Alternator V-Belt – Fits Yanmar 2YM15, 3YM20, 3YM30 (Replaces Yanmar 129612-42290E)
Alternator V-Belt – Fits Yanmar 2YM15, 3YM20, 3YM30 (Replaces Yanmar 129612-42290E) 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 2YM15, 3YM20, 3YM30 (Replaces Yanma...
Product Details
This aftermarket Alternator V-Belt is a direct-fit replacement for Yanmar 2YM15, 3YM20, and 3YM30 marine diesel engines produced after June 2004 with serial numbers before E20848. For engines with serial numbers E20848 and later, a different flat serpentine belt (128790-77580) is required instead.
It directly replaces OEM part number Yanmar 129612-42290E, which supersedes the earlier part 119831-42290 used on pre-June 2004 engines.
- Installation Method: Direct replacement
- Material: Durable rubber with internal fiber reinforcement
- Application: Primary alternator drive belt for marine diesel engines
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By | Notes |
|---|---|---|---|
| Yanmar | 119831-42290 | 129612-42290E | For engines before June 2004 |
| Yanmar | 129612-42290E | For engines after June 2004 (before serial #E20848) |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This belt is designed for specific Yanmar YM series marine diesel engines. Please note the serial number and production date cutoffs to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yanmar | 2YM15 | 14 | 4-Stroke | After June 2004 (before serial #E20848) | 129612-42290E | Primary alternator drive belt |
| Yanmar | 3YM20 | 21 | 4-Stroke | After June 2004 (before serial #E20848) | 129612-42290E | Primary alternator drive belt |
| Yanmar | 3YM30 | 29 | 4-Stroke | After June 2004 (before serial #E20848) | 129612-42290E | Primary alternator drive belt |
| Yanmar | 2YM15 | 14 | 4-Stroke | Before June 2004 | 119831-42290 | Earlier version for pre-June 2004 engines |
| Yanmar | 3YM20 | 21 | 4-Stroke | Before June 2004 | 119831-42290 | Earlier version for pre-June 2004 engines |
| Yanmar | 3YM30 | 29 | 4-Stroke | Before June 2004 | 119831-42290 | Earlier version for pre-June 2004 engines |
Technical Specs
- Product Type
- Alternator V-Belt
- Installation
- Direct replacement
- Fuel Type
- Diesel
- Housing Material
- Rubber with internal fiber reinforcement
- Dimensions
- Standard V-type profile
- Warranty
- Varies by retailer (6 months to 1 year typical)
- Other Technical Attributes
- Marked as "BANDO RPF 3375 13X925Li" on some OEM belts
What’s in the Box
- 1 x Alternator V-Belt (129612-42290E)
Installation Notes
- Disconnect the boat's battery or turn off the main power switch for safety.
- Locate the alternator and identify the pivot and tensioning bolts.
- Slightly loosen the tensioner pulley bolt and the main alternator pivot bolt.
- Push the alternator towards the engine block to release tension on the old belt.
- Carefully slip the old, worn belt off the pulleys.
- Install the new belt, ensuring it is properly seated in the grooves of the crankshaft and alternator pulleys.
- Apply leverage to the alternator to set the correct tension on the new belt (a common rule of thumb is ~1/2 inch or 1.3 cm of deflection at the longest point).
- While maintaining tension, securely tighten the tensioner and pivot bolts.
- Reconnect the battery power, start the engine, and visually verify the belt is running true and not squealing.
Troubleshooting & FAQ
How do I know if this V-Belt fits my Yanmar engine?
This belt fits Yanmar 2YM15, 3YM20, and 3YM30 engines manufactured after June 2004 with a serial number before E20848. If your engine's serial number is E20848 or later, you require the flat serpentine belt (Yanmar part 128790-77580). Always check your engine plate or service manual to confirm compatibility.
What are the signs of a worn or failing alternator belt?
Common symptoms include a loud, high-pitched squealing sound from the engine bay, especially during startup or when the engine is under load. You might also notice visible signs of wear like cracks, glazing, or fraying on the belt surface. A failing belt can also cause a battery warning light to illuminate on your dashboard due to improper alternator charging.
How often should I replace the alternator belt?
There is no fixed replacement interval, as life depends heavily on engine hours, operating conditions, and belt tension. We recommend a visual inspection during every routine service. As a general guideline, consider replacing the belt every 3 to 5 years or if any signs of wear are evident.
Is this belt identical to the OEM Yanmar version?
This is a high-quality aftermarket part designed to function as a direct replacement for the OEM Yanmar 129612-42290E belt. It is manufactured to meet or exceed original equipment specifications for fit, durability, and performance, providing a reliable and cost-effective alternative.
Is this a genuine OEM part or an aftermarket replacement?
This listing is for a high-quality aftermarket replacement part, not an OEM component. It is engineered to meet or exceed OEM-level specifications using comparable materials. All our parts are manufactured in an ISO 9002 certified facility and are batch-inspected to ensure consistency and reliability.
How much is shipping and how fast will it arrive?
We ship worldwide, with most orders arriving within 5 to 15 days. Standard shipping is free on all orders. If you need the part sooner, expedited shipping options are available at checkout for most regions.
What is the warranty and return policy?
This product is covered by a 1-year warranty against any manufacturing defects under normal marine use. If you encounter any issues, please contact our support team with your order details for assistance. Unused items in their original condition can be returned within our standard return window; please see our full policy page or contact us 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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