Thread: New Oldham for the Panther

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I have a 650cc Panther motorbike that was made in Cleckheaton, England in 1964.
It has an unusual but handy feature in the form of an Oldham coupling to drive its magneto/dynamo.
It's great to be able to remove or replace the whole ignition and charging system in a few minutes.
However, the coupling has what I believe is a design fault. Earlier Panthers were fitted with a
conventional, cruciform type of Oldham coupling which worked fine. At some point they changed to a simpler, square type.
The square type has driving faces that are much farther apart. This does two bad things:
- The "angle of attack" isn't as good, which makes the fibre centre piece wear rapidly.
- Wear translates to more play than would be the case if the angle wasn't as great.
It can't be good for ignition timing, which on mine had play equal to more that one whole tooth on the
gearwheel. But as these bikes still run and perform adequately in this condition, owners put up with it.
But it's just not nice.
Unfortunately the earlier type can't be fitted directly to my newer bike.
Good news is that all these parts are available new, so I only had to modify half the coupling, as the
other half could be fitted straight onto the magneto.
I haven't run the bike yet due to other problems (needs new valves and guides) but when I put a
very second hand, worn, cruciform type of fibre centre piece in it, play is much reduced.
I took photos and documented the modification process after a request from forum member Anorak Bob.

Jordan


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Magneto showing the later type of Oldham coupling fitted, as original to my bike.
It's mating piece is in front, with a worn fibre block. It's the engine's magneto driving gear shaft.
Note that it has a large hole drilled in the centre which is quite deep, that can be used for the modification.
To the right is the preferred, older style of Oldham that will be attached to the magneto.
I need to modify the gear shaft to be able to mate with the new "old" coupling.

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On the left is a driving gear shaft from an earlier model Panther.
It has different dimensions, so can't be used on my later engine.

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The flange with the Oldham drive is removed from the existing drive shaft.
Brass shim protects the bearing surface from the chuck jaws.

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Flange completely removed.

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4 jaw chuck holds a piece of available steel, from which the new Oldham piece will be made.
The scrap was once a sledge hammer head.

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The back of the new part, that will be fitted to the front of the original shaft that had its flange removed.
The extended bit will be fitted to the hole in the original shaft with retaining compound.

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The two pieces to be joined together, temporarily fitted.
The large diameter has been turned, to be able to centralise when it is turned about to finish the other side.

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New flange in 4 jaw chuck.

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Centralising in the 4 jaw chuck.

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Parts to be chemically joined.

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After the parts are chemically bonded together, the assembly is put in the 4 jaw chuck to centralise
off the bearing surface. This ensures the features to be machined afterwards are true to the shaft.

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Faced surface is centre drilled to provide clearance for a boring bar to enter.

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Starting the boring to the required shape before milling the coupling dogs.
The outside diameter has also been turned to finished size.

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Boring completed to required depth.

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Milling setup.

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Starting the milling, full depth, half a millimeter per pass. Yawn.

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One side done, other side in progress.
Nice and parallel, by just moving the Y axis.
The mill's handle dials were used to control dimensions, which worked out well.

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Complete part.
That's the original driving shaft that has had its "square drive" coupling removed, and replaced
with the cruciform shape.

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Finished Oldham assembly, with cruciform centre piece.

Nice work Jordan.

Nothing beats having the right gear to execute a repair. Never knew you had an FB-2!

Bob.