Every time I start it blue smoke billows out, and then clears up. It seems to sound knocky and rattly then that seems to quiet down too. I suspect that the rings are letting oil in at cold startup then the piston and rings expand when it warms up. This is a WAG, but seems to be what its doing.

Valve seals. A compression check with and without oil in cumbustion chamber would confirm.

What's the model #
Make sure its not over full on oil

I have checked the oil level several time to confirm this isn't the issue (right or wrong I even ran it low on oil at low mark on stick to verify.). I hear a lot of engine knocking noise that seems to get quieter( or I get used to it).

Checking compression use gauge and crank engine with the key? What should I expect?
I do not have the model number at this moment. It's on an older 70-80's vintage simplicity 4212 tractor.
Thanks for the help.

I am not afraid to dive right in and tear it down but would like to start with the basics. Keep It Simple Stupid does apply to me.
Thanks all.

Hi,
The Briggs recommended way to test is flywheel bounceback. With the blower housing removed, rotate the flywheel backwards to the compression stroke, reverse about about half a revolution and spin toward compression. A healthy bounce is about 90 degrees.
Peace,
Clarke