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DHM High Compression Stock Bore Piston for the 2022+ Honda Grom / Monkey (Gen 2)

$120.00
by DH Motoring
Include NGK CR9E Spark Plug

 

 **Professional install is highly recommended. Ring gaps must be set, and base gaskets must be installed properly. Setup sheet is included and can be viewed HERE.

DH Motoring Stock Bore Racing Piston (2022+ Grom / Monkey)

We've now produced the first high compression stock bore piston for the new 2022 Grom/Monkey. We took our development experience from the previous generation Grom and CRF110 and applied it to the all new Grom engine and have come up with a lightweight, high compression piston that still utilizes the OEM 12mm pin size. 

  • ~12.4:1 compression 50mm stock bore piston
  • 100% Forged construction
  • Larger ring and skirt oiling holes than other pistons on the market
  • Larger oil spring to increase oil volume between the oiling rings
  • OEM sized skirt area to maintain reliability
  • Racing piston ring kit with pins and circlips
  • Includes a new base and head gasket.
  • NGK CR9E spark plug required 
  • Requires at least 91 octane fuel
  • Requires ECU Flash or other Engine Management (aRacer, etc)


Increasing the compression ratio on the stock bore significantly increases the throttle response and overall power of the engine. In comparison to the stock piston, you can expect more low, mid and top end power while maintaining the use of your stock cylinder. We've designed this piston to be as close to the stock weight as possible without sacrificing any structural integrity. It can clear big valve head with 27/22 valve diameters and it will drop right in to your OEM cylinder. 

You will need either an ECU flash or some sort of fuel controller for this to run properly.

DHM ECU Flash

aRacer Standalone ECU


**Installing this piston requires setting the ring gaps. If you are not comfortable with this, please have your local shop perform the install. Failure to set the proper piston ring end gap can result in premature failure or seizure of the engine. We recommend an end gap of .007-.008" on the top ring and .009-010" on the bottom ring. The silver ring goes on top and the black ring below. 

Customer Reviews

Based on 21 reviews
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(18)
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S
Seth
Just looked at it haven’t installed yet

I’ve just looked at the piston and it seems fine but on online videos I’ve seen that it needs a spacer for the spark plug and I didn’t get one idk if the gen 2 is different but it isn’t confidence inspiring but other than that it seems perfectly good

M
Mochanic
Way overpriced for this quality!

I was a professional auto tech for 23yrs and 13 of those I owned my own shop building import race cars including more engines than I can count and NEVER even once did I have to deburr a brand new forged piston!
Virtually every corner on this piston was sharp and even had pieces clinging on the inside where the oil control holes were drilled and the sharp enough to cut you jagged flashing on the outer pin holes! For a piston this size and costing over a hundred dollars I was shocked especially coming from a company like DHM who so many people recommend! In very tiny print on the box it says made by OEM supplier, hmmm... Is this $15 piston really even forged?
We'll see how everything else goes, haven't really looked at the S1 cam yet.

T
Thomas Lindemann
DHM 2022 High Compression Stock Bore Piston

Excellent quality forging, excited to see how it runs combined with some other DHM products! Shipping was very quick, well packaged and included detailed instructions.

E
Eduardo

Waiting on the DHM S1 Camshaft for the 2022+ Honda Grom / Monkey (Generation 2) a d will install this and see what great upgrade it will be no doubt!

D
D.C.

I was wondering if I gap the oil rings to do all 4 rings need gaped

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