Selector box adjustment??

[Bevel bob]

I have been having the odd missed gear 1st to 2nd and reading that the external adjuster (ecentric) has to be set in the mid position i foolishly fiddled with it prior to a club run. The journey there was without benefit of 4th and 5th , another fiddle and the next 50 miles often unable to change down to 1st or 2nd, I did not think this was a senstive item, where did i go wrong??.

[Jordan]

It's a sensitive item. It's not difficult to fix, assuming all that's needed is adjustment.
Ride your bike with a 10mm spanner and small blade screwdriver with you. Loosen the locknut and turn the adjuster slot a very small amount in either direction, and retighten nut. Ride and note if gear change is better or worse. If better, repeat until gear change is nice. If worse, turn slot in the other direction, etc.

Jordan

[Bevel bob]

Hi Jordan, I was hopeing for a technical explanation!! , I always carry a selection of tools, I am also a bit concerned that the ecentric cam is not now in the right position to bear on the fork , i think the case is threaded and the ecentric may be too far in , i suspect that it should be turned anti clockwise till it meets the back of the box, then adjusted?.

[LaceyDucati]

Bob

The eccentric is just an off set circle to the screw, the casing is not threaded so the screw just goes round & round. Effectively the off set circle sits in the slot of the spring plate & from it's central position only has effective movement of 90 degrees maximum. If you turn it more than this, the circle will disengage from the slot through the next 180 degrees & just give you movement in the mechanism and make things worse. Assuming you have lost the central position, the simplist way to reposition this is to remove the back & have a look. A tip is to leave the pedal attached to the selector box as this will prevent the mechanism from potentially popping apart when you are just having a look. In this position you will clearly see what the eccentric is doing and be able to position it back between the slot. All the eccentric does is move the claws in relation to the pins on the selector plate. In a perfect world the claw should be positioned with an equal gap to each pin. Unfortunately manufacturing errors means that by the time you move the plate through its various positions you will find the pins move about a bit relative to the claw. Best thing is to position the claw somewhere centrally then pop the back on and mark a position on the cover with a pencil relative to the slot. With the selector box off the bike and mounted firmly if possible, change through the gearbox up and down slowly. When you move the pedal to change gear you will hear a click and when you release the lever, you will hear a second click. If you don't hear a second click (not counting when you get to 1st or 5th) the mechanism is hanging up. More than likely you will find that the mechanism is hanging up either on the up changes or the down changes. By experimenting with a small adjustment of the screw you will find that you will probably get all perfect changes in one direction and it will be hanging up in the other direction. The trick of course is to get it so that it works both ways.

My way of adjustment is to get it to hang up in one direction then turn the screw until I hear a second click, then make a pencil mark in this position.

Then I turn the screw until it hangs up in the other direction and move the screw until I hear a second click and make another mark.

I then move the screw to a mid position between these two marks and that will be as good as it gets.

If of course its still hanging up in one or the other direction to any extent then you probably have too much slack in the mechanism and you will need to strip the box and rectify this. In practice slight hanging up of the mechanism on the bench will probably not come to anything on the road as general vibration and inertia will return it to a central position.
Hope this points you in the right direction,
Best Wishes, Nigel

[Bevel bob]

I just Knew it had to be complicated!, the simple things always are. Thanks all.

[3564cam]

Hi Bob,
I had exaclty the same trouble with my 125 Sport till I rebuilt it with new parts from Nigel.It now works fine and makes all the right clicks

[Bevel bob]

Hi 3564cam, I had a very bad trip 50 years ago with a Rudge gearbox, and its left me with an aversion that still haunt's me.Perhaps with the help of forum friends i will finally put it behind me. I'm going in ---God help me!.

[LaceyDucati]

Good Luck Bob, give me a call if you get stuck. Failing that if it all proves to be too traumatic, I do offer a rebuild service
Nigel

[Bevel bob]

I think i'm on top of it, the Rudge Ulster Box was a nightmare,full of cascading needle rollers and infinate adjustments, and i was only 16 .

[Jordan]

You don't need to dismantle anything, if you follow my suggestion for adjusting the selector box. No harm can be done. Of course we all keep a full complement of tools with our bikes but you want them in your pocket for quick access, when you're starting and stopping during the adjustment process.

Jordan