Corroded, rusted, or damaged cylinder head bolts are a common issue on aging Mercury V6 outboards. Whether you're rebuilding a classic XR4, refreshing a Pro Max, or assembling a Mercury Racing 260 EFI, quality cylinder-head hardware is essential for maintaining proper clamping force, sealing reliability, and long-term durability.
The Buckshot Racing #77 Mercury V6 Head Bolt Kit provides a complete replacement solution for Mercury 2.0L, 2.4L, and 2.5L two-stroke V6 engines. Each kit includes 24 flange-head cylinder head bolts and 24 extra-thick case-hardened Grade 8 gold zinc washers, providing everything needed for a complete cylinder-head installation.
Unlike factory hardware that is often heavily corroded after years of marine use, these kits provide improved corrosion resistance, enhanced appearance, and dependable clamping performance for both recreational and high-performance applications.
Built for Strength and Reliability
The Buckshot Racing #77 Grade 8 hardware options utilize high-strength flange-head bolts manufactured to approximately 150,000 PSI tensile strength. The gold zinc finish provides excellent corrosion resistance while delivering a clean, professional appearance.
The flange-head design helps distribute clamping loads more evenly across the cylinder head surface, while the included hardened washers provide an additional bearing surface that improves torque consistency and helps prevent washer distortion during installation.
Each kit includes 24 extra-thick case-hardened Grade 8 gold zinc washers measuring approximately 0.410" ID x 0.809" OD x 0.115" thick. These washers are particularly beneficial on fly-cut heads and high-compression applications where additional clearance and load distribution are desirable.
Three Fitment Options Available
Because Mercury utilized both gasket-head and O-ring-head cylinder configurations, Buckshot Racing #77 offers three versions of this kit.
Option 1 — Gasket Head Kit (Grade 8 Gold Zinc)
Designed for Mercury V6 engines utilizing conventional head gaskets, this kit includes the shorter 10-98534-style flange-head bolts and 24 extra-thick hardened washers. This configuration fits most production 2.0L, 2.4L, and 2.5L gasket-head engines.
Option 2 — O-Ring Head Kit (Grade 8 Gold Zinc)
Designed for Mercury O-ring cylinder heads, this kit includes the longer 8M0125882, 849677, and 10-878217-style flange-head bolts along with the same hardened washer package. The longer bolt length accommodates the deeper O-ring head configuration commonly found on Mercury Racing and high-performance engines.
Option 3 — O-Ring Head Kit (Mercury OEM Bolts)
This version fits the same O-ring-head applications as Option 2 but utilizes Mercury OEM galvanized flange-head bolts rather than aftermarket Grade 8 gold zinc hardware. The kit still includes the upgraded 24 extra-thick case-hardened Grade 8 gold zinc washers, providing improved load distribution, torque consistency.
This option is ideal for owners who prefer Mercury factory hardware while still benefiting from the upgraded washer package.
Broad Mercury V6 Fitment
These kits fit most Mercury and Mariner 2.0L, 2.4L, and 2.5L V6 two-stroke outboards produced between 1976 and 2005.
Common applications include the XR2, XR4, XR6, XRi EFI, Laser EFI, 150 HP, 175 HP, 200 HP, 220 Laser EFI, 225 HP, 225 Pro Max, Bridgeport, 245 Carb, 260 EFI, 280 ROS, 300 Drag, S3000, Formula 1, SST-120, SST-140, and numerous Mercury Racing, offshore, drag racing, and lake-race builds.
Because many engines have been modified over the years, cylinder-head style should always be verified before ordering.
Cross Reference Information
These kits cross-reference Mercury part numbers 10-98534, 8M0125882, 849677, 878217, 10-878217, and washer part number 12-25909.
Purchasing equivalent Mercury hardware individually can exceed $249 MSRP, making this complete 48-piece kit a cost-effective solution for engine rebuilds, cylinder-head upgrades, and routine maintenance.
Installation Notes
Proper cylinder-head installation is critical to achieving a reliable seal. Cylinder-head and block mating surfaces should be thoroughly cleaned before assembly, and new gaskets or O-rings should always be installed.
Lightly lubricating the bolt threads and washer surfaces helps ensure accurate torque readings. Bolts should be tightened using Mercury's recommended center-out crisscross torque sequence and brought to final torque in multiple stages according to the service manual specifications for the engine being serviced.
After initial heat cycling and operating time, many experienced engine builders recommend verifying final torque values to ensure uniform clamping force across all cylinders.
Final Thoughts from Buckshot Racing #77
The Buckshot Racing #77 Mercury V6 Head Bolt Kit provides a complete, professional-grade solution for restoring or upgrading cylinder-head hardware on Mercury's legendary 2.0L, 2.4L, and 2.5L two-stroke engines.
With your choice of Grade 8 gold zinc hardware or Mercury OEM galvanized bolts, plus upgraded case-hardened washers included in every kit, these packages deliver the strength, corrosion resistance, appearance, and reliability demanded by Mercury enthusiasts and racers alike.
For any questions or additional assistance, contact Mike Hill at 714-697-1716 or mike@buckshotracing77.com. Upgrade your Mercury outboard today with the reliability and strength of our premium Head Bolt Kit!