Mercury Quicksilver Double-Wound Split Lock Washer 13-33734 | MerCruiser Flywheel & Engine Mount Hardware

Double-Wound Split Lock Washer for MerCruiser Flywheel & Engine Mount Applications

The Mercury Quicksilver 13-33734 is an OEM heavy-duty double-wound split lock washer used in select MerCruiser sterndrive and inboard/outboard applications. The double-wound spring profile generates higher clamping force than a standard single-coil lock washer, making it the correct choice for high-vibration locations such as rear engine mounts, flywheel housings, and coupler hardware where fastener retention is critical.

At 1/2" inside diameter, this washer is sized for 1/2" fastener hardware. It should be replaced any time it is removed from a critical mounting location — a flattened or fatigued lock washer provides no meaningful resistance to vibration-induced loosening.

Part Information

• Part Number: 13-33734
• Short Reference: 33734
• Brand: Mercury / Quicksilver
• Official Product Type: Double-Wound Split Lock Washer
• Barcode / UPC: 0745061079199
• Supersedes: 33734A1, 33021
• Inside Diameter: 1/2" (nominal)
• Style: Double-wound / heavy-duty spring coil

Compatible Applications

• MerCruiser sterndrive rear engine mount hardware assemblies
• MerCruiser flywheel and flywheel housing fastener stacks
• MerCruiser coupler and transom plate mounting hardware
• Any MerCruiser inboard/outboard application where the parts diagram specifies part 13-33734 or 33734 in the hardware stack

Fitment Note: Verify by engine serial number, mount or flywheel diagram, and original hardware stack-up before ordering. Mounting hardware can vary by engine package, transom assembly, flywheel housing style, coupler type, and production range.

System & Diagram Position

This washer appears in the engine mount, flywheel, and coupler hardware sections of the MerCruiser parts diagram. It is part of the fastener stack — typically seated between the nut and the mounting surface or housing flange — where its spring tension resists loosening under engine vibration and torque load. Locate it in the diagram for your specific engine serial number range to confirm position and quantity required.

Dimensions

• Inside Diameter: 1/2" (nominal, for 1/2" fasteners)
• Style: Double-wound split lock washer (heavy-duty)
• Approximate Weight: 10 g (0.01 kg)

When to Replace

• Washer is flattened, cracked, distorted, or has lost spring tension
• Visible corrosion or pitting that compromises the seating surface
• Any time the fastener stack is disassembled at a critical mount or flywheel location
• Missing from the hardware stack during inspection or rebuild

Installation Notes

• Install in the exact position and orientation shown in the Mercury parts diagram for your engine
• Inspect related studs, nuts, mount pads, and coupler hardware for wear or corrosion before reassembly
• Do not reuse a flattened or fatigued lock washer — it will not provide adequate clamping retention
• Follow Mercury service manual torque specifications for the fastener location where this washer is used
• Confirm engine alignment after any rear mount or coupler hardware service

Related Parts

• Mercury MerCruiser Quicksilver Driveshaft Locknut 41527T
• Mercury Quicksilver Exhaust Manifold Gasket 27-33395
• Mercury Fuel Pump Gasket 27-34213

Technical FAQ

Q: What is the difference between a double-wound and a standard split lock washer?
A: A double-wound lock washer has two coils stacked together, which produces significantly higher spring force and clamping resistance than a single-coil washer. Mercury specifies the double-wound version in high-vibration locations like engine mounts and flywheel hardware where a standard lock washer would be insufficient.

Q: Can I substitute a standard 1/2" lock washer from a hardware store?
A: Not recommended for these applications. The double-wound specification exists because standard lock washers do not provide adequate retention in high-vibration marine engine mounting locations. Using the correct OEM part is the safest approach.

Q: How many of these washers does my engine require?
A: The quantity varies by engine package and mounting configuration. Check the Mercury parts diagram for your specific engine serial number to confirm the number of washers in the hardware stack at each location.

Q: Does 33021 cross-reference directly to 13-33734?
A: Yes — 33021 is listed as a superseded reference that 13-33734 replaces. If you have an older parts list showing 33021, 13-33734 is the current OEM part to order.

Parts Desk Insights

Best use case: This washer is the right call during any rear engine mount service, flywheel removal, or coupler hardware rebuild on a compatible MerCruiser. At this price, it should always be replaced rather than reused — a fatigued lock washer in a flywheel or mount stack is not worth the risk of a fastener working loose under load.

Common mistakes: The most frequent mistake is substituting a standard hardware-store lock washer because it looks similar. The double-wound specification is there for a reason — standard single-coil washers do not hold up the same way in these locations. A second common mistake is ordering only one when the diagram calls for multiple — always check the parts diagram for your serial number to confirm the quantity needed at each fastener location before ordering.