According to the Tilden chart for the Schneider 270f, the intake valve should open 27 degrees before Top Dead Center on the exhaust stroke, and the exhaust valve should close 23 degrees after TDC.
https://www.tildentechnologies.com/C...rformance.html
If you have a TDC mark and a protractor you should be able to check the cam/valve timing by observing valve action through the spark plug hole (a dial indicator would be helpful to pinpoint the start or stop of valve motion). There are 44 teeth on the cam gear and 22 on the crank gear. One tooth off = 360/22 = 16.36 degrees of crank rotation.
One tooth early would have intake opening 43 deg BTDC and exhaust closing 6 degrees after TDC. One tooth late would have intake opening at 11 degrees BTDC and exhaust closing 39 degrees ATDC. Either error should be pretty obvious by watching the valves and the TDC marker.