Alternator V-belt Yanmar 2YM15 | 3YM20 | 3YM30 – A37.5

Description

Replacement alternator belt for the Yanmar YM series sailboat engines. On the 2YM15, 3YM20, and 3YM30, this belt drives the alternator and runs over the crankshaft pulley. The raw water pump on these engines is not driven by this belt — it has its own, much shorter belt on the other side of the block.

Classic A-profile of 13 x 8 mm in Yanmar size A37.5. Yanmar indicates belts as a profile letter plus the nominal length in inches, so A37.5 stands for 37.5 inches (approx. 952 mm).

✔️ Correct size for the marine version — the industrial version of the same engine block uses a shorter belt
✔️ Covers the complete YM sailboat series: 2YM15, 3YM20, and 3YM30 with both the 60A and 80A alternators
✔️ Standard A-profile, easy to tension correctly with the original adjustment bracket

Dimensions

• Designation: A37.5
• Profile: classic A, 13 x 8 mm
• Nominal length: 37.5 inch (approx. 952 mm)

Belt lengths are specified in different ways: Li is the inner circumference, Lw/Ld is the pitch length, and La is the outer circumference. When in doubt, measure the old belt.

Suitable for

• Yanmar: 2YM15, 3YM20, 3YM30

Please note

• Late 3YM30 and all 3YM30AE models do not use a V-belt. From serial number E20848, Yanmar fitted a Valeo alternator with a flat pulley, which requires a 6-rib multi-rib belt (128990-77580). Check your engine number before ordering.
• These engines have two belts. In addition to this alternator belt, there is a short belt on the raw water pump. It is recommended to replace them together — if the raw water pump belt fails, it is the more expensive of the two because you will lose engine cooling.
• Yanmar uses a different part number for each model for the same size: the 2YM15 uses 129612-42290, the 3YM20 and 3YM30 use 119831-42290. They are not interchangeable part numbers, but they are the exact same belt size.

Maintenance

Yanmar specifies for the YM series: check tension every 250 operating hours or annually, and replace the alternator belt every 1,000 operating hours or every four years. The correct tension provides 8 to 10 mm of deflection.

OEM for reference

• 129612-42290 (2YM15)
• 12961242290
• 119831-42290 (3YM20, 3YM30)
• 11983142290