I have a A O Smith SN 1152 pool pump. The motor just hums when the switch is turned on. The pump is eight years old and I have had no problems until now.

voltage set right? motors come set from factory 240 v .. or you might have moved the start switch, it's at 6 0clock on the motor make sure its centered (back of the motor) shaped like a v.. looks like this.click on this
also might be a bad start or run capacitor..or a dud motor
hope this helps
jay the pool pump motor repair guy in longwood Florida

DIRTY START switch or the motor is locked up, breaker off ! remove motor from tank body and see if the motor will turn over if it does could be the switch or the motor is shorted witch there is no fix but a new or rebuilt motor. search your area for your local pool pump motor repair guy with free testing..
Jay the pool pump motor repair guy longwood Fl

3 THINGS QUICK.. RUN CAPACITOR THIS IS LOCATED ON TOP OF MOTOR HAVE IT CHECKED. OR START SWITCH DIRTY OR STAR CAPACITOR BAD.. SEARCH YOUR AREA FOR YOUR LOCAL POOL PUMP MOTOR REPAIR GUY WITH FREE TESTING.. WARNING THESE CAPACITORS HOLD HIGH VOLTAGE AND WILL NEED TO BE SHORTED ! USE A DRY RAG AND COVER CAPACITOR THEN SHORT WITH SCREWDRIVER

IT HELPS IF YOU HAVE THE RIGHT PICTURE OF YOUR MOTOR OR MORE INFO.. BUT GOING FROM THE PICTURE THERE IS A CAP UNDER THE LITTLE BUMP ON TOP OF THE MOTOR, IT'S CALLED A RUN CAP AND WILL STOP THE MOTOR FROM STARTING.. SEARCH YOUR LOCAL AREA MOTOR FREE POOL PUMP MOTOR TESTING.
ITS TIME FOR A NEW SHAFT SEAL, SO YA CAN KILL 2 BIRDS WITH ONE STONE ... HAVE THE SHOP REPLACE THE SHAFT SEAL! AND ASK THEM HOW YOU CAN TAKE BETTER CARE OF YOUR PUMP? ....... REMEMBER TO ALWAYS PRIME THE PUMP AFTER A REPAIR !... THUMBS UP PLEASE ...JAY

WD40 IS A WATER DISPERSANT AND WILL CAUSE MORE DAMAGE THAN GOOD ,IT WASHES AWAY OIL AND GREASE.. YOU MUST HAVE THE START SWITCH SET ,IT SHOULD BE CLOSED FOR START AND OPEN WHEN RUNNING.. NEW BEARINGS ARE THE ONLY GOOD FIX . YOU CAN TAKE THE BEARING IN YOUR HAND AT A SLIGHT ANGLE AND SPIN THE ROTOR, YOU CAN FEEL ANY BEARING DAMAGE THREW YOUR HAND I'M YOUR LOCAL POOL PUMP REPAIR GUY IN LONGWOOD FLORIDA. WHERE THE POOL IS ALWAYS OPEN

check for a re-set button somewhere on the motor housing.

It is a capacitor problem. Motors use capacitors to start. Your 2 speed motor should have 2 capacitors (or 1 capacitor with more than 2 connections). Changing this capacitor should solve your problem.