Since I've been riding with the SS50 motorcycle it has had an original unmodified 5speed engine. Now only the ports and valves have been lightly tuned, but wat has been buggin me from the start; the short first gear compared to the closeness of the rest of the gears.
My other engines have 4speed gearboxes, that have a problem with a big step between third and fourth, but that is not as annoying as the 5speed first gear.
Also this is dangerous, as the 5speed gearboxes are known to break when shifting from second to first while riding, or they break when not properly kickstarted, as the gears are to narrow and the kick-gear only engages for a few millimeters.
(Three out of four of my 5speed gearboxes had a broken first gear)
To avoid breaking and to get a closer gearbox, I decided that the "oldschool-tuning-engine" although newly built and never run, was going to be opened up to change out the first gear for a modified first from a 4speed gearbox.
Thanx to my dad for the modifications of the shaft and sprocket.
Top: modified 4speed first gear (13:35)
bottom: original, broken, 5speed first gear (12:36)
And some other tricks that have been applied to this engine:
Old copperplated rockers, lightened.
Thin homemade cylinderbase gasket.
2-plate clutch to prevent slipping, please forgive me for it is from a chinese engine.
But to make up for the chinese clutch, an S65 clutchcover with homemade finned adjustment cover. Note that there is no indentation under the adjustment cover as in the later types, this means 0,73L of oil instead of 0,7L.
On the front is the oil line for the carb-heating that is blocked of now, I want to use this for an oil-cooler in the future. And mounted onto the filler opening, a nice breather unit like the one on my RSC90.
And a lightened cranckshaft, turned on the lathe to remove weight, but only where it could be removed over the full 360 degrees so I didn't have to balance the cranck again. And onto that a new high compression piston, not the old one from the SS50 5speed models, but from some new dax, it has the same compression ratio, but it weighs 20% less.