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Ian Soady¹ said :-
Now for something slightly different. Again.
I was tinkering with the little C11 when I noticed that the back wheel would only rotate part of its circumference in both directions. I checked it wasn't in gear and removed the outer primary chaincase (I hate all those tiny screws!). Couldn't see anything wrong in there so started worrying about bent gearbox mainshaft etc so I stripped out the primary drive and removed the inner chaincase.
Then I saw it. Somehow a 2BA nut - no idea where from - had lodged itself on the lower rear chain run and was getting enmeshed with the gearbox sprocket / rear wheel sprocket so stopping wheel rotation. If I'd spent a little while longer pondering I may have seen it before all that work.....
Anyway, screwed it all back together but could I get the mainshaft retaining nut on against spring pressure? Could I buggery. I don't know why as I've done it before. Just getting weak I expect. After much thought I decided I could compress the spring in the cice and make a couple of retainers out of 16 gauge steel to keep it compressed. A crude version of spring compressors. I used a couple of cable ties to stop them making a premature bid for freedom.
The photos show the clips in place on the compressed spring with a couple of cable ties to stop them flying off. The next photo shows the spring in place with the clamps still on. I then screwed the retainer on by hand till it was nearly in contact then (very) carefully snipped the cable ties then wrapped the lot in a bit of rag and prised the clips off. No fingers damaged!
I have to say that was very successful. Maybe I should start making the clips and selling them at an exorbitant price!
Sorry about the quality of the photos - new phone.....
25/04/2026 12:40:57 UTC
Ian Soady¹ said :-
Spring in situ before taking the clips off:
25/04/2026 12:41:36 UTC
Upt'North ¹ said :-
That looks like one heck of a spring. Proper Brumingham spring arr kid.
25/04/2026 17:06:21 UTC
Ian Soady¹ said :-
Yes, it was pretty scary. I don't like springs, they sneak round and catch you when you're not looking.
26/04/2026 09:43:25 UTC
nab301 said :-
When you said spring I was looking at the photos saying what spring! until Upt commented and it all became clear, that is some spring...
Nigel
29/04/2026 13:06:31 UTC
Ian Soady¹ said :-
Just to explain what it is: there is no cush drive in the clutch or back wheel. The cush drive is the 4 lobed device just inboard of the spring. The theory is that power pulses (not very large as it's only a 250 single) are smoothed out as the cam faces move slightly under torque. A bit crude but very typical of prewar bikes.
30/04/2026 14:20:33 UTC
Ian Soady¹ said :-
.
30/04/2026 14:21:11 UTC
Ren - The Ed¹ said :-
I need a diagram or something Ian - I'm not seeing it in my head yet.
01/05/2026 07:56:48 UTC
Ian Soady¹ said :-
See below. The sprocket is free to rotate on the inner plain end of part 67-1097 (et al), which is is keyed to the engine mainshaft so turns with it. The sprocket has the 4 lobe cam shape to the left, and this engages with part 15-1555 which slides on splines on the exterior of 67-1097 so turns with it. The giant spring holds 15-555 firmly against the sprocket but if there is sufficient rotatonal force the cam lobes will slide against the spring pressure allowing some shock absorbing function.
Not sure if this helps......
01/05/2026 10:05:09 UTC
Ren - The Ed¹ said :-
So the sprocket "floats" on the shaft. It has 4 ramps that interlock with the 4 ramps on the splined item that has lateral movement but turns with the shaft and therefore the wheel. These 4 ramps of each piece are forced into connection with a big coil spring. If however there's sufficient shock in the transmission this causes the ramps to overcome the spring tension - a little. Hence the sprocket can move a little on the ramps and the spring absorbs the energy from the shocks.
Clever. I was thinking why don't we do that now but to be honest the modern rubber cush drives are cheap, effective and less complex. Oooh - how is the tension on the coil spring applied? I have horrible visions of having to force it into place with the associated loss of fingertips. I'm hoping there's a thread somewhere to build tension - I can see thread in item 67-1098.
05/05/2026 17:01:36 UTC
Ian Soady¹ said :-
That's right. It was a very common layout pre-war but later British bikes tended to have rubber inserts in the clutch centre and of course when alternators came in this type wouldn't work.
