actually pretty good lil thing feels just like an lc..only lighter...how ever...
as usual you cant have too much of a good thing so i was lookin at up grades..now i know i could just put a rz engine in there..i have the mounting kit and a good bottom end already..
but i went to the local dirt bike wreckers and compared a spare rg cylinder to a rm125 84/85 cylinder..man they are pretty close and with not much work would fit on...transfers were much bigger as were reed cage and extra ports...the major difference being that the rm cylinder was taller by about 5mm..
maybe pistons could mixed and match or skim the bottom of the rm cylinder?? the rm 125 is rated at 40hpr and the rg 250 at 45!!! maybe im getting too complicated lol...reguardless i do intend to rebuild the rg in the not too distant future and and having trouble finding may piston options..im told gt250/x7 pistons fit...anyone confirm this ? any ideas or thoughts are welcome thanks

[EEKNOWS]

No RM125 was ever rated at 40HP. Put 5mm longer rods in and no need to machine cyclinders.

[Heretic]

i agree, i had a few rg250's, they were a nice little bike, good fun. i reckon the way to go is to look for the later 250 exhaust valve (gamma) engine, it would slot straight in, there was definatley a difference with the no powervalve one

if you did go another piston you'd have to match it spot on, not only bore, wrist pin diameter, but also height from wrist pin to crown and ring end location, as well as piston skirt depth. i looked into it when i had my rg500. the piston really is the valve and any diference will throw out the port timing maybe only by a few degrees but that could fuk the whole thing up, especially with no exhaust valve

the RM125 barrels i think would have been designed for a lower rev powerband range and punch too i think than the RG, a look at the pipe would confirm that, it probably would run worse. you'd have to get custom pipes, cdi unit blah, blah, blah

try the NZ wreckers

or water injection into the exhausts maybe, that would be pretty neat with braided lines, especially for a semi naked bike.