138cc Big Bore Kit for Kawasaki Z125 Pro

138cc Big Bore Kit for Kawasaki Z125 Pro

SKU #: TPR-1008
Standard 138cc big bore kit! The 59mm bore will bolt onto the z125 Pro without machining your cases. Bolt on ready, no machine work needed. Just add Fuel controller.
$199.00 In stock


Availability: In stock

138cc big bore kit has all the important elements to achieve higher performance and more power! 

Kit specs and features:

  •  Bolt-in kit, no machined work needed
  • 59mm cylinder and piston.
  • Head gasket.
  • Cylinder Sleeve Outer Diameter: 61.8mm 
  • Wrist Pin Diameter: 13mm 
  • Total Piston Height: 38.4mm
  • Compression Height (from center of wrist pin hole to top edge of piston): 20.25mm


Steady Garage R&D:

Additional recommended operational parts:

  • Oil Cooler
  • Aftermarket Fuel Controller: Bazzaz Z-Fi or Dynojet Powercommander V w/Autotune (for those who don't have access to a dynameter)
  • Upgraded clutch parts: performance clutch springs and/or clutch disc

Optional parts for higher performance:

  • Large Bore or bore out throttle bodies
  • Aftermarket exhaust system
  • Chimera Short Ram Intake System

Professional installation is highly recommended!

Engine break-in, aftermarket fuel controller and special tune/autotune is required! Likewise with any major engine modification or bore up kits, it's now considered a high-performance race engine, extra attention and steps are needed to maintain a high-performance engine.



NO WARRANTY ON RACE ENGINE parts or engine bore up kits.  There is no warranty stated or implied due to the unusual stresses placed on these parts and because we have no control over how they are installed and used.  Steady Garage will not be held liable for any failure or damage caused directly or indirectly from use of these products or engine.  The installation and use of these products or engine shall be conclusive evidence that the user assumes full responsibility for any damage caused directly or indirectly by their use.


This product is legal for closed-course competition use only; for racing vehicles (a competition vehicle not used on public highways). Intended for off-road use or race purposes; may not meet regulations of pollution controlled roads or highways. Not legal for vehicles registered and use in California.