Author Topic: Dragonfly gearbox  (Read 3002 times)

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Offline davrhos

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Dragonfly gearbox
« on: 23 Dec 2014 at 11:17 »
Seeking help/advice on my D/fly gearbox problem.  Have owned bike, and ridden it, for around 40 years but have never been able to sort out problem with gear change.  Box has always been noisy and 'crunchy' when changing down gears, and also to some extent when going up the box, but is now at the stage where it is really uncomfortable.  The only way to get a clean gear change is to forget the clutch and go 'clutchless'. 
     I've stripped the box, checked all the gears for wear, replaced any suspect bearings, different oil grades and levels,made sure all fasteners are tight but without success.  The clutch works perfectly, with no drag when lifted.  With the bike on the stand and a gear selected the rear wheel can be spun by hand with the clutch lever lifted, so can't imagine a problem in that respect.
     The only thing I haven't done is to try new selectors.  Could this be the problem.  When I stripped the box I couldn't find my spare pair to try, and then realised I'd sent them some years ago to a club member for re-furbishing, and didn't receive them back.  Trouble is I can't remember who it was.
     Would appreciate any help or advice.  Merry Christmas to all, and Happy New Year.

Offline eddie

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Re: Dragonfly gearbox
« Reply #1 on: 23 Dec 2014 at 12:12 »
Hi,
      The problem may be partly selector related as it is gradually getting worse - this would suggest that whilst there has always been a problem, it is being compounded by wear. Dragonfly gearboxes seem to suffer from poor quality control regarding the machining tolerances - resulting in some gears (say 2nd gear) having a deep mesh on the dogs at the expense of the mesh on 3rd gear. This can be rectified by either shimming the layshaft to bring it forward or grinding some off of the face of the layshaft 1st gear pinion to let it move back to equalise the depth of mesh on the respective dogs. Some Dragonfly 'boxes also suffer from shallow engagement of top gear - resulting in them having a tendency to jump out of top gear. This can be improved by dismantling the input shaft and bearing assembly and inserting a shim behind the outer track of the bearing and then reassembling. This will result in the outer track standing proud of the face for the square retaining plate, so the same thickness shim will be needed under the plate so that it will tighten securely without distorting and cracking the plate.  There is seldom any problem with the mesh of 1st gear, and in any case, it is rarely necessary to engage it whilst on the move so can be selected in a more leisurely manner.  With these checks/modifications done, the gearbox should be improved enough that any selector wear will have little effect on the quality of the gearchanging.
  With regard to lubrication - I have always used SAE 40 oil in my Dragonfly 'box. I am of the opinion that Douglas only specified SAE 140 as means of obtaining a slightly quieter 'box - not to improve the actual operation of the 'box.

  Regards,
                Eddie.

Offline davrhos

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Re: Dragonfly gearbox
« Reply #2 on: 24 Dec 2014 at 15:01 »
Thanks for that Eddie, sounds rather complex for a layman, though I do understand your reasoning.  What I can't understand, trying to think logically, is why when clutchless changes are made the gears engage easily and quietly, yet the problem arises when the clutch is used.  Yes I know with a clutchless change you are matching the engine speed to that of the gear selected, but the fact is surely, if the change is noiseles it must indicate that the cogs are in decent condition,or am I taking logic too far. 
     I think maybe, not having the knowledge or expertise to delve too deeply into your suggestions, I'll try new selector forks ( if the Club have any) and if that doesn't work then I'll be back.  Thanks again for your help.

Offline eddie

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Re: Dragonfly gearbox
« Reply #3 on: 24 Dec 2014 at 16:57 »
Hi,
     The changes between 2nd and 3rd (either up or down) are the ones that seem to be most affected by too deep a mesh on the dogs. With the extra depth of mesh plus a little wear, one gear may not be fully disengaged before the other takes up - thus causing 'crunchy' gearchanges as the shafts and gears don't have time to adjust to the new ratio. With clutchless changes, you are keeping the drive train in tact and manually synchronising the speeds to get a smoother change. With regard to new selector forks - I don't think the Club has any in the spares. Providing the rider hasn't tried to keep the box in gear by keeping his/her foot on the gearchange, the forks don't tend to wear too much - the biggest problem is wear to the pins that locate in the camplate - but these can be built up with Stellite and reground.

  Regards,
               Eddie.

Offline davrhos

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Re: Dragonfly gearbox
« Reply #4 on: 25 Dec 2014 at 12:04 »
Me again,
Thanks Eddie, have e.mailed Dick and will see what he says about availability and work from there.  Anybody made an Auto' box for Fly?
Best Wishes,
        Dave.

Offline eddie

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Re: Dragonfly gearbox
« Reply #5 on: 25 Dec 2014 at 13:23 »
Some of the 'boxes come pretty close to it!! They've definitely got a mind of their own doing what they want, when they want!!

  Eddie.