Alternator Belt for Yanmar 2YM20, 3YM20 and 3YM30 – Replaces 129612-42290E and 25152-003800
Alternator Belt for Yanmar 2YM20, 3YM20 and 3YM30 – Replaces 129612-42290E and 25152-003800 is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
Alternator Belt for Yanmar 2YM20, 3YM20 and 3YM30 – Replaces 129612...
Alternator Belt for Yanmar 2YM20, 3YM20 and 3YM30 – Replaces 129612-42290E and 25152-003800 is backordered and will ship as soon as it is back in stock.
Product Details
This replacement Alternator Belt is intended for selected Yanmar Marine Inboard diesel engines. The company fitment record lists the Yanmar 2YM20, 3YM20 and 3YM30 models.
This is a single replacement belt for the alternator drive system. It is identified with the Yanmar reference numbers 129612-42290E and 25152-003800. Confirm the part number and belt profile against the belt currently installed on your engine before ordering.
- Installation method: Replacement belt for the alternator drive
- Application: Yanmar Marine Inboard engines
- Product format: One belt; not a kit
- Fitment listed by the manufacturer: 2YM20, 3YM20 and 3YM30
Part Number Matrix
The following manufacturer reference numbers are associated with this replacement alternator belt.
| Brand | Reference Number | Application | Notes |
|---|---|---|---|
| Yanmar | 129612-42290E | Alternator belt | Reference number listed for this product |
| Yanmar | 25152-003800 | Alternator belt | Additional reference number listed for this product |
Engine & Model Compatibility
Use the model information below as a starting point for fitment verification. Engine variants and installed belt arrangements can vary, so compare the reference number and physical belt profile before installation.
| Brand | Model | Engine Type | Application | Reference Numbers |
|---|---|---|---|---|
| Yanmar Marine Inboard | 2YM20 | Marine diesel | Alternator belt | 129612-42290E; 25152-003800 |
| Yanmar Marine Inboard | 3YM20 | Marine diesel | Alternator belt | 129612-42290E; 25152-003800 |
| Yanmar Marine Inboard | 3YM30 | Marine diesel | Alternator belt | 129612-42290E; 25152-003800 |
Technical Specs
- Product type
- Alternator belt
- Product format
- Single replacement belt
- Application
- Yanmar Marine Inboard alternator drive
- Compatible models
- Yanmar 2YM20, 3YM20 and 3YM30
- Reference numbers
- 129612-42290E and 25152-003800
- Material
- Not specified in the manufacturer product record
- Dimensions
- Verify the installed belt profile and dimensions before ordering
What’s in the Box
- 1 x Alternator belt
Installation Notes
- Switch off the engine and disconnect the battery or main electrical supply before beginning work.
- Allow the engine to cool, then locate the alternator and belt adjustment hardware.
- Loosen the alternator pivot and adjustment fasteners only as much as necessary to release belt tension.
- Move the alternator toward the engine and remove the existing belt from the pulleys.
- Compare the replacement belt with the removed belt and confirm that the profile and length are appropriate.
- Install the replacement belt, making sure it is fully seated in every pulley groove.
- Adjust the alternator to obtain the belt tension specified by the engine manufacturer. Do not overtighten, as excessive tension can damage bearings.
- Tighten the pivot and adjustment fasteners securely.
- Reconnect the battery, start the engine, and check that the belt tracks correctly without abnormal noise or slipping.
Refer to the engine service manual for the exact belt-tension specification and fastener torque values.
Troubleshooting & FAQ
Which Yanmar engines are listed for this belt?
The manufacturer product record lists the Yanmar Marine Inboard 2YM20, 3YM20 and 3YM30 models. Verify the engine model plate and the reference number on the existing belt before ordering.
Which reference numbers are associated with this belt?
The listed Yanmar reference numbers are 129612-42290E and 25152-003800.
Is this a complete belt kit?
No. This listing is for one replacement alternator belt. It does not include an alternator, pulley, tensioner, fasteners or other accessories.
How do I know whether my existing belt needs replacement?
Inspect the belt for cracking, fraying, glazing, contamination, stretching or abnormal wear. Squealing, belt slip, charging problems or visible tracking issues can also indicate a belt or tensioning problem. Investigate the underlying cause before fitting a new belt.
What should I verify before ordering?
Confirm that your engine is a Yanmar 2YM20, 3YM20 or 3YM30, compare the existing belt with the listed reference numbers, and check the belt profile and dimensions. If the model or belt arrangement differs, consult the engine service manual or a qualified marine technician.
Is this a genuine Yanmar belt?
This listing is for a replacement belt associated with the listed Yanmar reference numbers. The product record does not identify it as a genuine Yanmar-branded component.
What warranty is included?
Warranty coverage is subject to the applicable seller terms. Please review the current order and returns information before purchase.
Safety & Important Information
- Disconnect electrical power and keep hands, tools and clothing clear of moving components during installation.
- Do not install a belt with a visibly incorrect profile, length or fit.
- Use the engine manufacturer’s service instructions for belt tension and fastener torque.
- Professional installation is recommended if the belt drive, alternator alignment or tensioning system is damaged or difficult to access.
About Sea Sierra
- Marine-Focused Parts — Replacement components selected for marine engine applications.
- Fitment Information — Product references and model applications are provided to help with part identification.
- Customer Support — Contact support with your engine model and existing belt reference if you need help confirming compatibility.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
