CBR 250/300 Engine Swap Mount For Honda Grom 2014-2020 and Honda Monkey 2018-2021

 

CBR Engine Swap Kit for Honda Grom (2014–2020) & Monkey (2019–2021)

Transform your Honda Grom or Monkey with the ultimate engine swap kit. Our Chimera CBR Engine Swap Kit allows you to install a Honda NC51 (CBR300/CB300) or Honda MC41 (CBR250) engine into your Grom (2014–2020) or Monkey (2019–2021), unlocking the power and reliability of a water-cooled, 6-speed Honda engine!

Key Features:

• Compatible with Honda NC51 (300cc) and MC41 (250cc) engines
• 6-speed transmission for improved top speed and acceleration
• Water-cooled performance and reliability
• No welding required (Grom); minor frame mod needed (Monkey)
• Fully reversible install on Grom models

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Fitment & Installation Notes

GROM (2014–2020):

• Direct bolt-on install — no welding or major chassis mods required
• 100% reversible — reinstall your 125cc engine anytime

MONKEY (2019–2021):

• Direct bolt-on with minor modifications to the underside of the frame (cutting/grinding needed for clearance)

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What’s New in the design:

• 25% lighter design
• Improved clearance between frame and engine
• Dual stacked plate system reduces vibration and prevents frame stress cracks — a major issue with single-piece thick plate designs used by others
• Weight: Just 1.8 lbs
• Can be Painted to your color.

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Engine Mount Kit Contents — $199.99:

• 4x CBR Bolt-On Engine Mounting Brackets (NC51 / MC41)
• 9x  Spacers
• 5x Engine Mounting Nuts and Bolts
• 2x Chain Guide Bearings

Note: This listing is for the engine mount kit only. Additional components must be sourced separately.

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Required Donor Parts And Aftermarket Parts (User-Sourced):

 

• Honda NC51 (CBR300/CB300/Rebel 300) or MC41 (CBR250/CRF250L) engine

⚠️ NC51 engines (2013–2015) may have a crankshaft recall — verify with a Honda dealer before use.

• Honda CB300F or CBR250/300 Wiring Harness
  • CB300F harness is recommended for easier speedometer integration
  • Grom and CB300F speedometers are interchangeable
  • CBR250/300 harness requires additional wiring and mounting modifications
• Radiator & Radiator Fan
  • If using Chimera Front Mount Radiator, get a fan from: CBR250, CBR300, CB300, or Rebel 300
  • If using another radiator, ensure it can handle 250cc–300cc engine cooling
• Throttle Body
• Compatible across both NC51 and MC41 engine types
  

  Aftermart Parts Needed:

• CNC Billet Aluminum Intake Manifold or Silicone Elbow Coupler
• Modified Front Mount Radiator
• Radiator Hose Kit
• CBR Swap Header for Grom
• Aftermarket ECU (Recommended: ARacer)
• Standard Length Chain
• Front & Rear Sprockets
• EGR Valve Block Off Plate
• Coolant Overflow Tank
• Breather Oil Catch Can
• H4 to SF Headlight Adapter

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Important Notes:

• Chain Guide Noise: Bearings in the guide make a noticeable sound under engine braking. This is normal and part of the design.
• Radiator Fitment: Inner plastic trim must be modified for Front Mount Radiator clearance
• ECU Compatibility:
  • OEM ECUs from NC51/MC41 will not run standalone
  • Recommended ECUs:
    • ARacer RC Super 2 with AF2 (full race-tuning)
    • ARacer Mini 5 or Mini-X with AF2 (best value + easy tuning)
• 2017+ Grom LED Headlight Compatibility: Requires Tripage TRIP-1001 headlight adapter
• NOT Compatible with 2022+ Grom or Monkey models

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⚠️ WARNING:

The added power from the engine swap significantly increases torque and acceleration. Expect wheelies during launch or gear shifts on short wheelbase setups.
For off-road use only.