Filing a keyway in hard steel is not easy- I found a carbide file was the only way.

 

 

 

 

 

Big lump on the piston tends to mask the spark plug...in fact I am having to use on the flat surface discharge types because things are so tight the piston suffers from spark erosion

 

Flywheel flank is relieved at the main bearings

 

just bought a 50ml graduated cylinder to accurately measure the combustion chamber