Motor Shaft Couplers, Brushes and Engine Locks

Shaft couplers and bearings: bore, length and alignment

A shaft coupler joins two shafts, so its two bore sizes must match the shafts, as in a 5 mm to 8 mm coupler. Rigid couplers transmit power with no give and need accurate alignment, while flexible ones take up small misalignment. Set screws must seat on a flat if the shaft has one. Flange bearings carry a shaft in a bracket; the bore, outside diameter and width define the fit, and a self-aligning type tolerates a little tilt. Ground shafts and rods are specified by diameter, length and tolerance.

Carbon brushes, shafts and locks: dimensions and fit

Carbon brushes wear down and should be replaced in pairs, with the same grade and the exact size. Brush sizes list three dimensions in an order that differs between makers, so measure the worn brush and compare each one, and check that the spring and holder suit the new brush. Stainless steel rods resist corrosion in a damp boat but are softer than hardened ground shafts. A sterndrive theft lock is made for one drive model, so match the model before buying.

Questions about Motor Shaft Couplers, Brushes and Engine Locks

How do I measure a motor shaft coupler?

Measure the diameter of each shaft with calipers and choose a coupler with those two bore sizes, such as 5 mm and 8 mm. Then check its length and outside diameter against the space, and whether the set screws can reach the shafts.

When should carbon brushes be replaced?

Replace them when they are worn close to the minimum length marked by the motor maker, when they chip, or when the motor sparks heavily or loses power. Swap both brushes of a pair together and check the commutator surface.

Is stainless steel shaft stock as strong as hardened steel?

Not usually. Stainless resists rust, which helps in damp or salty air, but common stainless grades are softer and wear faster than hardened, ground steel shafts. Choose stainless for corrosion resistance and hardened steel for bearing surfaces under load.