Engine's been working great for years, but just last week started puffing blue smoke intermittently. Approx 6-7 times during an hour long mowing session. No noise, just a puff of smoke apparently coming from the front and right side of the engine. What could it be? Will likely repair myself. Thanks.

Hi, Blue smoke is almost certainly oil being consumes in the combustion chamber. Usually this is caused by a pressure differential in the crankcase. The problem is that you must figure out its route to combustion. Possibilities are the breather putting it in the intake stream, sump gasket letting in air and forcing it through breather or past rings or head gasket doing the same as the sump gasket would. Infrequent oild changes will make it worse as old oil can do these things more easily.
As for whether you can fix it; this you must decide for yourself as you know your own skill level and supply of tools.
Peace,
Clarke