Bore dia. When to go bigger?

[zixxerboy]

Have my 76 340 as apart as it gets and it needs new pistons. Now would be the time to get it bored out to the next size if required.

I want to drop the jugs at a machine shop to get an accurate measuremnet. Then I need stock I.D. and the allowable tolerance. Anyone have that info or able to point me to a source?

Thanks

[magnumforce]

Howdy Zix, I don't know if this info will help but here's a c/p from S.P.I. pistons and Hi-Perf engineering. I think it should be close to what the orig. were ( I hope) Yours would be a 64mm bore...
Quite a few just use this for referance with good results.

Measure the cylinder for clearances and out of roundness, service limit is .0035" out of round up to
65mm / .0045" out of round over 66mm larger size.
Cast iron cylinders- finish cylinders with a 220 or 300 grit stone
nikasil or electrofusion cylinders - if necessary can use a 500 grit hone to clean cylinder.
To prevent ring breakage, make sure all port edges are chamfered@ 30 deg angles
with a radius of .9 to 1.4mm

Installation
Check piston to cylinder clearance before assembly. Typical clearance range for snowmobiles as follows (Always refer to
manufactures specifications)
bore size Air cooled|||| Liquid Cooled
50-65mm .003"-.004"|| .004"-.005"
66 + up .0035"-.0045" ||.005"-.006"


Check ring end gap; single ring piston's range from .010" to .025"
two ring piston's range from .010" to .035"