scotty Posted July 10, 2007 Report Share Posted July 10, 2007 Im trying to sort a problem weve an ossa engine ive got up and running it starts up ok, and 1st and 2nd select ok and the bike pulls away normally BUT wont shift into 3rd gear! anyone had this problem? the gearlever not bent and the bike selects 1st and 2nd going up and down the box when riding it but no 3rd gear and upwards! HELP!!! Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 10, 2007 Report Share Posted July 10, 2007 Are you able to move the gear selector (up, I assume) after 2nd gear or will it not move at all? Quote Link to comment Share on other sites More sharing options...
scotty Posted July 10, 2007 Author Report Share Posted July 10, 2007 no the gearlever wont move up above 2nd gear! thanks! Quote Link to comment Share on other sites More sharing options...
andy m Posted July 10, 2007 Report Share Posted July 10, 2007 Has the motor been apart. I had a similar problem, not Ossa but the selector shaft was not put back in the correct position where teeth engage with the selector drum, too high i think and would not go past 2nd gear. If its possible you need to push the shaft out and go down a notch on the drum. A lot of hassle I know but it sounds as if thats it if the motor has been apart recently. Good luck. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 10, 2007 Report Share Posted July 10, 2007 I don't know if they have a drum selector like a Bultaco, but that is one place to start. Or a broken fork. If you were looking for an easy answer without splitting the cases... Quote Link to comment Share on other sites More sharing options...
woody Posted July 10, 2007 Report Share Posted July 10, 2007 It's impoosible to diagnose really, there is nothing specific about an Ossa gearbox that I can recall that could cause this. The fact that 1st and 2nd can be selected suggests the selector mechanism and the selector fork that engages the drum are okay as it engages up and down. Sometimes the tips can break or wear off the end of the fork that engages with the pis on the drum but that usually reults in a moving gear lever but no selection, rather than a jamming lever. If it is jamming when trying to select 3rd then it could be a bent selector fork (ie; one of the forks that slides the gears not the selector drum fork) or maybe something has broken in the gearbox, like a tooth, and there could be a bit of metal jammed in the slot in the selector drum that the 3rd gear fork uses. It could be anything really, even incorrect shimming as the Ossa relies heavily on shims to get the gearbox to work smoothly - they are on most shafts and on either end too. When engines are stripped they sometimes get thrown back together without any shims and it is pot luck whether they work well or not. Some will, some won't. Was it working ok before and has this just happened or is this the first time you have run the engine and found there is a problem. If the engine has been apart, incorrect shimming could be a possibility. It isn't possible to get anything out of alignment on the selector mechanism with the selector drum, it will only go on one way. If the spring on the selector shaft was not located properly it is unlikely you would get both up and down selection, usually just one or the other - not impossible though so that is also a possiblility, although remote. Unfortunately, all of the mechanism is in the gearbox so you have to strip it to see if anything is wrong, no other way really Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 11, 2007 Report Share Posted July 11, 2007 It's impoosible to diagnose really, there is nothing specific about an Ossa gearbox that I can recall that could cause this. The fact that 1st and 2nd can be selected suggests the selector mechanism and the selector fork that engages the drum are okay as it engages up and down. Sometimes the tips can break or wear off the end of the fork that engages with the pis on the drum but that usually reults in a moving gear lever but no selection, rather than a jamming lever.If it is jamming when trying to select 3rd then it could be a bent selector fork (ie; one of the forks that slides the gears not the selector drum fork) or maybe something has broken in the gearbox, like a tooth, and there could be a bit of metal jammed in the slot in the selector drum that the 3rd gear fork uses. It could be anything really, even incorrect shimming as the Ossa relies heavily on shims to get the gearbox to work smoothly - they are on most shafts and on either end too. When engines are stripped they sometimes get thrown back together without any shims and it is pot luck whether they work well or not. Some will, some won't. Was it working ok before and has this just happened or is this the first time you have run the engine and found there is a problem. If the engine has been apart, incorrect shimming could be a possibility. It isn't possible to get anything out of alignment on the selector mechanism with the selector drum, it will only go on one way. If the spring on the selector shaft was not located properly it is unlikely you would get both up and down selection, usually just one or the other - not impossible though so that is also a possiblility, although remote. Unfortunately, all of the mechanism is in the gearbox so you have to strip it to see if anything is wrong, no other way really I think I said all of that in about two sentences. Quote Link to comment Share on other sites More sharing options...
