This service is for 1997 - 2018 YZ 125 MOTORCYCLE CYLINDER Big bore .

Cylinder sleeve is installed then Overbored +2mm to 56 mm. Bore NOW 134cc. 

Use a 56 mm Wiseco Piston on this 134cc Cylinder

Send your 56mm piston, remove power valve & studs

Power Valves Must Be Modified/ Recessed 1 mm to prevent Piston Damage!

Head must be  Re-chamfer to work with the Big Bore piston set up to your octane requirements.

Crankshaft -No crank modification required.

Crankcase - No crankcase modification required.


We can Precision machined your powervalve to match big bore ports ( @ extra cost) 

This kit requires you to send us your cylinder, head.



YZ-134 Big Bore Jug ( 1997 - 2018)

  • Note: Product images only reflect class of products. If in doubt ask before purchasing. Our cylinder sleeves are made from chrome-moly alloy. Our Ports are machined with close tolerance and shapes allowing easy of installation and greatly reduce the need for additional porting after installation.