I was cutting pastures for 1+ hours when the tractor stopped running with a puff of white smoke coming out the side of the engine. I tried to restart but starter did'nt turn over yet dash lights were on as normal. I let it cool down for an hour then checked the oil, antifreeze level, radiator blockage and battery, all were normal and it started right up. Started cutting again for 10 minutes same thing happened. I looked at electrical connections at starter, distributor and battery, no loose / corroded ones found. Any suggestion where to look next?