Quote:
Originally Posted by Dave Wolfe
So I was stuck on my sofa over the weekend and did a little digging:
1) It seems Bruce has purchased all the 300 cranks on Ebay 
2) the stock 300 pistons are nom. ~.001" larger in diameter than the newgen 250 stock pistons. Specs in the manual for ring groove width are equivalent for the 300 and newgen 250.
3) the cylinder dia spec is slightly smaller for the 300
4) the ring thickness specs are pretty equivalent. I think the 300 had a slightly higher ring endgap spec for one of the rings. The 250 and 300 stock ring sets have different part numbers and i have no idea if anything is really different between the two.
So if I were to do a cheap 300 crank swap, id try to use the stock 300 pistons and rods, have the 250 cylindrrs honed a touch if needed for piston to cyl clearance. Im not sure if the valves would clear or what kind of CR would result. |
No.This will not work as stated above.
There are plenty of cranks on ebay, they just happen to be in complete engines. You can put one in you 250 frame easily and this would probably be the easiest on your budget. The 300 has nikasil cylinder wall requiring special low tension rings. also your pistons will end up sticking out the top of the cylinders, you will need to adjust for that. Search the forum for my 335cc build, you can do the same thing with stock bore=300cc, 2mm over=315cc (good choice, have built a few of these), or 4mm over=335cc ( a little finicky) or 5mm over=345cc this is kind of special and i'm not sure if the cylinder block is obtainable easily.