True 79cc iron sleeve build

[Greg58]

Here's where the bearings should be.

 

[Greg58]

I have one engine that I built with better crankshaft bearings, I removed the inner dust shield but left the outer behind the seals. It is the fastest 48cc I have, 76-77000 rpm with stock timing. I have it on a 24" tire bike, it will outrun my neighbors 48cc bike on a 26" tire bike and I outweigh him by 50-60 lbs. Look at the keyway cut location on all the magnets you have, some are cut different and improve timing. A good pipe with a longer head pipe helped me on low-end torque too.