1-5. Big Bore Piston Kit - TY250 Monoshock

Big Bore Piston Kit

 For all years & models of TY250 Monoshock

 TY250N TY250L TY250S TY250R Pinky Scottish

 Takes the capacity to about 263cc, 2mm over standard and offers a lot more bottom end grunt.

 Just requires a rebore to <70.00mm to fit

Pin to crown height is slightly less than the OEM piston but this keeps the power delivery nice and soft but with loads of torque.

Existing or new head gasket will need to be opened out to 70mm

Power can be increased by skimming the barrel & head but that obviously adds cost to he job. The only other mod we recommend with this conversion is to increase the squish on your cylinder head from 68 to 70mm. This is best done with a lathe or milling machine but you also get very good results with a Dremel multi-tool(please note other brands of multi-tool are available)

Wossner kit with forged piston

Kit consists of :-

Teflon Coated Piston ( Reduces Friction )

Rings

Pin

Circlip x 2

Small End Bearing

 Genuine Yamaha Pistons for this model are no longer available but we are working on something

This kit is available from stock in the following sizes

Std ( 69.94mm )

0.44mm o/s ( 70.44mm )

We don't recommend going any bigger than this as it leaves the liner a bit thin and it tends to go oval

We recommend a tight rebore of your barrel with a 1½ - 2 thou ( 0.0015 - 0.002" -  0.0381 - 0.0508mm) clearance, the tighter the better!

This kit is primarily for the early mode of YZ250 but we have tested it thoroughly on a TY250 Monoshock and it performs perfectly.

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