Re compressing the spring: that's what I was referring to in my earlier posts. I thought I was the one with memory problems.......
06/05/2026 10:11:41 UTC
Upt'North ¹ said :-
He's probably gone a hour without tea and biccies Ian.
06/05/2026 15:51:18 UTC
Ren - The Ed¹ said :-
You retired non working types have the mental space to put such matters together. I however have a very complicated job and a very little brain, theres insufficient processing power. That and a severe lack of tea and biscuits.
There is a solution to this problem. If you could all see fit to send me £100,000 each I'd be able to retire. Even with my small brain I ought to be able to keep up with the conversations once I stop working.
I'm too old to be learning new technology and programming languages. If you don't send me the money I'm going to end up out of a job anyway, or AI will replace me soon. Please hurry, I'm down to my last 100 boxes of 240 tea bags!
07/05/2026 08:08:41 UTC
Upt'North ¹ said :-
Ed, of course I'll oblige. You deserve it.
Please post you bank account and credit card details including your security and pin's and I'll get right onto it. You're welcome.
No what should I spend it all on?
Upt and Sincere.
07/05/2026 10:19:34 UTC
Ren - The Ed¹ said :-
What ya gonna do with the £3.64 that you could steal from my account Upt'?
07/05/2026 15:32:10 UTC
Upt'North ¹ said :-
Show off. Don't come on this ere forum for the aged flaunting your wealth. It's tough being a pensioner you know. I remember when you could go to the flicks, catch a PMT bus there and back and have a bag of tripe and chips in proper newspaper for 10 bob. Maybe even play around on the back seat of the bus too!
Tell that to the kids today and they won't believe you.
07/05/2026 17:11:24 UTC
Upt'North ¹ said :-
Made me think....yes I know....I shouldn't.
I'm sure the first pint of beer I bought in the late seventies was about 20p in new money. It would have been in Talke Working Mens Club in North Staffordshire, it had a great snooker room underneath the main building. Happy days, I was probably running a Gilera Trial 50 and petrol was 17 new pennies a litre.
Upt.
07/05/2026 17:19:34 UTC
Ren - The Ed¹ said :-
Goodness me you're REALLY old Upt'! When I were an 18 year old yoof my night out was a fiver. £2 of petrol into the H100A (2 stroke, this is what put me off 2 strokes). 2 quids worth of juice would see me right for a full week's riding. A whole £1 to get into Maxime's Rock Night in Wigan, leaving the remaining £2 for 2 cans of Coca Cola. I'd spend the evening failing to gain the affections of various "rock chicks" then ride home through the cold and the rain.
It was this time in my life I gave up drinking. The nights I was sober and failing with the girls were much more fun than the nights I got drunk while still failing with the girls. Sleeping in a warm bed sober is so much nicer than trying to sleep on Wigan Bus Station with a hangover.
Right - I have reviewed Ian's words and images re compressing the string. Now armed with the diagram and a better comprehension I can see the problem. This all leads me to be thankful I live in a time where we have hard rubber cush drives, it's a wonder anyone from the 40s and 50s has and fingers left!
08/05/2026 08:15:07 UTC
Ian Soady¹ said :-
20p a pint? Extortion. My first pint was in the High Force Hotel after a school walking club hike from High Cup Nick, passing the crashed Wellington(?) bomber up on the high fells and fording the Tees just above the waterfall. We must have been mad as any slip would have seeen us doing a Professor Moriarty. I remember the beer as being 1/9d (one shilling and ninepence) or about 9p in new money.
You lot don't know you're born although it's more recent in your memories than in mine.
In other news, visited a physio yesterday who confirmed I have a torn meniscus in my kne. Basically not much can be done other than exercise to strengthen surrounding muscles, and time. Maybe up to a couple of months of the latter....
Surgery is no longer recommended.
08/05/2026 10:15:18 UTC
ROD¹ said :-
I was about to respond but I thought Ian would trump me with lower prices for a pint.
My pints when first going decimal were 12p for special mild or special bitter.
I also seem to remember a conversation where people were saying that they would stop driving when fuel reached £1.00 per gallon!
I hope things improve with your knee Ian.
The doctors advice to strengthen surrounding muscles sounds good.
08/05/2026 12:03:11 UTC
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