Mercury 2.0L Bottom Guided Pistons for 135 HP, 150 HP & XR2 Outboards (1976–1989)
 
The WSM SST-120 Piston Kits from Buckshot Racing #77 are high-quality replacement pistons designed for Mercury and Mariner 2.0 Liter V6 bottom-guided outboards. Built for durability, reliability, and proper OEM-style fitment, these piston kits are ideal for rebuilding classic Mercury fishing motors from the golden era of 2-stroke performance.
 
These pistons fit a wide range of Mercury XR2 and Mariner 135 HP and 150 HP bottom-guided engines manufactured from 1976 through 1988, making them an excellent solution for restorations, stock rebuilds, and dependable lake-performance applications. Available bore sizes include:
 
Standard bore
.010 oversize
.015 oversize
.020 oversize
.030 oversize
.040 oversize
 
This range allows engine builders and machinists to correctly match piston size to cylinder condition after boring and honing operations.
 
Designed for Mercury 2.0L Bottom-Guided Engines
 
The WSM SST-120 piston kits are specifically engineered for the early bottom-guided Mercury V6 architecture used in many 2.0-liter fishing motors. In bottom-guided designs, the connecting rod is centered by the crankshaft journal rather than the piston itself, making proper piston dimensions and skirt geometry critical for long-term reliability.
 
These engines became well known for their lightweight rotating assembly, strong midrange power, and high-RPM capability, forming the foundation for many later Mercury high-performance platforms.
 
The SST-120 pistons are designed to maintain proper fitment, ring seal, and piston stability while operating under the demanding conditions common to marine 2-stroke engines.
 
OEM Fitment and Cross-Reference Compatibility
 
These piston kits are direct replacements for several Mercury OEM piston assemblies and cross-reference to multiple factory part numbers commonly associated with 2.0L V6 bottom-guided engines.
 
Cross-reference numbers include: 7055A3, 7442A36, 7442A9, 765-6309A3, 765-6520A3, 765-7227A3, 765-7442A3, 765-7442T36, 765-7448A3
 
This broad interchangeability makes the SST-120 kit an excellent option for replacing worn, damaged, or obsolete factory pistons during rebuilds.
 
Built for Marine Reliability
 
Marine engines operate under constant load and high thermal stress, especially in 2-stroke applications where lubrication depends entirely on the fuel/oil mixture. Proper piston design is critical to maintaining ring seal, reducing friction, and controlling heat expansion.
 
The SST-120 piston kits are designed with these demands in mind, providing stable operation across a wide RPM range while maintaining the durability needed for long-term use in fishing, recreational, and mild performance applications.
 
When paired with proper machine work, ring end gap setup, and correct break-in procedures, these pistons provide dependable service life and strong overall engine performance.
 
Importance of Proper Bore Sizing
 
Selecting the correct oversize piston is one of the most important parts of a rebuild. Cylinder walls that are worn, scored, or out-of-round must be bored to the next appropriate size to restore proper clearance and ring seal.
 
The SST-120 kits are available in multiple oversizes to support this process, allowing machinists to clean up damaged cylinders while maintaining proper piston-to-wall clearance. Contact Mike to discuss your build.
 
Applications Across Mercury & Mariner Platforms
 
They fit many standard-port 2.0L bottom-guided fishing motors produced between 1976 and 1988 and remain a popular choice for restoring classic Mercury V6 engines still running strong today. These pistons are commonly used in: Mercury 135 HP V6 outboards, Mercury XR2, 150 HP V6 outboards, Mariner 135 HP engines, and Mariner 150 HP engines.
 
Why Bottom-Guided Mercury Engines Matter
 
The early Mercury bottom-guided V6 engines helped establish Mercury’s reputation for lightweight, high-revving outboard performance. Many enthusiasts still seek out these engines because of their responsiveness, simplicity, and strong aftermarket support.
 
A properly rebuilt 2.0L Mercury remains a capable and enjoyable platform for fishing boats, lightweight performance hulls, and classic restorations.
 
The SST-120 Piston Kits provide a reliable, OEM-style replacement solution for classic Mercury and Mariner 2.0L V6 bottom-guided engines. With availability in standard and multiple oversizes, these pistons support accurate rebuilds across a wide range of applications.
 
Whether you are restoring a vintage 150 HP fishing motor or rebuilding a classic Mercury V6 for years of continued use, the SST-120 kits deliver the fitment, durability, and performance required for a proper rebuild.
 
At Buckshot Racing #77, we continue to support the legendary Mercury 2-stroke platform with quality parts, technical knowledge, and real-world experience.
 
Contact Mike with any tech questions at 714-697-1716