172cc Forged Piston Cylinder - ProBld

Want real power gains from your GY6 without risking reliability? 💪 This 172cc ProBld drop-in kit is the strongest and most heat-stable upgrade for the QMJ157 engine — no case boring, no machining. The 4032 forged piston delivers long-life strength under hard riding, smoother torque, quicker acceleration, and cooler running than any cast-piston setup.

The Details

This isn’t just another big-bore kit — it’s purpose-built for riders who want real performance without sacrificing longevity. The ProBld 61mm (172cc) cylinder is the largest true drop-in option for QMJ157 GY6 engines, meaning you won’t need to split cases or machine anything to make it fit.

Standard kits use soft cast pistons and low-quality cylinders that wear fast and run hot. This setup uses a premium 4032 forged piston — the same alloy used in high-end automotive builds — giving it superior strength, heat stability, and smooth operation for long-mile daily riding or full performance builds.

The piston rings come pre-measured and installed to ensure correct end-gap. No filing, no guesswork — just bolt it in and ride. You’ll feel stronger mid-range pull, quicker acceleration from a stop, and noticeably more torque everywhere in the RPM range.

• 4032 forged piston for high-strength reliability
• Pre-installed rings eliminate installation mistakes
• Improved heat dissipation + harder cylinder wall
• Compatible with stock or performance cams/heads
• Designed to handle extended wide-open-throttle riding

Important Things to Note

• Must be a QMJ157 engine — this will not fit other GY6 variants.
• If you have a buggy/go-kart: stud spacing varies between manufacturers.
• We recommend testing with a 61mm gasket test kit before purchase.

Need help confirming? Click here to decode your engine.

What's Included

• ProBld 61mm Cylinder
• 4032 Forged Piston
• Pre-Installed & Pre-Gapped Piston Rings
• Wrist Pin & Circlips
• Base Gasket & Head Gasket

Everything required for installation — no additional machine work needed.