Hi There I have received a letter from a reader about the free Zephyr plan. He says that the con rod needs shortening and the depth of cylinder head clearance needs reducing to match. I will post exact details soon but don't make thes two parts yet. regards David
Hi There The errors have been on the drawing since 1947. We can hardly blame new technology. Errors are (as reported) the piston will not fully uncover the exhaust and transfer ports in the cylinder liner. To correct the error, the con rod should be 1.320in. centers, not 1.375 in. as drawn.
To avoid excessive clearance in the cylinder head after shortening the con rod, the combustion chamber should be reduced to 0.125in. depth and the spark plug seat should be spot faced 1/16in. deeper to suit the plug.
The spring steel blade is 1/32in. but is to stiff so 0.018 spring steel should be used. regards David
The Zephyr plan is almost exactly twice scale. On the conrod view the length is shown as 1 3/8ths ins. But on the sectional side elevation view the conrod only measures 2 3/8ths ins therefore at half this the rod should be l 3/16ths, not 1.320 Since the rod is in situ vertically in the sectional view, this must be true to the double length. ETW made exactly the same error on the Atom Minor 111 - I know - I had to scrap the conrod and make a new one. Tomol.