Alternator V-Belt – Fits Yanmar 3JH2, 3JH3, 3JH4E Marine Diesel Series (Replaces 129940-42310, 129940-42310E)
Alternator V-Belt – Fits Yanmar 3JH2, 3JH3, 3JH4E Marine Diesel Series (Replaces 129940-42310, 129940-42310E) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Alternator V-Belt – Fits Yanmar 3JH2, 3JH3, 3JH4E Marine Diesel Ser...
Product Details
This is a genuine replacement Alternator V-Belt designed for a range of Yanmar marine diesel engines, specifically the 3JH series models including 3JH2-E, 3JH2-TE, 3JH3E, and 3JH4E (1999–present). It ensures reliable power transmission from the crankshaft to the alternator, maintaining your engine's electrical system performance.
This part is a direct interchange for Yanmar part numbers 129940-42310, 129940-42310E, 171087-42280, and 25152-004400.
- Installs as a direct OEM-equivalent replacement.
- Constructed as a durable, toothed V-belt for secure grip.
- Approved for OEM quality by third-party evaluators (SVB).
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Yanmar | 129940-42310 |
| Yanmar | 129940-42310E |
| Yanmar | 171087-42280 |
| Yanmar | 25152-004400 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
| Brand | Model | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Yanmar | 3JH2-E | 4-Stroke | 129940-42310 | ||
| Yanmar | 3JH2-TE | 4-Stroke | 129940-42310 | ||
| Yanmar | 3JH3E-YEU-E | 4-Stroke | 1999–2003 | 129940-42310 | |
| Yanmar | 3JH3 | 4-Stroke | 129940-42310 | ||
| Yanmar | 3JH25A | 4-Stroke | 129940-42310 | ||
| Yanmar | 3JH4E | 4-Stroke | 2004–present | 129940-42310 | |
| Yanmar | 4TNV98-VTBZ | 4-Stroke | 129940-42310 | Per Diesel Parts Direct | |
| Yanmar | 4JH3 | 4-Stroke | 129940-42310 | Per JLM Marine |
Technical Specs
- Product Type
- Alternator V-Belt
- Installation
- Direct OEM replacement
- Belt Type
- V-Belt
- Belt Width
- 13 mm
- Length
- 1.14 m
- Tooth System
- Yes
- Fitting Type
- Standard V-belt installation
- Warranty
- 6-month warranty (Diesel Parts Direct)
- Other Technical Attributes
- "OEM quality" approved (SVB)
What’s in the Box
- 1 x Alternator V-Belt (Replaces 129940-42310 / 129940-42310E)
Installation Notes
- Ensure the engine is off and fully cooled. Disconnect the battery.
- Slightly loosen the alternator pivot bolt and any tensioner bolts.
- Note the existing belt's path around the pulleys.
- Relieve tension by moving the alternator and slip the old belt off.
- Inspect and clean all pulley grooves, removing any rust or debris.
- Route the new belt along the same path, ensuring it seats correctly in the V-grooves.
- Tension the new belt by swiveling the alternator. Proper tension allows for about 1 cm (½″) of deflection under moderate thumb pressure at the longest span.
- Tighten the adjuster-plate bolt first, then the main pivot bolt to spec.
- Reconnect the battery.
- Start the engine and check that the belt is tracking smoothly and centered.
- Shut the engine down and re-check tension, as new belts may stretch slightly after their first run.
Troubleshooting & FAQ
How can I confirm this belt fits my Yanmar engine?
This belt fits the engines listed in the 'Engine & Model Compatibility' table, including various 3JH, 4JH, and 4TNV models. The most reliable method is to match your existing part number to one of the cross-references: 129940-42310, 129940-42310E, 171087-42280, or 25152-004400.
What are the signs of a worn-out alternator belt?
Common signs include a loud squealing noise from the engine bay (especially on startup), visible cracks or fraying along the belt's edges, a glazed or shiny appearance on the belt's surface, or a noticeable loss of battery charging performance.
What is the correct tension for this V-belt?
A correctly tensioned V-belt should have approximately 1 cm (½ inch) of deflection when you press firmly with your thumb on the longest span between pulleys. Over-tightening can damage the alternator and water pump bearings, while a loose belt will slip and fail to power the alternator effectively.
How often should I replace my alternator belt?
There is no fixed interval; replacement should be based on condition. Inspect the belt during every routine engine service. Replace it immediately if you see signs of cracking, glazing, or wear. Proactive replacement every few hundred hours or every few years can prevent unexpected failure at sea.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). It's built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 facility, with batch inspections for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
This product is 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 for unused items 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.
Payment & Security
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