In the grand scheme, an outboard motor’s drive system isn’t terribly complicated, especially when compared to something like an automobile’s. A boat drive system has two main functions: forward and reverse. Each of these is controlled by a cog that locks into place when the boat is put into gear. Forward, and the gear turns the propeller in one direction launching the boat through the water. Reverse, and it turns the propeller the other way, sending the boat backward. Different outboard motors have different parts that fit their boat drive systems, so it’s important to find the appropriate make and model when you’re planning to do repairs. It’s possible to buy specific parts, so if there’s one piece in particular that needs replacement, you can identify it and do that. Otherwise, if for a full rebuild or starting from scratch, then a full boat drive system replacement kit—which usually includes o-rings, bearings, gears, and may even include a full housing for the lower unit—will fit the need best. While they may be simple comparatively, boat drive systems still use a lot of parts that can wear out over time, meaning it’s likely to need service on occasion over the life of the outboard. Use our Marine Engine Parts Selector Tool to find the right engine parts for your boat.