I'd been having problems with the motor stopping in tight downhill turns with the clutch pulled in on my 52 years old model 49
so started with checking how much clutch pushrod travel I was getting. The mechanism is a multi-start worm or "bendix" that was phased out on
in about 1969 but was continued to be used by other manufacturers (Suzuki, Yamaha etc) for a while longer until the Japanese caught up with
design advances (that bit was especially for Graham Weiss).
There was a bit of play in the bendix on the bike so I thought I'd take it apart and have a good look at it.
Here's what a bendix looks like. The one in the photo is actually a less-worn bendix than the one that came out and it was nice and clean so got used for the photo. .
The clutch cable goes on an arm that twists the male part of the bendix and it sits in the engine cover like this.
The male part of the bendix has an adjustment screw through the middle to set the free-play for the pushrod and the end of the screw is what pushes against the clutch pushrod. The clutch pushrod sticks out the end of the gearbox shaft that carries the front sprocket and has the clutch on the other end.
The clutch pushrod has a rounded end to create point contact with the normally-flat end of the screw, to minimise friction while the clutch is pulled in.
This bike though has seen enough hours with the clutch pulled in that the end of the adjusting screw has worn, eventually becoming a hollow depression that perfectly fits onto the dome on the end of the pushrod. I'm not sure you can see in the photos but the end of the screw has turned blue from heat and has belled out. I suspect that the friction there might be what has been causing the motor to slow down and stop when the clutch is pulled in and the bike comes to rest. So I'm going to make the end of the screw flat again and see if the problem is still there.