sbyrn Posted August 24, 2015 Report Share Posted August 24, 2015 Over the weekend the kick starter on my MAR shot craps and quit working. Pull the side cover off, kick start spring is intact and the shaft rotates freely. No metal in the oil. Just isn't making connection to turn the motor over. Thoughts? Can it be repaired without splitting the cases? Quote Link to comment Share on other sites More sharing options...
woody Posted August 24, 2015 Report Share Posted August 24, 2015 Although I know how the mechanism works, it's hard to imagine what's gone wrong, but from what you describe it sounds as though the ratchet isn't engaging to turn the gearbox mainshaft. I'm assuming that any part of the clutch isn't moving when you're rotating the kickstart. If not, it has to be inside the gearbox The ratchet is located onto the kickstart shaft on a spline, hard to imagine that's broken. The ratchet is forced along the shaft to engage with the kickstart gear as it has a cam, or ramp, on its outer edge which rides against a large headed screw that is screwed into the casing. As the shaft rotates, the 'ramp' rides along the screw head and forces the ratchet along the shaft to engage the gear. If the ratchet teeth aren't engaging with the gear teeth, either the ratchet isn't moving far enough (or at all - screw broken, fallen out?) or the ratchet teeth are broken. Only other thing I can think of that would stop the two meshing is that the large shim that sits between the clutch side crankcase and the kickstart gear is missing, which would allow the gear to sit too far to the left on the shaft and be out of reach of the ratchet as it is moved towards it. But if that was the case, you'd have been lucky to have ever started it. A possible test for that is to lay the bike on its right hand side which means the gear will slide towards the ratchet, then turn the kickstart slowly and see if it engages. Then repeat with the bike on its left side which would slide the gear away from the ratchet - if there is no shim (or the wrong shim?) If it doesn't engage then that's a possible cause Another possibility is that something on the gearbox mainshaft has broken but you don't say whether you could still use the bike - if you can, the mainshaft can't be broken Can't really think of anything else but from what you're describing, it's going to be internal so will need to be split. If you split it be careful to do it gently as there are shims everywhere on various shafts and selector drum and you need them to go back where they came from when reassembling. If they're all over the bench with the rest of the gearbox when the cases split you won't know where they came from. And they can stick to either the bearings or the ends of gears so you have to look hard. 3 Quote Link to comment Share on other sites More sharing options...
sbyrn Posted August 24, 2015 Author Report Share Posted August 24, 2015 Woody, havent split the cases but I suspect it is as you describe. Pulling the plug, you can roll the bike in gear and it shifts smoothly. Can't imagine why it just stopped working. It was running fine, shut it off to walk a section and no go when I went to kick it. Basically no resistance at all moving the kick starter through it's arc. Definitely sounds like the cases will need to be split. Need to think on that bit as it appears to be above my ablities. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
twinshock giles Posted August 24, 2015 Report Share Posted August 24, 2015 Could it be a broken kickstart shaft? I've never seen or heard of it happening on an Ossa but I can't think what else it could be. The only thing I have had close to it was a 350 which only started to engage after about 2/3rds of a rotation of the kickstart shaft. I think that was down to mis matched parts and needing reshiming though, it didn't just suddenly happen. Quote Link to comment Share on other sites More sharing options...
goudrons Posted August 25, 2015 Report Share Posted August 25, 2015 The kick starter gear obviously spins freely on the starter shaft when not in use, but when you start to move the lever back, it engages small, castilated teeth connected to the shaft with small castilated teeth in the centre of the gear. It could be one or both sets of castilated teeth have stripped or worn down smooth. You can clearly see the teeth here. The smaller part is splined to the starter shaft and the gear spins on the same shaft, pull it up (the smaller part slides up the splines on the inner end of the shaft) and the castilated teeth (should) lock up. http://www.ebay.co.uk/itm/KICK-START-SHAFT-GEARS-1973-OSSA-MAR-MICK-ANDREWS-REPLICA-250-TRIALS-72-73-74-/171554449626#ht_839wt_1161 2 Quote Link to comment Share on other sites More sharing options...
sbyrn Posted August 25, 2015 Author Report Share Posted August 25, 2015 Gourdons, Thanks, I suspected it worked in that fashion some way or other. Now to decide what to do. Splitting the cases to replace these is above my ability. Not to many Ossa mechanics left in the US. I'd hate to just let the old girl sit or part her out. Quote Link to comment Share on other sites More sharing options...
sbyrn Posted August 25, 2015 Author Report Share Posted August 25, 2015 Gourdons, Thanks, I suspected it worked in that fashion some way or other. Now to decide what to do. Splitting the cases to replace these is above my ability. Not to many Ossa mechanics left in the US. I'd hate to just let the old girl sit or part her out. If I did decide to try and fix it, are there any special Ossa tools I need or may it be done with normal tools? Quote Link to comment Share on other sites More sharing options...
twinshock giles Posted August 25, 2015 Report Share Posted August 25, 2015 You don't need an Ossa specialist - anybody who is used to working on 2 strokes should be able to split it and rebuild it for you, probably your best bet would be to find someone who rebuilds MX engines. The Ossa engine is about as simple as it gets to work on and split, the only tricky thing to remember is that there are shims everywhere and you really don't want to mix them up when you take it apart. I think the only special tools you are likely to need is a clutch holder so you an undo the centre nut (or just use an impact wrench) and flywheel (magneto) puller. An impact driver is usefull to loosen the screws that hold the casings together. Other than that there may be a special tool for holding/ dismantling the cush drive on the end of the crank but i've never had one. While it is apart you may as well fit new bearings and seals they are only a few extra £/$ Quote Link to comment Share on other sites More sharing options...
goudrons Posted August 26, 2015 Report Share Posted August 26, 2015 (edited) As written, you also need a tool to remove the primary side's "Cush Drive". The primary sprocket isn't a direct fit to the crank, there's a funny sleeve/spring arrangement on the left hand crank known as the Cust Drive and it needs drawing off the taper. You'll never split the cases otherwise and I wouldn't recommend the hammer for this! http://www.ossaplanet.com/partspage.html I believe there are a few in the US that can help you, like above. Edited August 26, 2015 by goudrons Quote Link to comment Share on other sites More sharing options...
sbyrn Posted August 26, 2015 Author Report Share Posted August 26, 2015 Thanks Goudrons. She may have to sit a while. Quote Link to comment Share on other sites More sharing options...
scot taco Posted August 29, 2015 Report Share Posted August 29, 2015 I sent you a PM sbyrn. 1 Quote Link to comment Share on other sites More sharing options...
old trials fanatic Posted August 29, 2015 Report Share Posted August 29, 2015 Ive got a really nice 350 Ossa motor from a TR77 im selling. Never been trialed. Problem is its in the UK and carriage would be quite a bit but its here if youre interested Quote Link to comment Share on other sites More sharing options...
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