125-200cc Diy 165 ???

hello everyone ,

firstly I'd like to apologize as I'm sure that this is a question that has been asked a million times and that generally the question would be answered by Pm-ing wallybean (but my pm's don't work for some reason grrr).

so just a bit of background on my bike first , I bought the bike (wre 125) as a total wreck back in September of last year for a steal! £500 , the bike had no wiring of any kind , and had been sat outside for a few years uncovered. pretty much everything has been changed , including the engine, to bring the bike up to cr/wr spec . i also bought a lighting loom for the cr , however still the stator that came with the bike was toasted , not surprisingly given the overall state of the bike so I also added a pvl 650 fire programmable ignition as a few of the members in the cafe seemed to have fitted pvl's with great success (and this one has the added benefit of lighting) .

now , due to the scarcity of these bikes in the uk , a conventional 144 kit is IMPOSSIBLE to come by with the exception of some *achem* dubious looking cylinders from a source on eBay from Poland.

my question is this , if overbored to 62mm , with the head correctly volumed and modified to fit the larger cylinder diameter , what is done to the power valves? are they merelycut down to fit the new bore? , is there any porting wizardry to be done , i.e. exhaust port widened/ raised , or transfer port work?

i would just like to add that if a 165 is too ambitious/ more difficult to a measurable degree I would be more than happy with a 144 sized overbore. and the engine is a 2012 which I think affects some pf the work

thanks in advance

YES ! my pm's are fixed !!

thank you kind moderator

Without doing some cylinder welding the newer cylinders are limited to a 58 mm bore(144). Any over bore will require you to re-machine the power valves. They really need to be both cut to fit the new bore but also the bottom edge needs to be raised as when you machine it back to fit the bore it lowers the edge. If you don't remachine the bottom edge to original spec you will lose bottom/mid performance. Both of those things are more extensive when boring to 62 mm.

Nothing is impossible but some things are more difficult and depend on your skill set and availability to a machine shop.