Regular readers of bigtwins.org, our "mother" site, should be aware that there is a limit to easy size increases for the 920 at 96mm (about 1000cc). This is due to a couple of factors, the most major of which is the outside diameter of the stock cylinder sleeve at 99mm. Due to this and the "fire ring" style head gasket area we are constrained from boring past 96mm - there just isn't enough "meat" to accomodate a wider bore. Even this size makes me a little nervous as sometimes parts of the fire ring get machined away at this figure. I would refuse to sell 96.5mm pistons. The first generation bikes used the engine as a stressed member of the frame, meaning that part of the bike's weight is held up by the engine studs and the cylinder sleeves. I see a millimeter and a half as an absolute minimum thickness. Also, due to the shape of the 920 sleeves (they have a ridge part way down their outside) it is not practicable to sleeve them out. Plus the aperatures in the cases is 99mm, so there is no room anyhow.


So what can be done? This.