P51 Friction Clutch Pulley Upgrade Kit for OKMO Engine Models & Retrol HM-01

Perfect Compatibility Warning Why You Need This (User Benefits)

💡 Compatibility Note:

We do not recommend using this accessory on Lister D or B01 models. For important installation tips and compatibility details, please check out our Blog Notes before setting up your workbench! Subsequent batches of the Lister D will come equipped with welded gears, making them fully compatible.

💡 Version and Size Difference: OKMO vs. RETROL HM-01 Friction Clutch Pulley (P51)

Because the flywheel diameter of the RETROL HM-01 engine differs from standard OKMO series engines, this upgrade accessory is released in two distinct size versions. Please check your engine model before selecting:

• Standard OKMO Compatible Version: Designed for OKMO 1110, 1140, B01, B02, Z01, LD-A1, N01, and other compatible miniature engines.

  • Outer Diameter: 37 mm

  • Height: 46 mm (Unlocked) / 42 mm (Locked)

• RETROL HM-01 Dedicated Version: Because the HM-01 features a larger flywheel diameter, this dedicated version is sized up accordingly to ensure a precise, seamless fit.

  • Outer Diameter: 40 mm

  • Height: 50 mm (Unlocked) / 46 mm (Locked)

Both versions share the same precision-machined all-metal P51 construction and power-engagement features, but they are not interchangeable due to the engine flywheel differences. Please select the correct version that matches your specific engine model.

Why Upgrade Your Stock Pulley?

• Effortless, Strain-Free Engine Starts: Disengage the clutch before starting to remove all load resistance from generators, pumps, or gearboxes. Enjoy smoother, easier pull-starts without stalling your engine.
• Authentic "Neutral to Drive" Realism: Experience realistic mechanical operation. Switch effortlessly between Disengaged (Neutral) and Engaged (Drive) modes to simulate real-world automotive clutch engagement during engine demonstrations.
• Hassle-Free Engine Tuning & Idle Control: Need to adjust your carburetor or test idle stability? Disengage the drive system so you can safely tune your engine without spinning belts or attached driven components.
• Direct Bolt-On / Quick Installation: No drilling or custom machining required. Simply swap out your stock fixed pulley, align with the factory mounting holes, adjust belt tension while disengaged, and lock it down.
• Durable All-Metal Precision Machining: Built from high-grade alloy metal using original factory tolerances for reliable power transfer, thermal endurance, and zero belt slippage under heavy operation.

Technical Specs Table

Specifications

Model Code	OKMO-P51
Type	Manual Friction Clutch Belt Pulley Assembly
Material	Machined Alloy Metal
Outer Diameter	37 mm
Adjustable Height	46 mm (Disengaged) / 42 mm (Engaged)
Weight	280g (Net) / 350g (Package)
Recommended Age	16+

What's in the Box

What's Included

• 1 × OKMO P51 Manual Friction Clutch Pulley Assembly
• 1 × Mounting Screw & Hardware Pack