One of my changes from the last build was how I created the head and valve and valve guides.
The second try for making valves went much better. Practice makes better. I started with standard 3/8" round stock.
The valve guides are 3/8" brass that are held with locktite. My change in process was in the valve lapping. The last time I used a flexible tube attached to the valve with a plastic tube. Use polishing compound and spin the valve in the guide with a drill. I had a tough time getting a seal.
Mostly because of my poor technique making the valves.
This time I put the valve guides in the 3C collet and valves in a drill chuck in the tail stock. This way everything is concentric. I did three steps, valve grinding compound - rubbing compound - polishing compound. It was probably overkill but it worked.
One unexpected behavior was the intake valve spring. I was told that all the spring has to do is keep the valve from falling out. Maybe for smaller displacements. With the 32mm piston there is still enough vacuum with exhaust valve held by the governor to pull the intake valve to full open. On the compression stroke with the exhaust valve held open the intake is slow to close and it blows back through the carburetor. I needed to use a much stouter spring.
The second try for making valves went much better. Practice makes better. I started with standard 3/8" round stock.
The valve guides are 3/8" brass that are held with locktite. My change in process was in the valve lapping. The last time I used a flexible tube attached to the valve with a plastic tube. Use polishing compound and spin the valve in the guide with a drill. I had a tough time getting a seal.
Mostly because of my poor technique making the valves.
This time I put the valve guides in the 3C collet and valves in a drill chuck in the tail stock. This way everything is concentric. I did three steps, valve grinding compound - rubbing compound - polishing compound. It was probably overkill but it worked.
One unexpected behavior was the intake valve spring. I was told that all the spring has to do is keep the valve from falling out. Maybe for smaller displacements. With the 32mm piston there is still enough vacuum with exhaust valve held by the governor to pull the intake valve to full open. On the compression stroke with the exhaust valve held open the intake is slow to close and it blows back through the carburetor. I needed to use a much stouter spring.