The Mercury 2.5-liter V6 outboard engine remains a legendary platform in high-performance marine racing, prized for its lightweight design and high-revving capability.
 
As builders push the limits of this two-stroke engine—especially in competitive drag, circuit, and offshore applications—upgrading the piston and ring package becomes a critical path to unlocking additional horsepower, reducing friction, and enhancing long-term durability.
 
One of the most effective upgrades in this area involves using Vertex V2400 Series Pistons, which feature an advanced crown design and a high-performance 1.5mm ring pack.
 
However, when these pistons are installed in engines using top-guided connecting rods, a specific adaptation is required to maintain proper wrist pin alignment and axial control. This is where the Wrist Pin Conversion Washer becomes an essential component.
 
In Mercury 2.5L V6 engines equipped with top-guided rods, lateral alignment of the piston is managed at the small end of the connecting rod rather than at the crankshaft's big end.
 
The factory top-guided rod and wrist pin interface is not compatible with the wrist pin boss geometry of the Vertex V2400 piston, which is designed for a narrower wrist pin span due to the thin-ring configuration.
 
Without proper axial control of the wrist pin, the pin can shift laterally during engine operation, leading to uneven wear, poor ring seal, piston skirt scuffing, and eventual ring land damage.
 
The Wrist Pin Conversion Washer, also referred to as a pin spacer or axial thrust washer, corrects this misalignment by occupying the lateral gap between the rod and the piston pin bosses, thereby stabilizing the wrist pin in the correct axial position.
 
Precision-machined from hardened tool steel, the washer is designed with exacting tolerances to maintain correct side clearance between the rod and piston—typically in the range of 0.002 to 0.005 inches.
 
This ensures full floating wrist pin functionality while preserving oil film integrity and minimizing the risk of pin galling. When installed correctly, the washer prevents any lateral migration of the pin and allows the piston to remain centered in the bore, even under high combustion pressures and thermal expansion.
 
The primary motivation for using the V2400 piston and 1.5mm ring combo is performance. Compared to standard 2mm ring sets, the 1.5mm configuration significantly reduces ring drag, improves conformability at high RPM, and enhances sealing characteristics under peak cylinder pressures.
 
Combined with the Vertex piston’s advanced skirt profile and alloy construction, this upgrade supports elevated engine speeds and better thermal management—key advantages in high-output, high-RPM racing environments. However, achieving this performance advantage in a Mercury 2.5L running top-guided rods is only possible when the wrist pin is properly located and stabilized using the conversion washer.
 
Installation requires careful measurement of rod width, piston pin bore spacing, and pin diameter. Builders must confirm total stack-up width and calculate the proper washer thickness to maintain OEM or target wrist pin side clearance.
 
During assembly, high-pressure assembly lubricant should be applied to the wrist pin and washer interface to ensure hydrodynamic separation during initial engine operation.
 
Includes one (1) Wrist Pin Conversion Washer, Vertex 1.5MM, Buy 12, Save $36
 
Contact Mike Hill at +1-714-697-1716 or email mike@buckshotracing77.com for technical support.