Engine Should I be looking for a repair shop? White smoke from muffler upon startup.

[Dogband]

Cub Cadet 1042 mower with Kohler Courage 19 engine, 350 total hours over 7 seasons. The last few mowing sessions would yield white smoke coming from the muffler after just a few minutes of running the mower. This occurs for 2-4 minutes, it is not just a very passing brief puff of smoke. After 4 or so minutes it stops smoking. The engine seems to sound and run as well as it ever did. In my lack of mechanical knowledge, it seems as if oil has somehow been forced into the exhaust, and it takes a few minutes to burn it off. I have cleaned and oiled the foam air filter regularly, but have been guilty of not changing the big paper filter with due diligence. Oil and filter has been changed every season, as well as fuel filter. Spark plug changed once. I cannot tell that my oil level is being depleted. Do I have something as simple as needing to replace the big paper air filter, or do I need to be finding a repair shop now before the season starts? I would probably just take it into a repair shop for a pre-season checkup, but in my rural area, there are very few, if any, repair shops that get good reviews. Thank you for consideration of my issue.

 

[bertsmobile1]

Run the engine for 10 minutes then turn it off & pull the dipstick out.
If you are getting smoke from the dip stick hole the head gasket is gone.
This is an easy fix it yourself job.

Pull the engine breather pipe away from the carby and start the engine.
If it blows a lot of oil out of the breather with considerable force then the rings or gasket is gone.

Hold your finger over the end of the breather tube, it should blow, wait, blow wait, blow wait.
If it blows-sucks-blows-sucks-blows-sucks then the reed valve in the breather is gone.
This is an easy fix.

Take the rocker housing off and check the heights of the valves when the piston is just past top dead center on the compression stroke.
If one looks higher than the other then good chance the head has overheated and the valve guide has shifted in the head ( unusual for Kohlers )

Finally remove the carb and try to inspect the inlet valve stem.
You will most likely need a little mirror to do this .
If you see tracks of oil or burned oil deposits on the stem then the valve stem oil seal is gone.
This is an easy replacement.

White smoke is generally partially burned oil, vapourising in the muffler.
Greyish white smoke is oil burning in the cylinder and is usually accompanied by oil fouling on the spark plug