My gearbox was REALLY crusty. This is my first attempt at rebuilding a gearbox so all the USUAL DISCLAIMERS APPLY.
The first thing I did was remove the output flange nut and pull the output flange. This sounds easy. It was not. And I have the Cycleworks tool for this procedure and it was still very hard. Basically the tool screws into the 4 bolt holes on the flange for the driveshaft. It’s in two pieces- one is threaded to receive a pusher and the other is a kind of handle allowing you to prevent the flange from turning while you apply the torque.
The nut is 24mm. Using the tool and a breaker bar this came off fairly easily. The flange on the other hand was extremely stubborn. The idea is that the big pusher bolt with the ball tip is threaded into the tool and presses against the output shaft while the tool pulls the flange off. This takes A LOT of torque. I used a 5 foot pipe over the top of a breaker bar and secured the handle of the tool in my bench vise. I still couldn’t get it to break loose until I gave the pusher bolt a few sharp raps with a hammer. Then it finally broke loose.
Next I removed the kickstarter which involves removing the rusted nut and tapping the pin out backwards with a punch. Again, heat helped. The gear selector arm is the same.
After the kickstart the speedo drive gear which engages the gear on the output flange was removed. The sleeve can be pulled out and once the clamp bolt is removed. Then you can insert a screw driver and gently leaver the drive gear out.
Next, the lid of the case was removed. The seven rusty nuts and washers were removed. The lid has the bearings of the three shafts (input (blue), intermediate (red) and output(green)) mounted in it and like all bearings they are a tight press fit. So the lid has to be heated very hot around the area shown. When the lid is hot, there is a tool, or one can be made which uses the clutch lever pin and a pusher bolt onto the input shaft to pull the lid off. However, I was able to get it off very easily with a couple of gentle taps on the tab like area indicated by the red arrow and then gentle levering with a screw driver taking care not to mar the gasket surface. Take care to locate and preserve the shims on the output and intermediate shafts which sit between the bearings and the case. The bearing for the input shaft will have stayed in the lid, as it is kind of held in place by the kickstart idler sprocket.
At this stage things start getting interesting. I suggest taking A LOT of photographs and making a lot of notes. If you are planning on getting this thing back together….
Basically it helps to think of the gearbox in zones- there is the gear selector assembly on the left, the three shafts with the gear on the right and the two are joined by the shift forks, which are secured by two bolts to the case. The kickstart apparatus is attached to the lid.
I removed the two bolts securing the shift forks to the case to allow them to be free. I wanted to remove the selector assembly before the shafts, but I found it very difficult to access some of the circlips with the shafts in place so I went ahead and removed the shafts first. To do this I turned the box on its side and heated the area around the shafts to hopefully free up their bearings in the bottom of the box. When the case was VERY hot, I was able to start pulling and rocking the shafts (with gloves!) and get the shafts moving. I did need a little bit of gentle levering with a small crowbar to get them out but was very careful not to damage the gears or the case. I laid the shafts and selector rods aside in the same orientation.
With the shafts out of the case, the gear selector mechanism is easier to see and work on. There are numerous circlips which need to be removed and you should take great care to observe and record the order of the parts on the gear selector shaft. Finally all the rubber seals can be removed- there are 4; output shaft, input shaft, gear shift and kickstart.
When all the parts of the gearbox were disassembled I laid them carefully on some towels in exactly the position and order they would go back in. And did I mention I took a lot of photos?
Next the case will go off for vapour blasting, and then the box will be reassembled with new bearings, springs and seals. Also, the broken guide for the clutch cable will be getting repaired too. More to come!
