Burman Gearbox anomaly

[Davidmeachen]

The Gearbox on my 55 Huntsman seems to be a bit odd! The gears are: 1 up and 3 down with neutral found between 1 & 2. However, I also have a full neutral between 3rd and 4th gear. Not knowing anything about 57yr old Burman gearboxes I am hoping that one of AOC members can shed some light. Also, there seems to be quite a lot of travel on the actual gear-change lever when changing to any gear. Any advice would be appreciated

[pete.collings]

The pins that fit through the selector forks and into the selector drum can frequently wear, which gives more backlash when selecting gears and would increase the travel on the gearlever. The arms of the selector forks can also wear, although this is less common and often due to keeping a foot on a poorly positioned gearchange lever. The gearchange shaft can also wear, as it is a steel shaft running in a steel bush. Wear in the bush is less frequent, at least that is my experience. The detente plunger/spring behind the selector drum can also wear, lessening the positive selection/retention of a gear. If they need replacing, I can help with the selector forks and gearchange shaft, but not the selector pins, send a PM for more details.
The GB Burman boxes do have a bit of free play, the false neutral you descibe may be as a result of excessive play, or possibly wear on the locating dogs on the gears themselves. If the problem is too great, a full gearbox stripdown is in order, it is just about possible to remove the gearbox without removing the engine, although this involves extensive slackening of engine bolts/plates and manouvering of the gearbox. The gearbox outer and inner covers can be removed with the box still in place, although this makes removing/replacing the gears/selector shafts a bit fiddley.

[Davidmeachen]

Hi Pete
Thanks for your advice. The bike is going for DVLA inspection on Wednesday and after that I will take the gearbox off and see how far I can get in checking the items you have mentioned. If gaskets are required, would you know if they are of the paper type? If so I can purchase gasket paper and make my own.
Regards
Dave

[pete.collings]

Hi Dave

I never used gaskets when I rebuilt a GB gearbox, instead prefering to use a thin smear of silicone gasket on one of the mating surfaces (fully cleaned before application) and allowing it to set overnight before assembling the gearbox, with a smear of oil on the mating surface. This allows the joint to be disassembled without loosing the silicon layer, provided you are careful! This method is also useful on the primary chaincases (which will need removing if you are to remove the gearbox from the frame), and can also be used with engine mating faces, although here one has to be careful that only the minimum amount of silicone is applied, to avoid any loose material entering the oilways. Applying the silicone towards the outer edge of the mating surface would help any excess to squeeze outwards, where it can be removed.
Other people may prefer the use of the paper gaskets when rebuilding gearboxes, the only effect of omitting them is to slightly lessen clearance, especially in the outer part of the gearbox. Try dry assembly with everything fully tightened, and check there is no stiffening of lever movement as the outer cover is tightened. If there is, then ease the bush surface where the contact occurs, the bushes can be removed by warming the case and drifting them out (with a correct shaped drift!). If new bushes are fitted (or a different end cover fitted), checking the clearance is essential, the bush in the outer cover for the selector drum can often foul the drum, giving a very stiff gearchange action.

[Simon.Gardiner]

I've yet to have a Burman box where you couldn't find more than one neutral (OK so I've probably only owned half-a-dozen) and I can confirm that the box on my airhead BMW has 4 neutrals in it when you're trying to work it through the gears by turning the back wheel!

I think jumping out of gears/not selecting gears will be more where the problems are....

[Davidmeachen]

Thank you Pete.collings and Simon.Gardiner for your advice. I too will use a silicon gasket when I open up the gearbox and thank you Simon for letting me know that more than one neutral is not unusual on these vintage gearboxes

[keith.mettam]

Hi David,
If you are interested, both paper gaskets are available from DraganFly for around a couple of quid. The following link shows their exploded parts drawing and references :-

http://www.draganfly.co.uk/images/shop/14/19GB.gif

I personally would fit the paper gaskets. The choice is yours of course !
Have fun with it, they aren't too bad to work on once off the bike and on the bench (with the aid of a good vice to hold the box in).
Keith Mettam.