Balmar AltMount Serpentine Pulley Conversion Kit for Yanmar 3JH5, 3JH4-E, 4JH4-E, 4JH5, 4JH5-E

AltMount® Serpentine Pulley Conversion Kit for High-Output Marine Alternators

Reliable Power Transmission for Yanmar 3JH and 4JH Series Diesel Engines

Upgrading your marine electrical system with a high-output alternator requires a drive system capable of handling the increased mechanical load. Standard V-belts are prone to slipping, stretching, and shedding destructive black belt dust when subjected to the heavy torque demands of modern lithium (LiFePO4) or large AGM battery banks. The AltMount® Serpentine Pulley Conversion Kit provides a robust engineering solution designed specifically for select Yanmar marine diesel engines, including the 3JH5, 3JH4-E, 4JH4-E, 4JH5, and 4JH5-E models.

By converting your factory V-belt setup to a modern ten-groove (J10) serpentine belt system, this kit significantly increases the surface contact area between the belt and the pulleys. This enhanced grip maximises power transmission efficiency, eliminates belt slippage, and reduces the radial load on both your engine's water pump bearings and your alternator's internal components.

Engineered for Harsh Marine Environments

Marine engine bays present unique challenges, from constant vibration to corrosive salt air. Unlike standard automotive components that quickly degrade at sea, the AltMount® system is purpose-built for longevity in demanding off-grid and marine applications. Each kit features three precision-machined, blue anodised aluminium pulleys that resist corrosion while maintaining strict tolerances for smooth, balanced operation.

• Ten-Groove (J10) Serpentine Design: Delivers superior grip and torque transfer to support high-amperage alternators without slipping.
• Precision-Machined Anodised Pulleys: Includes three custom-engineered pulleys (crankshaft, water pump, and a 17 mm alternator rotor shaft pulley) built to resist wear and marine corrosion.
• Complete Redundancy Included: Supplied with two heavy-duty 44.5" (approx. 1.13 m) circumference J10 serpentine belts, giving you an immediate onboard spare for peace of mind during remote cruising.
• Comprehensive Installation Hardware: Comes complete with high-tensile mounting bolts, Loctite 242 threadlocker for vibration resistance, and Tef-Gel anti-corrosion lubricant to prevent galvanic seizure between dissimilar metals.
• Direct Supersession: Directly replaces previous kit versions 48-YSP-3JH-B, 48-YSP-4JH-C, and 48-YSP-4JH-A.

Why Upgrade to a Serpentine System?

When a standard 12V or 24V alternator is working at full capacity, it places immense physical drag on the engine belt. Standard belts often require frequent re-tensioning and premature replacement under these conditions. Switching to an AltMount® J10 serpentine conversion kit solves these common failure points:

• Eliminates Belt Dust and Squeal: Proper engagement prevents the friction that causes annoying belt squeal and coats your engine room in fine rubber dust.
• Protects Engine Bearings: Serpentine belts transfer power efficiently with less tension than V-belts, reducing side-load stress on expensive water pump and alternator bearings.
• Improves Charging Consistency: By preventing slippage, your alternator spins at the optimal RPM, ensuring your batteries receive their full rated charge current faster and reducing overall engine run time.

Complete Your Marine Charging Upgrade

Whether you are fitting a high-output Balmar alternator or upgrading your vessel's off-grid energy capacity for extended passages, a reliable mechanical drive is essential. Upgrade your Yanmar engine with the AltMount® Serpentine Pulley Conversion Kit today to ensure efficient, trouble-free power generation on the water.