Yanmar V-belt A39.5 for 3HMF – 128695-44780

Description

Yanmar V-belt A39.5 for 3HMF

The genuine Yanmar V-belt 128695-44780 is a drive belt with size designation A39.5 for the Yanmar 3HMF marine diesel engine. This version is specifically intended for the indirectly cooled 3HMF and is used to mechanically drive the alternator.

A properly functioning V-belt ensures that the engine’s rotational movement is reliably transferred to the alternator. This allows the alternator to generate electrical energy to charge the batteries and supply power to electrical equipment on board.

Technical specifications

Brand: Yanmar
Product type: V-belt / alternator belt
Size designation: A39.5
Cooling system type: Indirectly cooled
Function: Mechanical drive of the alternator
Application: Charging system of marine diesel engines
Maintenance: Periodic inspection and replacement according to the maintenance schedule

Suitable for Yanmar marine engines

This V-belt is suitable for the following Yanmar marine diesel engine:

Suitable for:
Yanmar 3HMF

The Yanmar 3HMF is an indirectly cooled three-cylinder marine diesel engine. The V-belt with size designation A39.5 is specifically intended for the alternator drive of this engine version.

Please note: This V-belt is not suitable for the Yanmar 3HM or 3HM35F. These engine versions use a different V-belt. Always check the exact engine type before ordering the part.

Function of the V-belt

The V-belt transfers rotational movement from the crankshaft pulley to the alternator. While the engine is running, this allows the alternator to generate electrical energy to charge the batteries and supply power to the electrical system on board.

For reliable power transmission, the V-belt must have sufficient grip on the pulleys. Correct belt tension is therefore important.

If the V-belt is insufficiently tensioned, it may slip. This reduces the efficiency of the alternator drive and may decrease the charging current. If the V-belt breaks, the affected alternator drive stops functioning completely.

When should the V-belt be replaced?

A V-belt is continuously subjected to mechanical stress while the engine is running. Friction, heat, ageing and prolonged use can cause the material to wear or become damaged.

Regularly inspect the V-belt for the following signs:

Cracking: Cracks or damage in the rubber.
Wear: Worn drive surfaces or damaged edges.
Slipping: A squealing noise when starting or running the engine.
Incorrect tension: A V-belt that is too loose or too tight.
Damage: Visible deformation, fraying or separating material.

If the V-belt is only insufficiently tensioned and is otherwise in good condition, the belt tension can be adjusted according to the maintenance instructions. If cracks, damage or excessive wear are present, the belt must be replaced.

Installation and maintenance

Before installation, check that the new V-belt matches the specified version for the Yanmar 3HMF. Pay attention to the A39.5 size designation, belt profile and installed pulleys.

Inspect the pulleys for damage, contamination and unusual wear. Damaged or misaligned pulleys can shorten the service life of the V-belt.

Install the V-belt according to Yanmar’s maintenance instructions and adjust the belt tension correctly. A V-belt that is too loose may slip, while excessive tension can place additional stress on the alternator bearings.

After installation, check that the V-belt runs correctly in the pulleys and that the alternator provides sufficient charging current. Recheck the belt tension according to the specified maintenance procedure.

Spare V-belt on board

It is advisable to keep a suitable spare V-belt on board, especially during longer voyages. If a V-belt unexpectedly breaks or becomes damaged, a spare belt can help restore the alternator drive.

Store the spare V-belt in a dry place, protected from direct sunlight, oil and excessive heat. Avoid sharply bending or deforming the belt during storage.

Important considerations

The A39.5 size designation is an important reference when replacing the belt. Only use this V-belt if it matches the specified version for the installed engine and alternator configuration.

The Yanmar 3HM and 3HM35F use different V-belts and are not compatible with this version. A V-belt with a similar shape or length is not automatically interchangeable. The belt profile and fit on the pulleys must also match.