Hi all,
I am in the process of rebuilding my 1938 16h dolls head gearbox and have noticed the following anomaly with the linkage or actuating rod that appears to make little sense.
As the quadrant plate arm turns on its axis it naturally moves outward as it reaches a horizontal position 9 0clock and then back inward as it heads either down or up. The bottom Clevis pin and link are able to pivot at this point, but the upper clevis cannot and can only cater for movement toward or away from the gearbox casing. This results in stiffness and strain on the top clevis when at or around horizontal. I can only see tig welding or threading a rose joint on to the upper arm or engineering sideways slop on the upper pivot to alleviate this problem. As it stands all links are smooth and snug so it seems a shame to compromise on this.
Is this a new one or has anyone come across this before.
Regards,
Rodge.
Somerset, England
It was surely just an…
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Thanks David, I am acutely…
Thanks David,
I am acutely aware that the 16h was a tool for a job and banged out for the war effort to cost. They are lovely old bikes and their agricultural nature is part of their charm. It does seem an odd way to do things though.
The box I have appears to be unmolested but detailed information about their function seems thin on the ground unlike my BSA. I guess I will have to loosen the upper clevis by 50 thou or so and be at peace with any slop.
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Gearbox linkage.
Hi Roger,
The Sturmey Archer gearbox that the Norton gearbox is based on had a double clevis on the top joint as this issue was recognised in the original design. Unfortunately the company went into liquidation in 1934 and Norton took up the design and modified it to their requirements, some of which may have been financial. Although the linkage is primitive in design, over 120,000 were made and the Norton/Burman gear-change was considered the benchmark in it's day. Don't be too eager to loosen it up as most of the problems come from worn linkage resulting in only getting 3 of the 4 gears. Make sure there is plenty of sideways gap in the clevis fork to make this poor design work.
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Gear actuation
Thanks Richard,
I would never have found that out trawling the net. I will come to a compromise with it I think and keep it as untouched as possible.
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You could....
... make up a linkage using rose joints for riding and replace it with the original for showing......
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I could I suppose but I don…
I could I suppose but I don't see any other threads on this so it's clearly not some common complaint, and as stated by others they can be a nice gearbox when well set up, so I reckon I will do minimal to it.
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It was surely just an engineering compromise. If the links and top clevis is made to fine tolerances it will not work without twisting the top lever. But unless someone has made it with tight tolerances, the top clevis will have enough slack to allow the bottom of the rod to wobble in and out easily. It's a variant on the old adage - the engineer can make it work for a penny (when the craftsman would do it for a pound...)