Small Engines (Lawn Mowers, etc.): 25 hp itec smokes, spring tuneup, oil dipstick

Question
I just did my spring tuneup on my craftsman tractor that has a 25 hp Intec ohv.  I noticed that at start up and when running under a load I get white puffs (maybe blue) of smoke.  I ask the guy down at the mom and pop lawn mower repair shop and he told me the ohv need to be adjusted every year.  Is this true?  This is the third engine on this tractor , all replaced by sears.  Any help would be greatly appreciated.

Answer
WOW!  3 engines?  I would start by checking the valves.  A leakdown test will provide a good indication of the internal engine parts.
Do you have a oil dipstick on the engine?  If so, does it have an o-ring seal at the top and bottom of the tube?  The o-ring may be on the dipstick.
What oil brand and weight are you using?
Let me know.
Eric