If you’re rebuilding, resealing, or refreshing a Mercury 3-Liter 2-Stroke or Optima V6 outboard, the last thing you want is mismatched or tired hardware on aluminum cast cylinder heads.
Our 40-piece Metric Cylinder Head Bolt Kit is built for owners who want to replace their head bolts in one shot with consistent, corrosion-resistant fasteners. This kit includes 40 pieces of high-quality A2-70 stainless steel flange bolts, intended to replace applications where your parts diagram calls for Mercury OEM bolt numbers 859096, 891570050, or 8M0045380.
Mercury owners often search by horsepower and platform names, so you’ll commonly see this kit associated with terms like Mercury 300, 300 Pro Max, 3.0 Liter, 3.2 Liter, and 3.2 Liter Stroker builds. The most accurate way to confirm compatibility is still the OEM cross-reference—if your engine’s parts list references one of the bolt numbers above, this kit is designed for that use.
Why Flange Bolts Are a Smart Choice for Aluminum Cast Heads
Aluminum cast cylinder heads depend on even clamping to keep gaskets sealed and surfaces protected. A flange bolt is designed with an integrated flange under the head that helps distribute load over a broader area. That wider contact footprint helps reduce point-loading into aluminum castings and supports more consistent clamp behavior during torque steps and heat cycles—exactly what you want on a hard-working 2-stroke or high-output outboard.
A2-70 Stainless Steel: Strength + Corrosion Resistance for Marine Environments
This kit uses Grade A2-70 stainless steel, selected because it offers solid fastener strength and good corrosion resistance in many environments. On outboards, hardware is constantly exposed to moisture, salt air, rinsing chemicals, and repeated heat cycling. Stainless helps fight the rust and surface scaling that can seize bolts over time, making future service easier and helping your engine stay maintainable—especially when you actually use it the way it was built to be used.
This head bolt kit is commonly searched alongside Mercury V6 platform terms such as 200 HP 6 CYL (3.0L), 225 HP 6 CYL (3.0L), 250 HP XS (3.0L), 225 Pro XS (3.0L), 250 Pro XS (3.0L), and DTS 3.0L variants. It’s also frequently tied to higher-output searches like Mercury 300, 300 Pro Max, and 300 HP XS (3.2L), including performance builds described as a 3.2 Liter Stroker.
Because engines are often swapped or modified over the years, the correct way to confirm fitment is by verifying that your parts diagram or removed hardware cross-references 859096, 891570050, or 8M0045380.
Why a 40-Piece Kit Makes Sense
A 40-piece kit is ideal when you want consistent hardware across your cylinder head service instead of replacing “a few bolts” and hoping the rest behave the same. Using the same material, head style, and flange footprint across the job helps keep assembly uniform and simplifies your build—especially when you’re working through a reseal, rebuild, or offseason refresh and want to eliminate preventable problems.
If you’ve ever had a head bolt fight you during removal, or you’ve dealt with mixed hardware from past owners, a complete kit is the clean fix that puts you back in control.
Installation Notes (Do It Once, Do It Right)
Always follow the Mercury factory service manual for your exact engine and year. Proper results depend on clean threads, the correct tightening sequence, and correct torque steps. Aluminum cast heads are sensitive to uneven tightening, and gaskets don’t forgive shortcuts. Prep carefully, torque in stages, and verify your procedure for your specific Mercury V6.
This 40-piece Metric Cylinder Head Bolt Kit replaces Mercury OEM bolts commonly listed as: 859096, 891570050, and 8M0045380.
If you’re building or servicing a Mercury 3.0 Liter or 3.2 Liter V6 and want stainless flange bolts that are designed to distribute load properly on aluminum cast heads, this 40-piece head bolt kit is the right way to reset your hardware and move forward with confidence.
Contact Mike at 714-697-1716 or mike@buckshotracing77.com for technical support.