The Mercury Flywheel Nut (OEM part numbers 52901 and 11-52901) and Flywheel Washer (OEM part numbers 33001, 68229, 12-68229, and 12-33001) are the standard clamping hardware used across Mercury, Mariner, and Mercury Racing legacy V-6 two-stroke engines. The crankshaft-to-flywheel taper interface is crucial across the 2.0L, 2.4L, and 2.5-Liter outboards and Sportjets, so the hardware that establishes preload on that taper remained the same.
 
What the Nut & Washer Kit Fits
This same nut and washer apply to the broad production ranges often labeled V-135, V-140, V-150, V-175, and V-200, including XR-2, XR-4, and XR-6 variants. They also apply to the performance and racing engines: 225 Pro Max and Super Mag, 260 EFI in all configurations, 280 ROS, SST-120, and S3000. SportJet V-6 units—175, 200, 210, and 240—50, 60, 70, 75, 90 HP (3, 4, and 6 cylinders) use the same upper crank snout and therefore the same flywheel nut and case-hardened washer.
 
Why This Hardware Matters
The proper clamp load from the mil-spec Cadmium-Plated Nut and Case-Hardened Washer prevents micro-motion at the interface, which would otherwise present as scatter in ignition timing or worse yet stress on the crankshaft.  The unchanged part numbers reflect this engineering priority: a consistent taper and a consistent clamping system reduce variables in a critical reference joint.
 
Torque Specs
Mercury service literature specifies a flywheel nut torque of 90-115 ft-lb for standard applications. Applying torque to a clean, dry taper and hardware at room temperature is standard practice; lubricants are not specified for the taper.
 
After torque, many techs place an alignment witness mark across the nut, flywheel, and a fixed reference so that any relative movement during service can be seen at a glance. It is a straightforward way to confirm that the taper preload is holding under operating torsion.
 
FAA-style Nylock Guidance
The nut is a nylon-insert locking fastener. FAA guidance (as echoed in general industry practice) treats nylock reusability as condition-based, not cycle-based. The nylon insert must provide measurable locking drag after first thread engagement; if the nut can be spun on by fingers with little or no resistance once engaged, the locking function has been lost and the part is unserviceable.
 
Nylock hardware that has been heat-soaked repeatedly or removed and installed enough times to diminish nylon drag should be replaced rather than rationalized into one more use.
 
Motor Model Fitment
If the engine tag or catalog says 260 EFI, 280 ROS, SST-120, S3000, 225 Pro Max, Super Mag, V-150, V-175, or V-200—and it’s a legacy two-stroke V-6—the correct hardware is still the OEM Mercury flywheel nut (52901 / 11-52901) and flywheel washer (33001 / 12-33001). The two-digit prefixes are Mercury’s service format; they do not indicate a change to geometry or function.
 
The flywheel nut and washer identified as Mercury 52901 / 11-52901 and 68229, 12-68229 / 33001 / 12-33001 are the original, correct parts for clamping the unchanged V-6 two-stroke crank taper across 2.0L, 2.4L, and 2.5L engines, including 260 EFI, 280 ROS, and SST-120. Use the 90–100 ft-lb torque band on a clean, dry taper, verify with a witness mark, and apply the straightforward FAA-style condition rule for nylock serviceability. 
 
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.