Dragonfly Gearbox failure

[steve.link]

Just completed my full restoration and now have a disaster in the gear box - see attached photos.
Anybody had this before and can advise/help?
Looks difficult to access for welding. Is anther gearbox casing the only solution?

Thanks

Steve

[eddie]

Steve,
          That is not un-common on a Dragonfly gearbox. That auxiliary shaft is also supported by the round plate in the back of the gearbox (below the swinging arm). You will probably find that half of the support boss has broken away on that as well, as it has a slot milled across it. The slot locates a cross pin in the auxiliary shaft to prevent it turning. I think it would be better, and stronger without the cross pin and slot - the shaft will only turn when the kick start is operated - while the engine is running, the kick start mechanism is disengaged, and stationary.  As an attempt to effect a repair, you may be able to get the broken piece tack welded into place. Then Araldite a sleeve over it to provide some reinforcement (make sure you use the original 24 hour Araldite - Araldite Rapid is rubbish!).

  It is possible to get the gearbox out without disturbing the engine - remove the toolbox (3 bolts), take out the swinging arm pivot bolt and move the swinging arm back. The gearbox can then be disengaged from the engine, and can be lifted out.

  Regards,
                Eddie.

[steve.link]

Eddie - thanks!

Been rummaging through all my old bits and pieces and I have found another gearbox casing which looks ok. I will clean it up tomorrow and have a better look at it. So are you suggesting to remove the cross pin when I assemble the replacement gearbox?

Steve

[eddie]

Steve,
            As you have found, there is an inherent weakness in the Dragonfly gearbox (which can render the main casing totally useless), and my previous suggestion was aimed at recovering the original case. However, if you have a better replacement case, then build everything into that case, but take on board that the original weakness still exists. The most likely sequence of events with your original box was that the auxiliary shaft rear support fractured, operation of the kickstart then levered the auxiliary shaft out of the lug in the main casing. So, to prevent it re-occurring, do a dummy run of re-assembling the auxiliary shaft and the rear mounting plate, with a view to strengthening the mounting plate with a run of weld down the outside of the slot (with a bit of luck, there will still be room to fit the cross pin - if not, leave the pin out).
     Before finalising the re-assembly of the box, check the mesh of the dogs in all 4 gears (especially top gear) - some of the later Dragonfly boxes suffered from shallow engagement of the dogs causing the bike to jump out of top gear when under load. This can be easily overcome by shimming the input bearing - get back to me if you need more help on this,

   Regards,
                  Eddie.

[steve.link]

Eddie

Thanks - will let you know if I get stuck!

Steve

[steve.link]

Hi Eddie

Found 3 old gearboxes in the back of the shed and 2 have the same broken casting - so it is very much a common issue. Luckily, I have got one good one which I just stripped down completely apart from the kick shaft bush. I tried to drift it out but it doesn't want to move and I don't want to risk breaking the only good case I have. There is no felt washer in the bush and was wondering if a rubber "O" ring could be installed instead?

The round plate at the back of gearbox is also damaged so I will need to get that welded up as well. At least I have a way forward but very annoying on a bike that has just been restored!

[steve.link]

Just been thinking about this auxiliary shaft housing failure and it seems to me that the orientation of the cover could contribute to a failure. As it has 3 fixing screws there are 3 possible ways to fit it to the gearbox. On my example the crack seems to be starting at the point of contact with the locating pin in the shaft (photo 1). If the cover was fitted as in photo 3 the pin would be vertical and not be able to put much force onto the boss.

I am getting the slots welded up and removing the pin so not to have this issue again

[steve.link]

Can anyone tell me the size of the larger ball bearing (LH) on the gearbox final drive shaft. Its item 7 on Plate 17 of the Dragonfly parts book (Part No 19304)

[eddie]

Hi Steve,
                According to our list, Part Number 19304 is a  6205 bearing (25mm x 52mm x 15mm).

   Regards,
                 Eddie.

[steve.link]

Thanks  Eddie - any thoughts on the orientation of the cap for the kickstart auxiliary shaft?

Steve

[steve.link]

Lets see if this works any better?