scotty Posted July 11, 2007 Author Report Share Posted July 11, 2007 Thanks everyone! dont think the engines been stripped! its just a fault thats occured? Woody it looks like the engines gonna be striped down! best watch out for all of them shims dropping out all over the place! (if there is any! ) incidently apart from a air wrench to shock the left hand thread flywheel nut off! Dont you also need a special splitter to get the coller of the over side of the crank??? where do you get one from the US??? Quote Link to comment Share on other sites More sharing options...
woody Posted July 11, 2007 Report Share Posted July 11, 2007 Before you go mad with an air gun on the flywheel nut, they aren't all left hand thread. The MK1 has a smaller crank assembly and is a different thread from the MK2 onwards but off the top of my head I can't remember whether it's the MK1 or the later models that are left hand - later I think. Just make sure you know which you've got before letting rip with an air socket. It is possible to twist and break off the end (threaded part) of the crank if too much force is applied - yes, I've done it, although on the clutch side and manually, not with an air socket. A flywheel holder is pretty simple to make, long peice of 1" wide steel bar that will reach to the footrest with two lugs welded on it to fit in the holes in the flywheel, one about 12mm to fit in one of the the larger holes, one about 6mm to fit in the smaller hole that is a couple of inches away from one of the larger holes. Or make a V shape so you can use both of the larger holes either side of the nut. Either way, then just jam the other end of the bar above or below the footrest and it will hold the flywheel. You don't actually have to weld lugs on. I use a piece of bar with two holes drilled in it to take a 12mm and 6mm bolt and hold them in situ with gaffer tape. This holds them in place well enough to hold the flywheel - obviously better welded in place though. There is a tool to remove the cush drive sleeve and you can get one from Keith Lynas in the US - link to his site is on Mats Nyberg Ossa site. Don't know of anywhere to get one here. Or you can make one. I used a round piece of metal about 4mm thick and about 3" diameter. Drilled a hole in the centre wide enough to be a snug fit over the sleeve but it must be able to slide freely on the sleeve without being loose. Then machine a recess in the disc around the outside of the hole, 2mm deep and about the same in diameter. You then need two C shaped collets that will fit into the groove in the end of the sleeve but they must protrude from the sleeve rather than sit flush. I made these by finding a very thick washer that just happened to be the right outside diameter, thickness and inside diameter and cutting it in half. The idea is that you slide the disc onto the sleeve, fit the collets into the groove on the sleeve and then pull the disc towards the end of the sleeve so that the disc comes up against the collets, the collets fit snugly into the machined recess which stops the disc being removed from the sleeve, holds the disc in place and stops the collets dropping out. Then, using a conventional three legged puller around the back of the disc (which is why it needs to be about 3" in diameter, you can pull the sleeve off. These sleeves are a tapered fit and can be a real bitch to remove as they can be incredibly tight. If it is stubborn you can heat it and whilst it is under tension from the puller tap the end of the puller to try and shock it free. When they let go though, they can fly a good few feet. If the engines never been apart expect it to be really tight. Don't be tempted to try and get behind it and lever it off as you'll only damage the casing and and possibly break a piece off the sleeve - you won't lever it off, trust me. When you split the cases tap the shafts gently from the clutch side as you need all the gears to remain in the timing side casing when it splits rather than rolling all over the bench. If you can seperate it gently enough all the shims should stay on the shafts although they may also stick to the bearings in the clutch side casing so check that too. If you can keep them from falling out you can just reassemble it replacing the shims in their original positions - you are supposed to re-shim it but you should get away with doing that. There are shims on the crankshaft too, maybe both sides. Quote Link to comment Share on other sites More sharing options...
scotty Posted July 12, 2007 Author Report Share Posted July 12, 2007 Thanks for the reply Woody! i reckon ill send off for that special puller if its the right money! on a different note i think its time to get rid of my kt250 as its getting no use! cant say ive really got on with it! to me its always felt more of trail bike like a pukka trials bike! so its got to go! plus could do with making some space in the garage! Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 12, 2007 Report Share Posted July 12, 2007 Thanks for the reply Woody! i reckon ill send off for that special puller if its the right money! on a different note i think its time to get rid of my kt250 as its getting no use! cant say ive really got on with it! to me its always felt more of trail bike like a pukka trials bike! so its got to go! plus could do with making some space in the garage! I'd be surprised if the puller is more than $20. Well, for an Ossa, maybe $40. Quote Link to comment Share on other sites More sharing options...
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