Cylinder reboring

Just grand...The new piston from Wössner. I had been puzzling over this issue for quite a long time: for srx 600 model, there is no problem to get a new piston for reboring - besides the larger OEM size, there is also a Wiseco option. Well, for japanese 400cc, you may get the OEM piston (5Y6-11631-01-A0), on the other hand, that is the standard piston size which is no use - in this case, the whole new cylinder barrel with a smaller boring would be required to get it working. So, here is the deal: since there is no aftermarket variant for srx/xt 400 available, we laid up heads together with Oulehla Motor Parts, the well known machining specialist in Sternberk, Czechia. It turned that the Honda xr 400 dirt bike has the same boring, though a small adjustation of the piston top showed as necessary. It was needed to cut a new spaces for valves identical to OEM part on a milling machine. The new piston comes with the piston pin, ring set and circlips.

A genuine srx piston compared to the lower Wössner

The milled valve spaces in a front-rear direction (srx) as oppose to the diagonally oriented, bigger genuine spaces (xr)