Words and pictures: Alan Dowds
THANK the stars you weren't riding bikes in the 1940s (or maybe you were…) Back then, materials were so basic, that things like engine intake and exhaust valves wore out fairly quickly, and 'grinding valves' was a regular maintenance task.
For a four-stroke engine to work well, it’s vital that the poppet valves in the combustion chamber make a solid, gas-tight seal. That's achieved by grinding each valve into its matching seat, so they fit perfectly, with no gaps for gas to leak through.
Nowadays, it's not a regular task on modern engines, but whenever you have a cylinder head apart, you should check the valves and regrind them if the sealing faces aren't completely smooth and clean.
Over the next five pages we’ll show you how.
1. Check the seats
You want to examine both the valves, and the valve seats in the cylinder head. Any serious damage will need a proper professional fix – re-cutting or replacing the seats in the head, or replacing the valves. These Kawasaki valves are just a bit grubby, with a build-up of carbon and some mild pitting from oxidisation. The seats are fine, so we're okay with a moderate regrind.