Tys125 Big Bore Kit.

[ausy300pro]

Yes but only just, the cylinder liner is pretty thin and will only go one rebore size, not really an issue though because second hand cylinders are easy enough to buy and a four stroke cylinder liner is easy and cheap to use, I did have to remove the balance shaft because the piston skirt will catch the balance weight due to the bigger diameter, I would probably try a slightly smaller bore size if I were to do it again, the problem is getting pistons, I am going to get a Honda atc200 piston to try for suitability as a spare.

[guido]

Yes but only just, the cylinder liner is pretty thin and will only go one rebore size, not really an issue though because second hand cylinders are easy enough to buy and a four stroke cylinder liner is easy and cheap to use, I did have to remove the balance shaft because the piston skirt will catch the balance weight due to the bigger diameter, I would probably try a slightly smaller bore size if I were to do it again, the problem is getting pistons, I am going to get a Honda atc200 piston to try for suitability as a spare.

So what bore size would you aim for in the future? I was under the impression that 163cc was the max, including the case bore, but it looks like you've discovered otherwise. I think a 163 kit is still available in the USA from B&J Racing. And I'm wondering if the smaller bore 143cc kit would be sufficient for a recreational duffer such as myself. Your thoughts?