Max Piston clearance

[roberto]

I just bought a Montesa Cota 330 and after measurng the bore and the piston I come up with a tolerance of aprox 0.12 MM. Too much?? Should I rebore to the next size or would a new standard size piston be acceptable?? Can anyone help?

[dadof2]

0.12mm sounds slack and I would think a shade over the limit. I would expect clearance when new to be about 0.0025 inch (0.64mm.

The maximum taper or out of round of the bore is 0.05mm. my guess is you need a rebore + os piston.

[fantic303]

Did you measure the piston on the right place (the skirt) ?

[monty_jon]

I just bought a Montesa Cota 330 and after measurng the bore and the piston I come up with a tolerance of aprox 0.12 MM. Too much?? Should I rebore to the next size or would a new standard size piston be acceptable?? Can anyone help?

It depends on the bore size, larger bores 72 85mm have 0.08mm clearance when new.

Also Pistons are not round, they are cam ground and tapered (largest diameter at bottom)

Its best to measure the bore against the manufactures limits, not piston in bore

Edited November 4, 2010 by Monty_Jon

[roberto]

Yes, I measured the piston about an 3/4 of an inch up from the bottom of the piston skirt. There isn

[monty_jon]

Yes, I measured the piston about an 3/4 of an inch up from the bottom of the piston skirt. There isn