Increasing bike engine size

question ; i have a single cylinder motorcycle , 4 stroke , 652 cc and i would like to build it up to around 800 cc , it has bore and stroke of 94mmx94mm or 3.7in x 3.7 in , dont have the option of using a replacement cylinder with a larger bore , so i will have to bore the one i have , i'm looking for sugestions on rod length versus crank throw ??

Welcome to AF.

This question depends entirely on the availability of oversize pistons, oversize cylinders or sleeves (or wall thickness of the existing one), longer stroke cranks etc.

It would be rediculously expensive to engineer your own parts, so buying aftermarket components, if any exist, is your best option.

Unfortunately, since you have not indicated the make/model/year, we cannot help you on locating these parts.

It may be more reasonable to boost the power output of your existing engine.

Here's the two extremes:

You would have to increase either the bore by 5.0mm or the stroke by 21.3mm to get the desired 800cc displacement. Although you can try to get there with a combination of both, that's alot to ask IMO. I think 700cc would be a more reasonable expectation, but I'm not a m/c expert by any stretch.

Check with the bike mfr for options on oversize pistons and go from there.