Motorcycle Repair: ct70 piston, piston damage, bill silver

Question
I am learning so be patient. I acquired  a couple of ct70 engines. One has a standard piston and the other has a 1.00mm. I have not measured the piston clearance yet. Should I put a 0.25 oversize in the standard if the clearance is not good? Do you always start out and work up with piston sizes? Does the size affect power and maybe that is why they used a 1.00.Thanks  

Answer
Shirley! Nice to have you back... :>)
Honda makes pistons in 5 sizes.
STD.
.25
.50
.75
1.00

The come from the factory with STD pistons. The .25 increments are fractions of a millimeter, which is about .040" of an inch (1mm).

As engines wear or have piston damage from seizures or whatever, then you have the option of boring the cylinder to the next size that will make a clean straight cylinder again. Heavily worn/seized pistons may require going from STD to .50 to clean up the wear and damage. A machinist has to check the condition of the cylinder, measure the taper, roundness and ridge at the top to determine how much the cylinder needs to be bored to clean it up. If it won't clean up at 1.00mm oversize, then you get to buy a new cylinder and start with STD pistons again.
Pistons don't wear evenly in the cylinders, so you can't just jam a .25 oversized piston in a worn STD bore. There are too many dimensions to consider, as mentioned above.
Boring from STD to 1.00mm on a CT70 wouldn't really have any noticeable effect on power and will probably raise the actual cc size by 1 or 2, at most.

Hope that is relatively clear to you, Shirley...

With aloha,
Bill Silver