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Product Description
Bore: Yes
Stroke: No
Actual Displacement = 139.07cc
Engine Modifications Required:
Cylinder: Bore, Port and Replate with Apticote 2000 ceramic bore coating.
Power Valves: Machined to match big bore ports.
Head: Rechamber to work with the Big Bore piston. 100 octane suggested for most conditions.
Crankshaft: No crank mods required.
Crankcase: No crankcase mods required.
Blueprint: Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. (Some operations with install only)
Notes: This kit requires you to send us your cylinder, head, and powervalves for modification.
Notes: Core parts subject to inspection before credits will be issued.
Notes: This is as large as we go with the bore on a stock stroke YZ125. By stopping at 57mm we keep all the fun parts of the YZ125 and just add a bunch of power everywhere. Line the YZ139 up against any big boreYZ144 and the difference will become clear quite quickly, the 139 revs way farther and pulls longer with little to no vibration.
Stroke: No
Actual Displacement = 139.07cc
Engine Modifications Required:
Cylinder: Bore, Port and Replate with Apticote 2000 ceramic bore coating.
Power Valves: Machined to match big bore ports.
Head: Rechamber to work with the Big Bore piston. 100 octane suggested for most conditions.
Crankshaft: No crank mods required.
Crankcase: No crankcase mods required.
Blueprint: Calculate deck height, squish clearance, trapped volume, port timing and compression ratio and list on your perminant Spec-Sheet. (Some operations with install only)
Notes: This kit requires you to send us your cylinder, head, and powervalves for modification.
Notes: Core parts subject to inspection before credits will be issued.
Notes: This is as large as we go with the bore on a stock stroke YZ125. By stopping at 57mm we keep all the fun parts of the YZ125 and just add a bunch of power everywhere. Line the YZ139 up against any big boreYZ144 and the difference will become clear quite quickly, the 139 revs way farther and pulls longer with little to no vibration.