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Gearbox dog rings

As I have a couple of gearboxes apart in poor condition and wanting parts I thought, just for fun I would draw up some dog rings.

The original parts have kindly left many witness marks behind suggesting the original design was flawed.

Now having a CAD solid model it clearly proves it is. Neither the slopes of the "roof" or the dog faces are in full mesh as they slide over their corresponding face. I had a play with simple tool path corrections and managed to improve it, but not correct it. Unfortunately it requires a 3D profile. Far to expensive to make as know one would pay for it. The dog face isn't as bad and as long as you have full engagement the faces should match.

One thing for sure is that the gearbox must have a magnetic drain plug to ensure long bush life.


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Re: Gearbox dog rings

Early dogs and the corresponding gear faces had a flat form, being changed to the 'pent roof' form to improve selection...Witness marks on the dog teeth are inevitable as the dogs do not select 'cleanly' but are assisted by inertia to engage. Contact is therefore inevitable before engagement...
This is exacerbated by incorrect assembly and/or setting of the box, a condition that frequently occurs as the correct assembly methods are not immediately obvious...I'd say just about all examples have been affected by this at some point, so damage is bound to accrue beyond the 'normal' levels...
WD boxes are also very prone to oil loss as no modern seal was fitted...This is made worse by regular use of the field stand...

The oil level can drop to critical levels in only a few hundred miles and in the days when people didn't bother to lavish maintenance on a 'cheap' ex WD machine this led to more wear prroblems....
At the end of the day this was a hand change box that had footchange added to it and is pretty typical of many gearboxes of the time...A notable exception was Triumph who were already producing a cam operated box by 1936...BSA were well behind...
It's remarkable though, just how robust and durable these boxes are despite their 'backward' design...In fact when assembled and set up correctly the gear selection is entirely acceptable, despite it being a very 'slow' box due to the size and inertia of the gears when running....It can also take some time to appreciate all the relevant points that require attention..Ian

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