I fill the crankcase to the full mark on my 17 hp Briggs motor, and for some reason it disappears after a couple of mowing. I can not see and leaks etc

Where is my oil going if I can find no leaks any where

You could have bad rings and are burning the oil. Any smoke from the exhaust, have you doen a compression check yet? Do a compression check, record the number, add a table spoon of 30w through the spark plug opening and test aggain. How different are the readings?

You could have bad rings and are buring the oil. Any smoke from the exhaust, have you doen a compression check yet? Do a compression check, record the number, add a table spoon of 30w through the spark plug opening and test aggain. How different are the readings?

It does not smoke at all the oil just disapears some place
hardrock

How much oil is it using ?

Did you do the compression test yet?