BRP Johnson 4HP Service Manual page 82

POWERHEAD
DISASSEMBLY
4. Remove the gasket, the dowel pins and the push rods
from the cylinder block.
5. Remove the valve adjusting lock nuts 1, then remove
the pivot nuts 2 and the rocker arms 3.
6. Using the special tools, remove the valve cotters 4 while
compressing the valve spring.
 Valve lifter
Attachment
Tweezers
7. Remove the valve spring retainers 5, the valve springs
6, and the valves 7 / 8.
8. Remove the rocker arm pivot bolts 9 and the rod guide
plate 0.
 Deep socket wrench
6-8