by Mutt » Tue Sep 12, 2023 10:35 am
You don't give up top end, just change the rear wheel sprocket to suit your needs. Harley didn't do much to improve the little bikes as the bike bikes were their top sellers. A 3hp 125cc having a 43 tooth rear sprocket is insane. It would be find if ya had a 8 speed gear box. It was fine for getting from point A to point B in the 50's, bt was not performance oriented. H-D did come up with a 47t wheel sprocket around 1951 for the 125. This was an improvement over the 43t. Then in 53, they dropped one tooth on the main drive gear (27t), which was another improvement, along with a 49t wheel sprocket. Then in 1954, they dropped another tooth from the main drive gear (26t) which was yet another improvement. BSA was making different gear sets during the 50's for the Bantams. In 1959, Harley offered yet another (accessory)main drive gear with only 25t, which was also an improvement,along with a one tooth drop in the second gear set (accessory). In 1962, the final improvement was made, when they offered a 24t main drive gear (accessory).
The low gear was even lower on the 48-51 models. You may have noticed that you run out of gear within 20 feet from letting the clutch out on these early models, and only about 30 feet for the 52 and later models. Its cost the same amount of money/labor to make the gears and shafts, regardless of the tooth count. In my opinion and from 34 years of building these motors and riding them, the best transmission would have a 17/30 first, a 22/25 second and the 24/21 third. Various wheel sprockets for speed or top end.