Chimera Engineering CBR Engine Swap Kit Honda Grom and Monkey

Chimera Engineering CBR Engine Swap Kit Honda Grom and Monkey


From: $345.00

To: $1,822.86

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Chimera Engineering CBR Engine swap kits would allow you to install a Honda NC51 (300cc) or Honda MC41(250cc) engine onto a 2014-2020 Honda Grom and 2019+ Honda Monkey! Enjoy the reliability of a water-cooled 250cc or 300cc Honda engine, with 6 speeds, and lots of power on your Honda Grom and Monkey!

  • GROM:

  • The engine mount kit includes everything needed to bolt-on a NC51 or MC41 engine onto a Grom chassis. This kit does NOT require any welding or major modifications to the chassis. It’s reversible! If you ever decide to put the original 125cc engine back on, you’re able to unbolt everything CBR related and reverse it!


  • Similar to the Grom, the engine mount kit includes everything you need to bolt-on an NC51 or MC41 engine onto a Monkey chassis. This kit does NOT require any welding, but some modification is needed on the very bottom portion of the Monkey frame. Slight cutting and grinding are required in order to clear the new engine.


Please see the additional information below for details! Price ranges from $345 - $1617.87 depending on options selected.

Chimera Engineering CBR Engine Swap Mounts Honda Grom   +$345.00

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Please review and read everything below carefully. There are many options listed in the drop-down menu so that you could customize the kit to work with your preference and set up.


Engine Mount Kit Content ($345.00):

  • 4x Chimera bolt-on engine mounting brackets NC51/MC41 engines
  • 9x Chimera Spacers
  • 5x Engine nuts and bolts
  • 2x Chain Guide Bearings
  • 1x Chimera Throttle Body Coupler
  • 2x Hose Clamps

Optional (See drop-down menus):

  • Chimera Front Mount Radiator for Honda Grom w/CBR engime swaps (+$149.99)
  • Chimera Radiator Hose Kit for Front Mount Radiator (+$55.00)
  • Chimera Race Header for Honda Grom w/Chimera CBR Engine Swap Mounts (+$225.00) 
  • Aftermarket ECU (+$249.95-$695)
  • Standard Length Chain (+$53.95-$100)
  • Front Sprocket (+$22.95)
  • Rear Sprocket (+24.99+$30.99)
  • EGR Block Off Plate ($39.99)
  • Coolant Over Flow Tank (TBA)
  • Breather Oil Catch Can (TBA)
  • H4 to SF Headlight adapter (55.00)

Donor parts that are needed (USER SOURCED, NOT INCLUDED WITH KIT):

  • -Honda NC51 or MC41 engines, commonly found on CBR250, CBR300, CB300, and Rebel 300.
    • NOTE: For all NC51 300cc engines before 2016, there is a CRANKSHAFT recall on them by Honda. If you’re purchasing a complete donor bike, you would want to take it to the dealer to perform the crankshaft recall before installing it onto the Grom. Aftermarket performance crankshaft is also available to stroke the engine (details would be provided in the near future). Special Thanks to Dominic in TN for pointing this out!
  • Honda CB300F OR CBR250/300 wire harness.
    • We recommend the CB300F harness because it requires the least amount of work to get it to function on the Grom chassis (due to the speedometer). Modification is required for the harness, so that it would cleaner and some wires will need to be extended/lengthen.
    • The CB300F harness allows you to reuse the original Grom speedometer OR a CB300F Speedometer. The CB300F speedometer is the same as the Grom unit, so it’s a direct-replacement, however it will display higher RPM reading (12k RPM) and it has a coolant temp light. If you decide to keep the Grom Speedometer, max RPM reading is 10k RPM and it doesn't have a coolant temp. light.
    • If you have the CBR250/CBR300 harness, then you're require to run a CBR250 or CBR300 speedometer, which would require a custom mounting bracket. Typical harness modification is needed as well.
    • Regardless of what harness you use, it would require all the supporting relays, sensors, and modification to the harness. 
  • Radiator and/or Radiator Fan:
    • If you go with Chimera Front Mount optional radiator, then you would need a radiator fan from one of these bikes: CBR250, CBR300, CB300, or Rebel 300.
    • If you decide to run your own radiator, then you would need to source something that could handle the cooling system of a 250cc or 300cc engine. If the radiator is too small, you will run the risk of overheating.
  • Throttle Body:
    • Any throttle body would work between the two models of engine.



1) The chain guide is made with bearings, therefore there’s direct bearing-to-chain contact. This would produce a chain whirling noise as the chain rolls over the bearings. Very little noise would occur during acceleration or cruising. However, during deceleration in gear (engine braking), the noise would be much louder. We thought of many ways to correct this, however all of the method would result in a wearable item, which we didn’t want.

2) If you decide to run the Chimera Front Mount Radiator, trimming to the inner plastic shrouds are required to clear the width of the radiator.

3) The OEM ECU from the NC51 or MC41 engines will not work alone. You would need to add a piggyback fuel controller OR run a full standalone such as ARacer. We highly recommend the following ECU

  • ARacer RC1 with AF1 option (RACE OPTION: Advance tuning features, full control of everything) 
  • ARacer RC Mini Plus 2 ECU with AF1 option (BEST OPTION: for price, tuning features, and user friendliness)
  • Aracer RC Mini 4C (BASIC OPTION: for price, something that would work, and simple tuning)

 4) 2017+ Model Grom owners who wish to retain the stock led headlight will require to purchase Tripage headlight conversion sku TRIP-1001.

WARNING: Due to the short standard wheelbase of the Grom, the new swap will have the tendency to wheelie during initial acceleration, rapid low speed accelerations, or while changing gears.


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