My John Deere lx277 will not crank, just spins motor fast. Crank is working but the valves are not moving. I am guessing a broken cam gear shaft. Haven't rebuilt a small motor in about 30 years so I looked at replacements but very expensive. Should I do a limited rebuilt or do a complete one? I have had for about 25 years and it has been a great mower but I just bought a Toro Titan zero turn and love it but my wife is afraid to use it in our tree aplenty acreage. .Thanks for any suggestions.