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Small Engines (Lawn Mowers, etc.)/B&S motor on Craftsman Lawn Tractor


I Have a sears rider mower with the Briggs 15.5 hp OHV IC platinum engine, model 28N707 type 0173-01. I had replaced the flywheel gear ring, as the original plastic one had some teeth sheared off.  After reassembly the engine started up ok, then would not restart.  I found that it had sheared off the flywheel key. The engine is backfiring as well.  I adjusted the mag air gap as well as the lifter gaps.  It starts up and quickly shears off another key.

I'd start by lapping the flywheel taper to the crankshaft taper.  This only takes a minute or two and you only need a little lapping compound.

Second, were the any washers under the flywheel nut/bolt?  Most of the time there is a washer and if you forget to install it the key will shear almost every time.

Let me know if lapping the parts helps.


Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


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.


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.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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