The 8-piece Upper Motor Mount Bolt Kit from Buckshot Racing #77 is a direct-service hardware package for Mercury Marine and Mercury Racing V-6 outboards. It replaces the upper motor mount fasteners with OEM-spec bolts and stainless hardware that maintain clamping force, preserve alignment, and resist corrosion in harsh marine environments.
Designed for Mercury 2.0L, 2.4L, and 2.5L V-6 engines, this Upper Motor Mount Bolt Kit is ideal for bass boats, performance hulls, and jet applications where the upper mounts are constantly loaded by trim, steering, and rough-water impacts.
Hardware Specification
Each 8-piece kit is built around two (2) OEM Upper Motor Mount Bolts that match Mercury part number 78689. For catalog and search purposes these bolts cross-reference to 8M0000491, 10-78689, and 8M0176309. They are dimensionally correct for factory upper motor mount saddles, providing the proper shank length and thread engagement through the Mercury V-6 midsection and bracket.
The bolts are paired with two (2) Stainless Mil Spec Flat Washers that correspond to Mercury OEM part number 78688. These washers provide the correct bearing surface beneath the bolt heads, spreading the load across the aluminum mount brackets and reducing the risk of fretting, galling, or distortion under repeated torque cycles.
To lock the assembly in place, the kit includes two (2) Stainless Lock Washers and two (2) Stainless Nylock Nuts that replace Mercury OEM part number 34933.
The combination of mechanical lock washer and nylon-insert locking nut provides excellent resistance to loosening from engine vibration, steering input, and transom flex.
Together, the OEM-spec bolts 78689, stainless Mil Spec washers 78688, stainless lock washers, and stainless Nylock nuts 34933 form a complete upper motor mount hardware stack.
Fitment: Mercury Marine and Mercury Racing 2.0L, 2.4L, 2.5L V-6 Outboards
This Buckshot Racing upper motor mount hardware kit is intended for Mercury V-6 platforms that specify bolt 78689 or its cross-reference numbers 8M0000491, 10-78689, or 8M0176309 in the factory parts book. That group covers a wide range of popular 2.0-liter, 2.4-liter, and 2.5-liter Mercury outboards, including many V-135, V-150, V-175, and V-200 models, along with numerous V-220 Laser and XRi outboards.
The same upper mount architecture is commonly used on performance variants such as XR2, XR4, XR6 Magnum, and many Pro Max and Super Mag 150/200/225 EFI engines, as well as 245 HP carb, 260 EFI, and 280 EFI long-shaft race and lake motors.
Several Mercury V-6 jet outboards—such as 105 Jet, 115 HP V-6, 135 HP V-6, and 140 Jet variants—also specify the same upper motor mount bolt family and are candidates for this kit. Whenever a Mercury upper mount parts diagram lists 78689 or its cross references, this Buckshot Racing #77 8-piece Upper Motor Mount Bolt Kit is engineered as the direct replacement.
Installation & Technical Notes
Installation of the upper motor mount bolt kit will be familiar to any technician experienced with Mercury V-6 midsections. The engine must first be supported securely on a hoist or transom stand so that the midsection and swivel bracket are not carrying the engine weight while the upper mount hardware is removed. Once access is established, the original upper motor mount bolts, washers, and nuts are removed and the mating surfaces inspected for corrosion, elongation, or cracking. Any damaged components should be addressed before reassembly.
The new OEM-spec bolts 78689 are then inserted through the upper motor mount brackets with the stainless Mil Spec flat washer 78688 positioned under each bolt head. The stainless lock washers are installed under the stainless Nylock nuts 34933 on the opposite side. A light application of marine-grade anti-seize on the bolt threads improves future serviceability without compromising the locking function of the Nylock insert.
Torque is brought up gradually and evenly from side to side, following the sequence and specifications published in the Mercury service manual for the specific 2.0L, 2.4L, or 2.5L V-6 model. Achieving correct torque is essential: it ensures proper compression of the upper mounts, controls engine movement on the swivel bracket, and maintains steering precision at high speed.
Under-torqued hardware can allow the powerhead to shift and pound the mounts; over-torqued hardware can crush the rubber or distort the brackets. The stainless washers and lock elements in this kit are selected to reproduce the factory clamp height and load path so the mounts behave as Mercury intended, while offering improved resistance to corrosion and loosening.
The Buckshot Racing #77 8-piece Upper Motor Mount Bolt Kit provides a complete, OEM-correct and stainless-enhanced replacement for Mercury upper motor mount hardware using bolt 78689 and its cross references 8M0000491, 10-78689, and 8M0176309, along with washer 78688 and Nylock nut 34933.
Designed for Mercury Marine and Mercury Racing 2.0L, 2.4L, and 2.5L V-6 outboards—including V-135, V-150, V-175, V-200, V-220 Laser, XR-series, Pro Max, Super Mag, and related jet models—this kit restores clamping integrity at the upper mounts and provides long-lasting corrosion resistance in demanding fresh and saltwater use.
For technical questions or application verification, contact Mike Hill at +1-714-697-1716 or mike@buckshotracing77.com.