Ossa tr280i Gearbox removal proplems

[Watty82]

Hi, I recently bought a 2011 tr280i. The bike looks in good condition but seems to shift into gear by itself while the engine is running. 

So I'm trying to pull the gearbox out to inspect. I got the five bolts out and have it in gear but it just doesn't seem to move with a tap on the output shaft. It seems like the clutch shaft is jammed somehow. 

It doesn't have a clutch fixer nut because it's 2011 so I really need some advice of how to remove it. 

Cheers. 

Edited November 17, 2018 by Watty82

[canada280i]

You are positive that the clutch fixer rod has not been added?

[Watty82]

Yes definitely no fixer rod, I can see straight though to the breather. 

I'm wondering if the clutch shaft could be somehow stuck in the bearing. I might try a large expansion bolt in the clutch shaft so I can pull from there. 

[lotus54]

So you got all 6 bolts?  

 Ha- just kidding, I now there are five.  There is a circlip on the countershaft- no?  I can’t remember.  You may want to use a heat gun on the countershaft bearing area to help loosen?  But no flame and not too hot.

Mine has the fixer nut and once I got that off it came right out. (The original instructions didn’t mention that, so had me on the run a bit).

[ric h]

My 2011 is different.But i seem to recall hearing about the fixer nut being left hand thread and hidden inside.Thoughts?

Edited November 17, 2018 by ric h

[Watty82]

Thanks for the replies. I wish there was supposed to be 6 nuts. 

The only circlip on the countershaft was to remove the sprocket. 

When I tap the countershaft with a rubber mallet it seems like the countershaft moves and isn't the problem. It seems more like the clutch shaft is stuck, almost like it has a fixer nut although it definitely doesn't. 

Could it be that the clutch shaft has some how stuck to the bearing in the crank casing. So when I hit the countershaft it twist the gearbox. 

Somebody must have experienced this problem before. 

[pauls320]

https://birkettmotosport.com/application/files/4015/1387/5661/Ossa-Transmission.pdf

[ric h]

@tsiklonaut   He may know more about this problem

[Watty82]

Cheers for all the input, thanks for the link but I've already been through it several times and I haven't missed anything.

I'll try to find a suitable expansion bolt from work tomorrow to fit in the clutch shaft. Then make some kind of slide hammer from it which will hopefully work to dislodge it. 

[canada280i]

Or you could remove the gearbox vent and insert a thin drift to gently tap the shaft out of the bearing seat.

i wonder if you will find that someone has previously had the box out and thread locked the shaft into the bearing to stop the float that the clutch fixer shaft fixed.

Edited November 18, 2018 by canada280i

[Watty82]

That's a good idea, I'll give it a try if I can't find the right sized expansion bolt. 

Maybe the shaft has been loctited in place, I'll report back when or if I eventually remove the gearbox. 

 

[peterb]

As canada280i said, it is very likely that the primary shaft has been loctited in place, to prevent the shaft from working out of it's LHS bearing. They do come out ok even with loctite, you should be able to tap the cluster out by tapping on the output shaft and the gear selector shaft, lightly with a hard rubber mallet. With it dropping into gear, it's possible that the selector shaft spring has failed, or one of the end arms of the selector shaft has broken. If light tapping doesn't work, you will need to make a plate that is drilled to the BCD (Bolt circle diameter) of the clutch centre bolts, use the 18 bolts to fix this to the clutch centre, and use your favourite slide hammer to extract the primary shaft as you tap the output shaft (not at the same time though!) Bye, Peter B.

[Watty82]

Thanks for that Peter. I finally got the gearbox out using an expansion bolt and slide hammer. It didn't take that much force in the end, just alternating hits between the output shaft and clutch shaft. 

Luckily the gears all seem OK except some slight wear on the idler gear. 

The selector drum notch for neutral seems really wore, maybe this is the reason for dropping into gear. I was thinking of machining the notch a little more to help keep in neutral. 

The two bearings inside the engine casing seem a bit gritty so might replace them and install a clutch fixer rod at the same time. Are they pretty standard bearings? 

I will probably also drill an oil hole in the gearbox plate to help oil draining. 

Both the output shaft and clutch shaft seem a bit loose (side to side movement), is this normal? because it seems like a big job to replace those bearings. 

Is there any other mods that I should do whilst the gearbox is out? 

Thanks for all the help, Matt. 

[peterb]

Hi Matt, When the idler gear stub shaft bush wears considerably, this creates a whining noise, most noticeable when in 2nd gear. The neutral notch indent shape was changed on later drums to provide a more positive location. The wear on your shift drum is not bad, it's hard to escape the wear as the spring tension on the cam follower wheel is really strong and the wheel width is quite narrow. I would not machine the neutral position on the drum, the wall thickness there is really thin and you would machine through the hard surfacing, I can't remember if these were ENC plated or plain hard anodised. The wear shown on the drum would be insufficient to allow the gearbox to drop into gear. It is likely that either the cam follower return spring has weakened or the selector shaft position spring has failed or is not in the correct position. The selector shaft position spring is set up using an eccentric adjuster to allow the shift rotation to move the selector forks the correct distance in both directions, up and down the gears. It's not easy to set up either. In essence, there should be a lot of tension on both the cam follower spring and the selector spring.

Yes, drill a 4.5mm oil hole in the gearbox plate, at it's lowest point, you can see it, right in the corner.

When the gearbox is in place, there is radial play on both shafts, more so on the primary (clutch) shaft, excessive play on the secondary shaft is due to the idler gear stub shaft bush wearing, these can be replaced. We modified the gearbox plate idler gear bearing housing, drilling a 2.5 diameter hole through the top of the housing, counterbored half way down with a 4mm diameter drill to provide an oil well and feed system for the bush, also ground grooves into the shaft bearing areas to allow oil to enter and leave the bearing areas, probably a few more things to make the gearbox last that I would have to think about. With the gearbox out of the case, the shafts flop around like you would think they were never going to work.

Have a look at the end of the primary shaft, the left side where it fits into the bearing, the shaft was modded by machining about 6 little dimples to provide an irregular surface for keying in the loctite. If there are non there now, they are easy to grind in with a small die grinder or Dremmel type tool

You are not able to install the later model clutch fixing bolt, there is insufficient metal behind the LHS bearing to do this. From 2012 onwards, the crank case was changed in this area to provide clearance for the bolt. Bye, Peter B.

[Watty82]

Really appreciate all the info Peter.

I'll dremel the notches into the end of the primary shaft. The bearing that the primary shaft slots into doesn't seem to have a circlip holding it in place, I thought it was supposed to have one.

I'm very interested in doing the gearbox plate idler gear mod with a Delrin bushing, although I'll get the bike back together and see how it rides first.

Both the cam follower return spring and selector shaft position spring seem in good condition, so I'll try to fine tune the eccentric adjuster. 

I haven't had a trials bike in over 20 years so I'm really exited about getting out on this beast. I've been riding enduro but the trails in Finland are really technical so I think a trials bike would be way more suitable. So I'll be restoring the Ossa ready for Spring.

Thanks again, Matt.