Small Engines (Lawn Mowers, etc.)/BROKEN FLYWHEEL

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Question
QUESTION: HELLO MR. JONES, I HAVE BOUGHT A CRAFTSMAN RIDING MOWER MODEL 917.288517 SERIAL NO. 0918130028551. IT HAS A BRIGGS AND STRATTON 21HP. PLATNIUM ENGINE XRD 540CC. THE ENGINE WAS LOCKED, I REMOVED THE FLYWHEEL, AND FOUND THAT HALF OF THE MAGNETS CAME LOOSE AND WIPED OUT THE ALTERNATOR. THE FLYWHEEL PART NUMBER IS 591759. MY QUESTION IS THE PRICE OF A NEW FLYWHEEL IS $142.00. IS IT NORMAL FOR THIS TO HAPPEN, AND IS THIS THE ONLY FLYWHEEL THEY MAKE FOR THIS ENGINE? THE ENGINE MODEL NUMBER IS 331977-0010-G1 CODE 13073020. I APPRECIATE ANY INFORMATION FROM YOU, BEFORE I PURCHASE ANOTHER FLYWHEEL, THANK YOU, AND HAVE A GREAT DAY! FRED

ANSWER: Yes, that is the only flywheel they make for that engine.

I have seen some of the magnets come off like you described...and yes they ruin the alternator stator.

Since you do not have an electric PTO clutch you do not need much of a charging system.  You could remove the rest of the magnets and use the flywheel as is long as it is not cracked...don't want the flywheel to grenade at 3300 RPM...you could get seriously hurt.

The only thing is the battery will NOT charge so you will need to charge it regularly...I would recommend a Battery Tender.

Flywheels and stators can be expensive.  Have you checked Ebay for used parts?  Most Briggs stators are interchangeable...they just produce different amounts of power in the small stators.  I'd recommend getting the same one currently on your engine...just easier to remove and replace.

I don't know exactly why the magnets come loose once in a while...bad glue, excessive heat?

Let me know if this helps.

Eric



---------- FOLLOW-UP ----------

QUESTION: IF I BOUGHT A NEW ALTERNATOR AND USED THE SAME FLYWHEEL WITH HALF OF THE MAGNETS WOULD THAT WORK?

Answer
It should work but the charging will be a little slower.

The charging system produces AC as the magnets rotate around the stator coils.  There is a diode in the stator harness that converts the AC to DC for charging the battery.

If you have a voltmeter I would check the battery DC voltage with the mower off.  Start the engine and run at full speed and check the voltage again.  As long as it is above 12 volts DC and less than 14.7 volts DC the battery will charge.

Do you thing the other magnets will come out and ruin the new stator?

If you notice the engine vibrating more than usual then the flywheel is too far out of balance due to the uneven weight distribution of the magnets and you could cause some damage on the upper main bushing of the engine.  The magnets are pretty light in general so I doubt you will notice any issues or cause any problems.

Eric

Small Engines (Lawn Mowers, etc.)

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Eric A. Jones

Expertise

Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.

Experience

Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

Education/Credentials
MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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