DHM Gen 2 High Compression Piston Kit for 2014-2020 Grom / 2019-2021 Monkey

DHM Gen 2 High Compression Stock Bore Piston Kit

The DH Motoring Gen 2 piston kit combines a 52.4mm stock bore with approximately 13.2:1 compression for a race-focused 125cc engine build. Its exclusive high-compression dome, enlarged oiling passages and 360-degree skirt are designed to support lubrication and strength during extended high-RPM use.

Race-developed design

Developed from six years of DH Motoring racetrack testing with more than a dozen stock bore piston designs, this kit targets increased lubrication while pushing compression for pump fuel. DH Motoring reports that its race-spec design has produced more horsepower than any other stock bore kit it tested and describes it as the highest-compression stock bore piston on the market. The dome is made exclusively for DH Motoring.

• Enlarged ring and skirt oiling holes feed the oil spring channel and skirt to support lubrication across the RPM range.
• A larger oil spring increases oil volume between the oiling rings.
• Oil ports beneath the pin holes help keep the wrist pin lubricated.
• A 360-degree skirt design increases overall strength.
• Valve reliefs accommodate cylinder head valves up to 27.5/23.5mm. DH Motoring states that the relief depth was designed for compatibility with high-lift cams.

Specifications and included parts

• Bore: 52.4mm, stock bore.
• Compression ratio: approximately 13.2:1.
• Generation: Gen 2.
• Includes racing piston ring kit, pins and circlips.
• Includes new base and head gaskets.
• Cylinder is not included; this listing is for the piston kit.

Application and spark plug options

Listed for 2014–2020 Honda Grom / Monkey applications. Confirm your specific model and engine configuration before installation.

Choose the piston kit without a spark plug or add an NGK CR9E spark plug using the existing option.

• Requires an NGK CR9E (6263) spark plug.
• Requires fuel rated at least 91 octane.

Installation and piston ring end gaps

Installing this piston requires setting the ring gaps. If you are not comfortable with this, have your local shop perform the installation. Failure to set the proper piston ring end gap can result in premature failure or engine seizure.

• Recommended top ring end gap: .007–.009 inches.
• Recommended bottom ring end gap: .009–.011 inches.
• The silver ring goes on top; the black ring goes below.

Unknown Overland explains the ring-gap procedure in the installation video below.