Performance Gearbox


XS650 Junkie
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Devon, United Kingdom
I’m rapidly approaching the process of rebuilding and my engine I’m wanting to show a little/lot of love to the gearbox. I’ve done a lot of research & sourced 3rd & 5th from an XS750 for their stronger dogs and I’d also like to do the work @Ratranger did, namely undercutting of 1st gear dogs.

So before I have all parts super finished does have any more information on this work?

Also I have a spare transmission from a XS1 and I believe that the parts aren’t interchangeable with the later transmission?

You are correct transmissions are not gear for gear interchangable. Whole transmissions may be interchangable.I am not sure others will know for sure.
The tell is the notches in the gear teeth on later gears, earlier gears do not have them. I have seen a dealer advisory notice about this somewhere on this site.
So far as what you have done to improve the gearbox is good the only thing I would add is careful shimming or ensure the shims are all installed in the correct places.
Also it is possible by changing the shims on first gear to get the dogs to engage a bit more, however with back cutting as the load goes on the dogs enmesh more so this is probably superfluous.
Super finishing will be a nice touch.
Just had a further thought, later after you have finished the core you could get a set of high ratio primary gears. They are not hard to fit and come with instructions.
The clutch basket and cover need to be slightly modified nothing dramatic. I am told the higher ratio primary gears have the advantage of reducing the stress on the gearbox as well as overall higher gearing.
Ivan Hoey in Australia is one supplier, possibly Smed speed as well.
I don't think you will really have problems with the gear box as they are pretty robust but they are all getting on a bit now and we just cant help ourselves trying to coax more giddy ups out of the old dears.
Hi @Signal

I originally sourced the XS1 gearbox as I read that 1st & 2nd gear were a little closer together than on later transmissions and I thought that would be cool to incorporate.

It’s also worth noting that according to the information on Smedspeed’s site Yamaha changed the profile of the teeth of the gears on later models.

Not to worry, it’s another parcel to add to the collect on the shelf (I’ve become a bit of a hoarder at this point).

I actually do have a set of Ivan’s primaries along with a billet clutch basket to go into the engine.

77 Yamaha changed the gearbox shaft profile.