BS90 Tranny

[Jjeritza]

Hello all, I just purchased a 90 trail last month.  It runs but could use some carb work but the tranny has me a bit puzzled.

The few times I have road it since snow has left I have had issue where I believe it is on neutral and go one click down and in what seems to be fourth gear.

I have then clicked back up a couple of times and ended up it seemed in first.

Is a rotary transmission supposed to do this or is there some stop that only should let me go down to 4th and up to neutral.  The shift fork seems a little worn so not sure if this, some stop missing or something else.

Any help would be appreciated!

thanks-john

[rwgibbon]

John,

Check the manual, page 32 for the details of the transmission.
(you can download a copy from this site, look under manuals 90 Technical
Handbook)

Hope this helps.

Randy

[disc_valve]

Hi,

sounds like you've just got a standard rotary transmission. It was designed so that rider could b e lazy at stop lines - pull to a halt in 4th gear, then change "up" once more and you're back in neutral. The danger is that it is possible to go from 4th to 1st while moving and the bike doesn't like being put into 4th gear at 40 mph.

You can use the rotary box just like a normal 4-speeder return change, but ... if you are at speed, think you are in "3rd", change up and miss the gear, THINK AT LEAST TWICE before you prod the gear pedal again.  You may already have been in top, not 3rd, and one more prod will take you into 1st. In those situations I will always change back down to the lower gear and re-assess things.

The 175/200 had the rotary option selectable by moving a lever on the side of the transmission case you could either have a 4-speed rotary or a 5-speed return change pattern. Some of the later model 90s and all the 100s had a return change pattern instead of a rotary shift, but that requires a different shift drum and drum stoppers.

Hope the answers your question,

Graham

[paul]

I never owned one, but I thought the 100cc Bridgestones had the rotary gear change pattern also.

[disc_valve]

Hi, Paul,

You may be right - all I can say is that my TMX has a return change, and so did the Oil Injecton 90 Deluxe I owned years ago. My TMX engine was built up from a seized BS100 Sport engine and a box full of surplus 90 parts, but I'm sure I used the selection mechanism from the 100Sport. I assumed that the return change came in as standard with the "Jet-Lube" system, but it is possible that the later bikes also came with either  type of gearbox.

Graham

[paul]

the August 1967, Cycle magazine test of the new BS 100 trail comments on its rotary shift pattern. The test is archived on this web site.