And now the modifications begin.
I was browsing eBay shortly after I bought the bike looking for interesting bits and one of the listings that caught my eye was for a close ratio gear box. The only problem with this was that I could find no information it. The part number 2AL-17400-1S-93 sure looks like a Yamaha number but it wasn't appearing on any part lists and even the seller couldn't furnish any more details. Even google was coming up blank. The only information I found was from the YSR50 forum which cast doubt on it.
However I'm a gambling man and negotiated with the seller, so didn't pay what was on the box as it had been sitting on their shelf for about 5 years or more. So I've either bought myself a brand new close ratio gearbox or a brand new gearbox.
Examination and comparison between the new and the old gear box shows that there are differences in the number of teeth on the cogs. If someone can explain what those differences are I'd be interested to know?
As well as the number of teeth there are some subtle differences in the cut of the gears and the shafts themselves. The bearings were new and supplied with kit but I used the ones that I sourced previously.
So with that I put them into the crank case. I say put, well, lets just say I want a word with the designer of the vertical split crank case and gear box designer as that was a pain. Getting the shafts in and lined up at the same time as the selectors and drum ensuring that they are all connecting where they should took much longer than it should. A couple of close attempts just resulted in the gears locking others just ended with selector forks slipping out of their slots. But perseverance eventually brought success.
And with that and some instant gasket the two halves were joined and the bolts tightened down. Getting the right hand side on was easy and the selection of gears was checked and all appeared to be there and running. But time will tell...