4 stroke cylinder wear - opinions needed

Bristol GB
10/2/2017 3:54pm
A friend of mine wanted more power out of his 2015 FC250 Husqvarna, and a Cylinder Works 270cc kit came up on eBay from a KTM (same cylinder). Clearly the piston is toast and will need replacing in any case, but my concern is that the seller has run this thing miles past the piston service life and damaged the bore. The piston skirts have been polished smooth by rocking, and when the piston sits in the cylinder, the gap from the edge of the piston to the cylinder seems excessive - easily 1mm by eyeball. Admittedly, there are no rings fitted to the piston, but it still seems too big. This is a B Size Vertex piston - 80.97mm piston for an 81mm bore.

I don't have any tools to hand to measure the cylinder, and I don't want to order a new ring set just to measure the end gap. Just after some opinions and the knowledge of more experienced engine builders. Would you buy a C or D size piston kit and run this thing or should I send it back and ask for a refund?


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