Gearing

[Emerica1975]

I’m building a st motor out of pieces from several engines. I’m going to use the engine for a bike to take to Davenport next year and hopefully race. Any way I ran into a little snag with my main drive gear 35051-47 with 28 teeth. Or I have the same gear with 27 teeth. The countershaft gear (35721-55) 19teeth or I have a countershaft gear with 20 teeth. The combination of main gear 28teeth and counter shaft gear 20 teeth won’t work but I could go main gear 28 teeth countershaft gear 19 Or main gear 27 teeth with counter shaft gear 20 teeth. I’m just not sure which combo would be better for this engine or if it even matters. I’m hoping someone will hav some advice. Thanks!!

[Mutt]

best to use the stock 54 and later 165/175 26t/19t combination. Unless you could find the unobtainium 24/21t extra close ratio -62R racing gears..............

[Emerica1975]

I have this for a 19t. But I’ll need to buy a 26t main drive gear. Do you have one you’d sell by chance

[Emerica1975]

If anyone has the close ratio racing gears they’d sell I’d be interested in those. As well.

[Mutt]

thats the wrong 19. It will have a -53B part #. I have some NOS ones

[Emerica1975]

Sounds good. Thanks for the info.

[Brent]

Years ago I was living in NJ and manning the HHC tent at Oley each year. Stan Waite would always wander by to say Hi and look over any parts that were being offered for sale. If there was trans gearing he'd always count the teeth and then set them back down. I'd watch him do this at other tables when I was out shopping. I once ended up buying a basket case bike from a guy in NJ being told it had been a racing bike but the motor had seized. It was a rusted wreck so I was able to buy it for next to nothing. It had a Pucket head and, when I tore the engine down, also had a stuffer plate. Remembering Stan I counted the transmission gear teeth. At the next Oley meet I waited for Stan to come by. When he did I handed him the gear set and told him "This is what you're looking for". He calmly counted the teeth and then asked me "how much?" I smiled and gave him a rather low-ball price as I was actually 'paid' by the look on his face (and knowing they'd cost me next to nothing and I had no use for them). He excused himself to 'go get some money'. Moral of this story: Never give up.

[Mutt]

here's some stuff from my personal stash -59R close ratio main drive gear set (25/20t)

59R set a.jpg (71.73 KiB) Viewed 40399 times

NOS 35720-59R close ratio 3rd gear (countershaft gear)

NOS 35720-59R.jpg (55.81 KiB) Viewed 40399 times

NOS super close ratio 1st gear and main shaft. Stock is 15t on shaft,32 countershaft gear. Count these teeth

[MrMarty51]

And so that is why it seems to be such a wide spread between second gear and third gear on My 57 125.
I wondered if there was a set that would bring the ratios closer together, but then, I realize I could do so at the expense of top enf MPH I suppose.

[Mutt]

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.