Ignition timing on four-stroke outboards is critical to engine performance such that fuel charges and ignition spark are delivered precisely to match pistons reaching top dead center as they travel within the cylinder bores. This is accomplished with either chains or belts connecting the camshaft to the crankshaft, located under the powerhead or on top of the engine. Belts are serious business, and if you are a Yamaha four-stroke owner, this article is for you.
Annual service allows a shop technician to inspect engine components regularly, during which time many problems can be avoided. The timing belt, pulleys, and tensioner are critical in Yamaha engines as they are engineered with what is known as interference fit. If the belt breaks, the valves will interfere with the pistons causing severe damage. When running the outboard, any unusual sound can be a signal of pulley or tensioner fatigue. Tiny black fibers found under the cowling are usually telltale signs of belt wear.
The timing belt replacement interval is five years or 1000 hours of operation. The pulleys can develop cracks and the tensioner inspection involves rolling the bearings to check for smoothness. The assessment does not take much time and can save money in the long run as well as downtime. The presence of oil or an oily film indicates an existing problem at the crankshaft oil seal.
Have a great late summer boating and fishing season!
Coastal Bend Marine – Port O’Connor, TX
coastalbendmarine.com – 361-983-4841