Sierra 18-55505 Replacement Starter Motor – Mercury Verado, Pro XS, SeaPro & FourStroke V6/V8 Outboards
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Sierra 18-55505 Replacement Starter Motor
Part Number: 18-55505 (distributor ref: 47-55505F1)
Brand: Sierra International
UPC: 808282379094
Product Overview
A complete replacement starter motor assembly for selected Mercury Verado, Pro XS, SeaPro, Racing, and FourStroke V6 and V8 outboards. Features an updated planetary gear and clutch spring design, improved solenoid construction, extended battery terminal for easier connection, and integrated sealing to reduce water intrusion. Designed for use with Sierra solenoid 18-6458.
Compatible Applications
- Mercury 175 HP 3.4L V6 FourStroke
- Mercury 200 / 225 / 250 / 300 HP 4.6L V8 Pro XS
- Mercury 225 / 250 / 300 HP 4.6L V8 SeaPro
- Mercury 250 / 300 HP Verado
- Selected Mercury 250 / 300 HP Racing V8 applications
Serial Number Note: Many 3.4L V6 and 4.6L V8 applications begin at serial number 2B529482 and up. Racing applications use separate serial ranges. Always confirm engine model, displacement, horsepower, and serial number before ordering — matching the existing OEM Mercury starter number is the most reliable fitment check.
OEM Cross-Reference Part Numbers
- Mercury: 50-8M0061073
- Mercury: 50-8M0080274
- Mercury: 50-8M0096343
- Mercury: 50-8M0137789
- Mercury: 50-8M0142679
- Mercury: 50-8M0187292
- Additional references: 8M0055425, 8M0055430, 8M0079328, 8M0099252
When to Replace
- Slow or intermittent cranking despite good battery voltage
- Starter fails to engage the flywheel
- Excessive starter noise or grinding
- Internal solenoid failure
- Complete no-start with confirmed power to the starter circuit
Installation Notes
- Disconnect battery power before beginning any starter service
- Inspect battery cables, ground connections, and solenoid wiring before installing the replacement
- Check flywheel ring gear engagement surfaces for wear
- Verify secure electrical connections and test cranking operation after installation
- Use with Sierra 18-6458 solenoid where applicable
Related Products
- Mercury MerCruiser Quicksilver Solenoid 8M0185622
- Arco 5381X Replacement Starter – Mercury/Mariner 150–225 HP
- ARCO 57-5381 Starter Motor – Mercury/Mariner 200–225 HP V6 DFI
- ARCO 57-5367 Outboard Starter – Mercury/Mariner 6–25 HP
- ARCO 57-5374 Outboard Starter – Mercury 65–85 HP 4-Cylinder
Parts Desk Insights
This starter spans several modern Mercury V6 and V8 outboard families — matching by horsepower alone is not sufficient. The safest fitment check is to look up the existing Mercury OEM starter part number on the engine and cross-reference it against the list above. The most common ordering issue is customers specifying only horsepower without the serial number, which leaves fitment uncertain across Verado, Pro XS, and SeaPro variants that share the same HP rating. Always ask for the serial number and existing starter PN before confirming the order.
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.