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Ossa 280 Gearbox problem


Ossa2011
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Hi,

I have been having problems with my gearbox on the ossa.  It started a few weeks ago where I couldn't change up from 2nd to 3rd.  The gearbox came out and the selector drum was worn where the rollers turn it.  I replaced this and rode last weekend.  I managed to get into all the gears, but it needed repeated attempts to change.  Also I noticed that there was a vibration coming from the gearbox.

I now have the gearbox out again and notice how much movement the drive shaft (sprocket) has.  It will lean left and right and also the shaft itself will move up and down.  I wonder if this is normal? What holds it at the bottom (opposite end to the sprocket)? 

Now comes my new problem.  When I put the gearbox back into the bike and tighten the 5 screws then the whole gearbox locks up and nothing will turn.  If I put it in loosely I can turn the sprocket by hand and click up through the gears.  However when changing I notice the sprocket moving in and out of the casing and then everything locks up again.

Any help will be gratefully received.

Regards,

David

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A few things to look at here. Is your bike a 2011 model? Do you mean that the selector drum was worn where the indexing roller runs in? The shaft with the sprocket on is the secondary shaft, On the primary shaft, is this held in place with a through rod and left hand threaded nut? If not, the primary shaft has a tendency to work out from its LHS bearing and create shifting problems as well as allowing the clutch basket to gouge into the housing. Let me know if the primary shaft is secured in the bearing or not. When the gearbox is correctly assembled into the crank case, there should be no real discernable axial movement. However, when out of the crank case there is nothing to prevent axial play. Nothing holds the secondary shaft in situ at the inner plate end to prevent axial movement, this control is provided by it's fit inbetween the bearing in the LHS and the gearbox inner plate. It is easy to assemble the gearbox into the crankcase slightly wrong, have a look to see that the sprung loaded indexing arm/roller is properly located into the drum, you must be in gear to assemble the gear set. Are you tapping the clutch to ensure the primary shaft is home? I think that will do for now. Bye, Peter.

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Thanks for that Peter, my Bike is a 2011 and so it doesn't have the rod to hold the clutch basket in place.

The good news is that I have managed to get it all back together and it works :-).  Along the way I learnt a few things. 

My main problem was that I would install the gearbox with the 5 screws finger tight.  Then I would test the gearbox by sliding the sprocket onto the end of the shaft turn it whilst clicking up through the gears.  However I hadn't installed the collar between the sprocket and the casing.  The secondary shaft would then move in and when I changed gear again everything would bind up.   I would then take it all apart and try again.  The problem was right before my eyes, but I just couldn't see it.  After posting to the forum, having a coffee and talking the issue through with a friend then it became clear.  So the moral of the story is never click up and down through the gears without installing the sprocket collar.

Whilst on the bench I also noticed that the centering spring under the roller was slightly off and this had the effect of not allowing the rollers to return to the correct position between gears.  A slight turn of the centering nut fixed that.

When installing the clutch I had to put a piece of wood across the top of the clutch basket and tap that with a mallet until everything was seated.

The vibration the bike had a week ago is also mysteriously gone.  That worries me, but the bike is riding great again.

 

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