I have a 5 year old Troy Bilt Pony 42" cut with the 15.5 Briggs and Stratton motor. I was mowing today and the motor made a clunk sound, quit, and now won't start. When the crank is spinning after I let off the key, there is a clicking noise as it spins down. Could it be new mower time or does anyone think it will be a inexpensive fix?