287cc ring gap ?

[jack82]

Hi fellas........just picked up a big bore piston for my old XL250 motosport.

It was sold to me as a 305 kit but the piston measures 79.5 mm......I work that out to be about 287cc......I'm trying to work out the ring gaps.

Workshop manual has the gaps for the stock motor as,

TOP RING...........0.15 - 0.35 mm

SECOND RING.....0.20 - 0.40 mm

OIL RING............0.20 - 0.40 mm

Any thoughts ??

[DOK]

Over 35yrs since mechanics tech course but general rule of thumb is .002thou per inch of bore equals ring gap.
Quick metric conversion is .002thou = .05mm.
So if the bore is around 3inch then your ring gaps sound about right

DOK