| So you like performance boating – great! If you look around you and observe how many people experience valvetrain problems in their big block equipped performance boat, you might realize that this duty cycle is taxing on that system. In fact, an engine that spends 600 hours at an average speed of 5500rpm will rack up nearly 100 million high stress valvetrain cycles over its lifetime. This is higher than any racing, passenger car or light truck engine. Clearly, the valvetrain solution for offshore performance pleasure boats will be different than those for racing engines or passenger car engines. The main failure modes in offshore powerboats are found in rocker arms, valvesprings, lifters, valves and valve/valve seat recession. First, let’s discuss rocker arms. The industry standard in offshore powerboat engines are stud mount rocker arms with roller bearings pressed into aluminum extrusions. They are no doubt popular because they are cost-conscious and are perceived to be designed for high performance applications. Unfortunately, they are not a good fit for offshore performance. The first reason why is the mounting method. The mounting studs, while stiff in tension, are unfortunately not purely loaded in tension. The side loading of the rocker stud is a significant source of compliance (read: frequency reduction) which we don’t want. A system like the one described above will have you looking under your valve covers every 200 hours when you should be out on the water. While stud girdles can improve things somewhat, the best solution is a shaft-mounted system. Stay tuned for the next discussion, where we’ll dive into rocker arm materials. |
