General Category > Bike Builds, Rebuilds And Restorations Only
Sessantacinque GT rehab (V65 GT), frame crabbing, gear box, transmission
Pescatore:
Looking around the box, I found these two interesting stamps. I guess the box was cast in 1983?
I cannot make out what the other stamp says.
The next step is to remove the vent because it has a detente pin that slides into slots on the fork drum to stop it at the right position (see top of drum below).
I added a banjo to the vent to route any overflow into a bottle next to the battery. You don't have to remove the neutral switch.
Next, undo all the allen screws at the back of the gear box. The housing comes off with a few taps. This is another view of the guts:
When I first opened the box, the gear selector was in a position similar to below:
After a few hours of shifting gears and observing how it works, I realized that the shifter was returning to a bad position.
Except for 1st, neutral and 5th, both teeth are supposed to touch a pin of the drum. For neutral, the first drum pin should be in between the teeth.
In 1st, the inner tooth should be touching the first pin and in 5th the outer tooth should be touching the last pin.
This is neutral position, also noted by the two round cutouts on the bottom plate of the drum lined up with the shifter teeth:
The cutouts (easier seen on next picture) should allow you to remove the drum without removing the shifter.
This is second gear. Note how the teeth are touching the pins. I could hear a click when both teeth snap onto the pins of the drum, ready to move to the next gear.
BTW: I had to keep spinning the shafts to get the forks to move.
After a few more hours and just about giving up, I tried different positions of the eccentric screw, one flat at a time. I marked the nut where I started.
On the fourth try, I started getting repeatable shifting and the snappy sound of the teeth grabbing the next pin of the drum.
Did I fix it? I don't know for sure. The real test will be when I run it at speed.
Pescatore:
After much thinking and recurring bad dreams, I decided to check if shifting works while the gears spin.
I attached a drill to the lay shaft and spun it slowly.
Only three gears were engaging, WT...???
I turned the eccentric screw again and got to a position where all the gears clicked in. The downshifting is especially smooth and I can even find neutral.
I was turning the screw by one nut face at a a time, like I read online.
That was too much. It needed to be in between. Seems too finicky, but it works.
Time to reassemble everything. If it doesn't shift once installed and warmed up, hopefully the screw will be the answer.
I still have to figure out how to properly torque the big nuts.
Canuck750:
Great work! impressed with your dedication to sorting it out. I have never seen the model you are working on, its an attractive bike.
I find transmissions, especialy getting the shift to smoothly function up and down a real challenge. I have had more than one transmission out and stripped several times before I understood it and sorted it.
Pescatore:
Thank you, Canuck! :bow:
Muzz:
--- Quote from: Pescatore on May 07, 2022, 12:58:25 PM ---
--- End quote ---
Never thought of doing it like that. :embarrassed:
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