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diagnose a
Spun
Propeller Hub
fix a spun
propeller hub
A spun propeller hub can ruin your day
The lowly propeller that provides forward motion. At least
until bad things happen to a good propeller. You’d think the punishment
propellers endure when they whack into an inanimate object would be a
death sentence. But even when a spun hub spins, or a blade curls back at a
sickening angle the damage usually be remedied and for less money than you
may think.
Another culprit is fouling the propeller with someone's abandoned
dock line. When it wraps around the prop the engine keeps turning. What
happens next isn't pretty.
Depending on the size of the wheel and the extent of the damage
inflicted a propeller can be reconditioned for as little as 30 to 100
dollars.
Step one is to determine whether a hub is spinning in its
bore, and incapable of transferring engine energy into forward motion.
Find out in minutes by removing the propeller and peening a dot both in
the hub and the mating propeller surface. Use a hammer and a center punch.
Next re-install the propeller and run the engine under load.
Remove the propeller again and look at your handiwork. If the dots
no longer line up, the rubber hub is spinning in its bore.
More obvious symptoms are melted rubber, where the hub has begun to
disintegrate.
So how to you replace a spun hub? Simple. Prop shop
techs use a hydraulic ram and many tons of pressure to unceremoniously
press the bad hub out of of its bore. It’s tossed in the trash heap. A new
one is pressed in, carefully. To ease the interference fit it’s liberally
lubricated with spray of soap and water
Some new wave propellers
dispense entirely with the venerable fixed hub system. In its place are
replaceable hubs with a different hub available to fit each one of the
spline patterns required for the different brands of outboard motors and
stern drives. In the unlikely event a hub is ever damaged simple take off
the wheel, lift out the wrecked hub and throw it in the trash bin. Insert
a new hub and you are back in the waster in matter of minutes
Beyond quick fixes, what’s really nice about the system is the way
you can switch from one pitch propeller to another so speedily That’s
invaluable for a boat that pulls double duty as a fast flyer or a ski tow
boat.
Straightening bent blades is a very delicate matter. Savvy
prop techs never use force. Instead, they reach for a bigger hammer. To
reform the blade to its original profile, the wheel is placed on mandrel,
which is just another name for a fancy shaped blacksmith’s anvil. Each
mandrel is calibrated to shape a different pitch. Sometimes the blades are
heated before hammering because softer metal is malleable and returns to
shape without stressing the metal.
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