Sierra Marine V-Belt 18-15550 | 55 in. / 139.7 cm × 29/64 in. / 11.5 mm
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Sierra Marine V-Belt 18-15550
Part Number: 18-15550 (Sierra) | UPC: 030999566744
The Sierra 18-15550 is a cogged marine V-belt for selected MerCruiser big-block inboard and sterndrive accessory-drive systems. High-strength synthetic cords resist stretching and shock loading, while the precision-moulded cog profile improves flexibility and allows cooling airflow around the belt. Rubber sidewalls maintain positive contact with pulley grooves throughout the service interval.
Belt Specifications
- Effective length: 55 in. / 139.7 cm
- Top width: 29/64 in. / 11.5 mm
- Construction: Cogged, synthetic-rubber
- Cord type: High-strength, low-stretch synthetic
- Profile: Moulded cog — improves flexibility and heat control
- Supplied as: Single belt
Compatible Applications
Cataloged specifically against the MerCruiser 57-13458 belt family — not a universal 7.4 L replacement. Confirmed applications:
- MerCruiser 330 / GM 454 CID / 7.4 L — 1982–1987
- MerCruiser 454 MAG Alpha / 7.4 L — 1986–1989
- Selected MerCruiser 454 MAG Bravo / 7.4 L Bravo — early 1990s accessory-drive configurations
Fitment Notice
MerCruiser 454 and 7.4 L engines were produced with different alternator, water-pump, and power-steering belt arrangements depending on production year, drive model, and pulley layout. Engine displacement alone is not sufficient to confirm fitment. Before ordering, verify:
- Engine model and production year
- Engine serial number
- Existing OEM belt number
- Accessory-drive and pulley configuration
- Required belt effective length and top width
OEM & Cross-Reference Part Numbers
- Sierra: 18-15550
- Mercury / MerCruiser: 57-13458
- Mercury / MerCruiser: 57-13458T
- Mercury / MerCruiser: 57-13458Q
- Mallory: 9-55000
Need a different length? See related belts in the same series:
- Sierra 18-15400 V-Belt
- Sierra 18-15410 Cogged V-Belt
- Sierra 18-15450 V-Belt
- Sierra 18-15455 V-Belt
- Sierra 18-15460 Cogged V-Belt
- Sierra 18-15470 Marine V-Belt — 47 in. / 119.4 cm
- Sierra 18-15480 Marine V-Belt — 48 in. / 121.9 cm
- Sierra 18-15520 Power Steering V-Belt — 52 in. / 132.1 cm
When to Replace the Belt
- Cracks visible between cogs or on belt edges
- Frayed or glazed belt surfaces
- Squealing or slipping under load
- Belt dust present around the pulleys
- Proper tension can no longer be maintained
- Oil or coolant contamination on the belt
- Belt riding unusually low in the pulley groove
Installation Notes
- Inspect all pulleys for wear, corrosion, and misalignment before installation
- Do not pry the belt over pulley flanges with sharp tools
- Confirm correct belt routing and accessory alignment
- Set tension to the engine manufacturer's specification
- Rotate the drive by hand to confirm the belt seats fully in each pulley groove
- Recheck tension after the initial operating period where specified
A belt failure on a MerCruiser big-block can simultaneously disable raw water cooling, power steering, and battery charging — consider carrying a spare onboard.
Related Parts
- Mercury MerCruiser Quicksilver Serpentine Belt 865615Q07
- Sierra Serpentine Belt — Marine Inboard — 47-15103
- Marine Alternator 12V 65A — Replaces MerCruiser 805447T
- Marine Alternator 12V 55A — Replaces MerCruiser 817119A1
- Volvo Penta Power Steering V-Belt 3858462
Parts Desk Insights
The Sierra 18-15550 is the go-to pre-season replacement for owners of MerCruiser 330 GM 454 (1982–1987) and 454 MAG Alpha (1986–1989) boats. The most reliable confirmation method is matching the original OEM belt number: if it cross-references to 57-13458, 57-13458T, or 57-13458Q, this belt is in the correct interchange family.
A common issue: customers order by engine displacement alone and receive the wrong belt. The 7.4 L / 454 family used several different accessory-drive layouts across model years and drive configurations. Always verify the OEM number and full pulley arrangement. Given the consequences of a belt failure at sea on a big-block — simultaneous loss of cooling, steering, and charging — keeping a spare onboard is strongly recommended for any extended cruise.
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 1-3 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.