Friend's 2012 Ossa TR280 got stuck in 1st gear after a crash, so we decided to help him try and remove the "5" 3mm allen bolts holding the cassette transmission/clutch assembly. We finally got all 5 bolts out, but now we are puzzled by some reference to "clutch fixer nut". Removed crankcase breather elbow from just in front of front sprocket and not having any luck to figure out how to secure a hollow passageway to remove LH-thread fixer nut, or even where it is located. Has anyone else ever pulled Ossa cassette transmission & what did you do to remove after 5 bolts are out? Tried hitting countershaft (with sprocket removed) with dead blow plastic mallet, but shaft seems like there is another step we are missing...

Clutch fixer nut is in the centre of the clutch basket. To secure it use a torx wrench pushed through the crank breather hole, give it a tap to secure it on the clutch fixer rod hole and then undo the left hand nut

if you gave an early 2012 you may not have the nut as the rod was an upgrade on the 2012 model

Edited May 10, 20179 yr by canada280i

Just a bit more to add to the above. The Torx cut/pressed/stamped into the end of the clutch securing bolt was never very well performed and you may find that a T10 or T15 Torx key is needed to hold the bolt. The LH threaded nut needs a 12mm socket to undo. It was never intended to be very tightly nipped up as the bolt is hollow and easily sheared off. Use a dab of blue loctite on this thread when re-fitting. Don't over tighten.

If it's stuck in first gear, the selector shaft is likely to be broken at the "pawl" end, bit weak there in the early bikes. And/or, at the worst case - the selector drum has been cracked, maybe not so easy to find a new one. Have a good look, it can be just a hairline crack.

When re-assembling the gearbox, it must be in a gear, not neutral as it won't go back in the case. The cluster usually fits back no problem, needing a few light taps on the clutch to ensure it is home. Clean the oil off the 5 shouldered 3mm hex allen bolts, only use a dab of blue loctite on the ends of the thread. Best allen key I found was made by Beta Tools, Italy, no relation to the bikes, these are what the factory used to use. Get the all steel Tee handled 3mm wrench. Look out for the 2 x 25 OD O rings fitted to the outfut shaft sleeve, if only one fitted, there is a good chance of leakage from here.

Bye, Peter B.

Thanks for the replies. This must be an early 2012, because it doesn't have the newer design that includes fixer nut. Found a couple pieces of shifter drum and/or shift shaft pawl that broke off. Some abnormal wear on the clutch drive/driven gears and seems like a good job for an OSSA Shop like LewisportUSA.com - assuming that parts are still available somewhere.

I understand Lewisport has a jig used in transmission reairs- and I believe have been sourcing parts etc.

  So far, most stuff seems available (stuff like stickers and some plastic not so easy)

Some changes were made to later transmissions- it may be good to see if any upgrades could be made at the same time.

  Mine at over 330 hours is still working great.

Later selector shafts were designed/built stronger, same for the selector drum which had more material around the indexing area. It would be unusual for the clutch outer drive ring to wear, do you mean the idler gear behind the clutch basket? This is the gear that is engaged by the kickstart pawl, the 5 tooth gear or quadrant. The idler does wear. There were 2 gearbox suppliers, best one was from Italy the other from Spain. The Spanish gears were machined on the OD plus a few more problem areas that were introduced. To determine which gear set that you have, measure the OD of the idler gear, if 50.80mm or less, it is Spanish, if 51.30mm then Italian. Lewisport would know of this.

When you do re-assemble into the crankcase, seeing that you do not have the clutch through bolt system, the LHS of the primary shaft needs to be loctited in position inside the LHS bearing. Prepare the end of the primary shaft by grinding dimples around the outer shaft surface, to provide a keying surface for the loctite. If not loctited in position, there is a chance the shaft will move outwards, with resulting gear damage likely.

Bye, Peter B.