Alternator Belt – Fits Yanmar 2GM20F, 3GM30F (Replaces Yanmar 25132-003700)
Alternator Belt – Fits Yanmar 2GM20F, 3GM30F (Replaces Yanmar 25132-003700) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Alternator Belt – Fits Yanmar 2GM20F, 3GM30F (Replaces Yanmar 25132...
Product Details
This Alternator Belt – Fits Yanmar 2GM20F, 3GM30F Marine Engines (Replaces 25132-003700) is a V-belt designed for Yanmar 2GM20F and 3GM30F series marine diesel engines from the 1980s to 2005. It is compatible with both fresh water cooled and heat exchanger cooled models, including standard and European-manufactured (YEU) variants.
This part is a direct replacement for Yanmar part numbers 25132-003700, 25132-003700E, and 124732-42290.
- Durable Material: Constructed from high-strength Neoprene with Polyester Cord for longevity.
- Precise Tensioning: Installs with moderate tension, deflecting approximately 1 cm (1/2 inch) under thumb pressure.
- Wide Temperature Range: Rated for reliable operation in temperatures from -40°C to 60°C (-40°F to 140°F).
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yanmar | 25132-003700 / 25132-003700E | OEM Reference |
| Yanmar | 124732-42290 | OEM Reference |
| Gates | 6463MC | Aftermarket alternative noted for reduced dust and long wear. |
| Mitsubishi | REMF6370 | Aftermarket alternative. |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This V-belt is specifically designed for Yanmar 2GM20F and 3GM30F series engines, ensuring proper fit and function.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yanmar | 2GM20F | 20 | 4-Stroke | 1980s–2005 | 25132-003700 | Fresh Water Cooled |
| Yanmar | 3GM30F | 27 | 4-Stroke | 1980s–2005 | 25132-003700 | Fresh Water Cooled |
| Yanmar | 2GM20F-YEU | 20 | 4-Stroke | 1980s–2005 | 25132-003700 | Heat Exchanger Cooled |
| Yanmar | 3GM30F-YEU | 27 | 4-Stroke | 1980s–2005 | 25132-003700 | Heat Exchanger Cooled |
Technical Specs
- Product Type
- V-Belt
- Belt Type
- A-Series (Standard V-Belt)
- Belt Profile
- A37
- Belt Length
- 37 inches (940 mm)
- Material
- Neoprene with Polyester Cord
- Top Width
- 12.5 mm (1/2 inch)
- Depth
- 9.5 mm (3/8 inch)
- Angle
- 40°
- Color
- Black
- Warranty
- 12 months against manufacturing defects (aftermarket)
What’s in the Box
- 1 x Alternator Belt (25132-003700)
Installation Notes
- Ensure the engine is off and completely cooled. Disconnect the battery.
- Slightly loosen the alternator pivot bolt and any tensioner bolts.
- Note the belt's path around the crankshaft, water pump, and alternator pulleys.
- Relieve tension by swiveling the alternator and slip the old belt off the pulleys.
- Inspect pulley grooves for wear or corrosion. Clean them as needed.
- Route the new belt along the same path, ensuring it seats correctly in the V-grooves.
- Tension the new belt by swiveling the alternator away from the engine.
- A correctly tensioned belt should deflect about 1 cm (½″) with moderate thumb pressure on the longest span.
- Tighten the adjuster-plate bolt first, followed by the main pivot bolt to factory torque specs.
- Reconnect the battery.
- Start the engine and observe the belt to ensure it tracks smoothly in the pulley grooves.
- Shut down the engine and re-check tension after a short run-in period. Adjust if necessary.
Troubleshooting & FAQ
What are the signs of a worn or failing alternator belt?
Common signs include high-pitched squealing noises (especially on startup), visible cracks or fraying on the belt surface, a glazed or shiny appearance in the V-groove, or loss of alternator charging performance.
How do I properly tension this V-belt?
As a general rule, press firmly on the longest span of the belt between pulleys. A correctly tensioned belt should deflect approximately 1 cm (½ inch). Over-tensioning can cause premature wear on bearings, while under-tensioning can lead to slippage and poor performance.
Will this belt fit my specific Yanmar engine?
This belt is designed for Yanmar 2GM20F and 3GM30F series engines, including the -YEU variants. Always confirm your engine model and reference the OEM part number (25132-003700) to ensure compatibility.
Are there any recommended aftermarket alternatives for this belt?
Yes, some boaters have reported positive experiences with alternatives like the Gates 6463MC (often cited for reduced dust) and the Mitsubishi REMF6370. This listing provides an equivalent A37 profile belt.
What is the recommended replacement interval?
There is no fixed interval, but it is best practice to inspect your alternator belt during every routine engine check. Replace it at the first sign of cracking, glazing, or significant wear to prevent unexpected failure.
Why do aftermarket belts sometimes have serrations (cogs) when the OEM doesn't?
Serrations or cogs on a V-belt can increase flexibility and help dissipate heat, potentially leading to a longer service life. Both smooth and cogged designs that meet the A37 profile specification will function correctly on your engine.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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