57-48122Q Alternator Drive Belt for MerCruiser 5.7L 7.4L 8.2L | JLM Marine

Alternator Drive Belt for MerCruiser 5.7L 7.4L 8.2L Inboard Sterndrive Engines

This alternator drive belt is engineered for MerCruiser inboard sterndrive engines, including 5.7L, 7.4L, and 8.2L models from the late 1960s through 1997. It ensures reliable power delivery to your alternator, supporting a wide range of engine configurations from classic MIE models to modern MAG and EFI systems.

Direct replacement for OEM part numbers 57-48122, 57-48122Q, and Sierra 18-15480.

• 48-inch V-belt designed for alternator drive applications
• Compatible with multiple MerCruiser engine series including MAG, MIE, TRS, and MPI variants
• Fits engines ranging from 5.7L to 8.2L displacement

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below.

Technical Specifications

Package Contents

• 1 × 48" V-Belt

Installation Guide

1. Disconnect the battery negative terminal to ensure safety during installation.
2. Locate the alternator and identify the belt routing path around the pulleys. Take a photo if needed for reference.
3. Release tension on the old belt by loosening the alternator adjustment bolt or belt tensioner.
4. Remove the old belt from all pulleys, inspecting each pulley for wear or damage.
5. Route the new 48" V-belt around the pulleys following the original path.
6. Adjust the alternator position or tensioner to apply proper tension to the belt. The belt should deflect approximately 1/2 inch when pressed firmly at its midpoint.
7. Tighten the alternator mounting and adjustment bolts securely.
8. Rotate the engine by hand (or briefly bump the starter) to ensure the belt is seated correctly on all pulleys.
9. Reconnect the battery negative terminal.
10. Start the engine and verify proper alternator operation and belt tracking. Listen for any unusual noises.
11. Recheck belt tension after the first hour of operation and adjust if necessary.

Troubleshooting & FAQ

Q: How do I confirm this belt fits my MerCruiser engine?
A: Cross-reference your engine model and year in the Compatible Engine Models table above. You can also verify your OEM part number matches 57-48122, 57-48122Q, or Sierra 18-15480.

Q: How often should I replace the alternator drive belt?
A: Inspect the belt every season or every 100 hours of operation. Replace it if you notice cracking, glazing, fraying, or loss of tension. Typical service life ranges from 2–5 years depending on usage and conditions.

Q: What are the signs that my alternator belt is failing?
A: Common symptoms include squealing noises (especially during startup or acceleration), battery warning light activation, dimming lights, or visible belt damage such as cracks and fraying.

Q: Can I adjust the belt tension myself?
A: Yes. Loosen the alternator mounting bolts, adjust the alternator position until proper tension is achieved (approximately 1/2 inch deflection at the belt's midpoint), then retighten the bolts securely.

Q: Is this an OEM part or aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.