Problems associated with the bellows are related to fatigue, mechanical abuse, or improper installation.īellows fatigue can occur as the bellows material deteriorates over time. Second, it acts as a spring, pushing the flange against the rotor. First, it creates a watertight barrier between the stern tube and the interior of the boat. The key to preventing setscrew and rotor movement problems is to place a hose clamp on the prop shaft up against the forward face of the rotor, so that even if the rotor works loose, the hose clamp will prevent the rotor from moving away from the flange. So, when the bellows finally returns to its natural, relaxed position, a tiny space is left between the flange and rotor. According to one manufacturer’s instructions, the setscrews are never to be reused, and a new set of screws should be used each time the rotor is installed.Īnother issue with a spinning rotor is that the flange and rotor are so well mated that there is a suction effect between them, and the rotor can actually stretch the bellows beyond its relaxed position before the seal is broken. It happens more often than you might think. Once the bellows are relaxed, the mechanical seal between the rotor and flange is lost, and sea water can flow into the bilge. If the screws lose their grip, the bellows can slowly push the rotor forward on the prop shaft. Some dripless shaft seal products use set screws to hold the rotor in place. Dripless seals are popular because they don’t require adjustment after installation and they continue to keep sea water out even if the drive train is out of alignment, producing a dry bilge and creating a safer, cleaner, more corrosion-resistant and sweeter smelling vessel.
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