'48 G80 Rigid Speedo Drive

[Iron Head]

After a few 'laps' around the garden on this rebuild with no speedometer cable yet mounted I noticed that the rear speedo drive has rotated. I read the horror stories of later models rotating and wrapping up cables if the drive nut is not correctly tightened.

I have rebuilt the rear hub and hopefully got everything adjusted and assembled as per the manual but is this rotation to be expected and is it just the fixing of the cable to the frame that prevents this rotation from happening or is something awry?

Advice gratefully received as always.

Iron Head

[Rob Harknett]

Did you lock up the speedo drive nut after the wheel was in the bike all tightened up. You can only tighten and undo this nut when the wheel is fitted and all tightened up. I am sure cotton reel hubs are the same as full width as far as that is concerned. Some one will correct me if I am wrong.

[Merlin]

The great late Alan Jacob always said the last thing you do is tighten the speedo drive nut.

[clive]

No speedo drive nut on single sided reel hub. The only thing that keeps them in place is the spacers and the fact that the nut on the far left hand end of the spindle is done up tight (looking from behind the bike). It should not rotate once the spindle is done up. My inclination is to ask did you do up both sides of the rear spindle? The spindle itself has large lump on it which goes on the right hand side of the wheel looking from the back of the bike. One side of the lump butts up against the frame, the other side butts against the speedo drivebox. This must be the earlier type with a hole in it only slightly larger than the spindle diameter. The two pegs in the speedo drivebox engage with two slots in the cottonreel hub. Behind that is a spacer that butts up to the inside of the drivebox on one side and the end of the hollow spindle for the bearings at the other. When you bolt the spindle up the right hand side just locks the frame against the lump. You have to also lock up the left hand side which should then stop the speedo drive box rotating.

The cottonreel hub does not suffer from the horror story if installed properly. At worst if the drivebox locks up due to wear it chews the slots in the hub up as the pegs in the drivebox get destroyed. You can then just cut some new slots or make do with the damaged slots when fitting the new drivebox (been there got the t-shirt).

When I bought my first AMC machine, a 1949 rigid G80, I rode it about 20 miles home across London. It was only when I was looking it over that I realised that only the right hand side of the spindle was tight. The left hand side , if tightened up simply locked up the rear wheel. the right spacers were in the wrong order. Reassuring that the PO allowed me to drive it away knowing the rear wheel was only being held on by the nut on one side and the chain and brake plate on the other.

[Iron Head]

Thanks for some great advice and pointers there Clive. I have to remove the rear wheel anyway to do some work on the alloy mudguard to attach the number plate/light. Although I followed what was there when I disassembled, cleaned and repacked the hub I'm going to do another careful strip-down of the hub and re-trace my steps, may well be something wrong from when the last owner 'tinkered' (some time in the sixties) and perhaps replicated your London ride scenario!

Iron Head

[clive]

That was 37 plus years ago but if I remember correct it was either the order or the way round of one of the spacers inside the brakeplate side of the hub. Instead of squeezing onto the centre hollow spindle it was pushing on the outer bearing race. The same symptom could be caused if the spacer behind the speedo drivebox on the other side was not long enough. Instead of holding it away from the wheel it would then be crushed into it locking the wheel. Rather than take your hub apart lock up both sides of the spindle and see if a. the wheel turns freely with the brake shoes centred, b. the speedo drivebox is rigidly secured so there is no movement however hard you pull at it. If it passes those tests its probably ok.

[Iron Head]

Well Clive you were right first time. Checked today and I hadn't tightened the sprocket side nut properly. Perhaps more haste less speed next time from me putting things back together!

What I am pleased about though is that I now fully understand how the G80 rigid rear hub works, the drawing in the manual takes some understanding. That machined-on-the-spindle right side spacer (facing from the rear) is simply a 'dead stop' that everything that needs to tightens up against (from the left) and, as you said, firmly mounting the speedo drive housing against the spacer in the process. Thanks again!

Iron Head