WallaceMcGlynn
CB750 Member
My cb has been bored out to 64.97mm. Ring broke in cylinder four. There is some scoring in the cylinder. I will need to have the cylinder machined out. Any one know what the allowable limit might be?
First we need to know what bike you have. I'll move your post to the appropriate spot after I know the year, you should get more reponses then. Either way you have to bore all 4 cylinders if one is damaged, you will make the engine out of balance if you only put one oversize piston in the engine.
We were just discussing 65.5 bores a short while back, but if you got damage at what is basically a 65 mm. bore you may well have a problem as the 65.5 is only 10 thousandths more to a side and will likely not clear up much if any damage there.
X2 the upper comment, you don't just bore one cylinder by itself.
yes 65.5 is as big as you can go. Your cylinder looks terrible though by the picture. I would look for a used one on ebay and bore it to what ever piston kit you decide to go with.
You will still have to take the cylinder to a machine shop to replace the sleeves then they will have to be finish bored to your pistons. So you will have sleeve removal and replacement labor plus the final bore price plus the price of the sleeves.Cheaper to just get a used stock cylinder then have it bored...you wont be paying for the sleeve replacement. Guess I dont really know what you are trying to accomplish with this motor...racing, street riding?