Honda BF50 (5HP) BF5A Outboard Motors Shop Manual., Page 20Get this manual
ONDA 4VALVE CLEARANCE
NOTE: Check and adjust the valve clearance when the engine coldA 1) Remove the cylinder head cover and align the "T" mark on the flywheel with the "AT" mark on the ignition coilMake sure that the piston is TDC of the compression stroke2) Measure the clearance between the valve and the rocker arm by inserting thickness gauge
Valve clearance
1 0.1 1-0.19 mm (0.004-0.007 in)
1 LOCK I[2] ROCKER1ARM NUT 131THICKNESS