The belts that drive your engine’s accessories, the raw water pump, circulator pump and alternator, will typically provide reliable trouble-free service, provided they are properly maintained and replaced when worn out.Many cruisers neglect this all too important component, however, waiting until disaster strikes.Once the belt breaks, all of these vital systems grind to a halt, literally.The raw water pump stops pumping seawater, the circulator pumps stops circulating coolant and the alternator no longer produces electricity.While you may not immediately notice the loss of an alternator, you will very quickly become aware of the loss of seawater and coolant as the temperature gauge climbs into the red and the overheat alarm sounds (your engine is equipped with operating versions of both of these instruments, right?).The belts used to power these accessories are usually of the “V” variety; although the ribbon shaped flat serpentine belts are making inroads from large marine diesels to the smaller sailing auxiliaries.Often, one V belt may do double duty, sending power from the crankshaft pulley to both the alternator and circulator pump, while another belt will help the raw water pump do its thing.One serpentine belt, on the other hand, will typically operate all accessories.
Ordinary V belts are, with a little knowledge, easily serviced, adjusted and replaced.Just to give you an idea of the energy that a belt may be called upon to transmit, a high output alternator of 125 amps will require, after allowances are made for friction and electrical inefficiencies, roughly five or six horsepower, all of which is carried by the belt or belts.Generally speaking, conservative installations will resort to double belts when amperage exceeds 100 amps.
Begin by inspecting your engine’s belts.I’m often asked, “how tight should my belt be?”Without a tool for measuring this, that’s subjective question, however, the answer simply is, “tight enough so they don’t slip, but no tighter”.If a belt is slipping it won’t turn its related accessory properly and it will wear out and break prematurely.If it’s too tight, it will accelerate wear on bearings and seals.If you see any evidence of belt dust on the front of the engine or the alternator casing and fan, it’s so fine and “oily” that it’s often mistaken for an oil leak, then the belt is either slipping or misaligned. If the belt and/or pulley show signs of glazing, a particularly smooth, shiny appearance, it means the belt is slipping.A glazed belt must be replaced, but the glaze on a pulley can be broken or “dressed” using 220 grit sandpaper.
To tension an alternator, refrigeration compressor or water pump belt, use the handle of a hammer as a lever to pry the accessory away from the crankshaft pulley, then tighten the fixing bolt.Threaded “spreader” tools are available to make this task easier and some aftermarket high output alternator installations incorporate this into their design.Finally, ensure that each belt’s profile properly matches every pulley over which it turns.The belt should be even with or stand slightly proud, no more than a sixteenth of an inch, of the top of the pulley walls.
Belts are comparatively inexpensive, so it’s cheap insurance to replace them every 2 years or every 400 hours, whichever comes first.Remember, a new belt may require adjustment and retensioning several times in the first 50-100 hours of use.