Cafebuilder
Its not a Cafe without Clubmans
Whats the difference between a 10 over and 20 over sorry if this doesn't make sense Im somewhat new to pistons.
Piston sizes?
- Thread starter Cafebuilder
- Start date
Cafebuilder
Its not a Cafe without Clubmans
Thanks also do you or someone else know the standard piston size to a 1970 CB350 and would the 20 over improve the performance of the bike also would I have to bore it out?
rockcitycafe
I make things.
the standard size is in the service manual, you can find one online for free if you search, if you can't, message me, I can dig through my laptop and find mine in pdf. and no, .020" over won't improve the performance, it's like a .01% difference in displacement, the idea of oversize pistons is so that the bike can be serviced without throwing away the cylinder block (these bikes were made in a time where things weren't just thrown out). .010" or .25mm over is considered first over, .020, second, etc. first over is sized so that a new piston and rings can be fit into a freshly honed (not flex hone, a real hone, done by someone who has experience and a real bore gauge) cylinder to restore compression and oil sealing to stock when the cylinder and rings have become worn to the point of causing poor performance and oil use
Cafebuilder
Its not a Cafe without Clubmans
Thanks much appreciated and if I cant find a manual I'll let you know 
The Jed
Been Around the Block
To expand a little on what rock city had to say, it sounds like you're looking for a big bore option? Big bores come in multiple mm rather than fractions of a mm. For instance with my bike (gs 1100) I can get big bore kits in 1 mm increments up until I reach just under 1200 cc which is 4 mm over stock. Anything more than that and the block needs to be re-sleeved and the crankcase bored as well. The real benefit though comes from higher compression pistons, which most big bore kits come with. Pair that big bore and higher compression with the right cam(s) and BAM! completely different bike that will have you grinning at what you have created. And the money pit just keeps going from there....
