Sheesouthafrica

Been reading this form for the past month or so. I live way out in South Africa and recently (just short of a year ago) got myself a Banshee. The Bike is reasonably standard, FMF Pipes, silences, Wheel spacers etc. Just the basics. I am hoping someone here will be able to help me with some technical info. Let me give you the basic run down of what happened: I was riding in the dunes and the bike got stuck in 2nd and 3rd, I could not select any of the other gears. I was on my way back to the car when I could suddenly select 4th, and all the other gears for that matter. So I kept riding, but every now and again the bike jumped from what I think was 4th or somewhere thereabouts into neutral. Perhaps I was being a bit oversensitive but I’m convinced I could hear a high pitched whining noise from the box. I was so befuck when I got home I left it for a few weeks in my garage and did nothing. The weekend past I started working on the bike, pulled the covers off to have a look what going on inside. When I removed the clutch cover I found a small twisted piece of metal laying in the bottom, doesn’t look much like a bearing that has failed or anything serious but I don’t know. My concern at the moment if I’m looking at the gearbox from the clutch side, to my right is the crank shaft. In the centre is what I would call the input shaft and to the left is the output shaft. With a gear selected and I turn the “input shaft” I can turn it ¾ turn before the “output shaft” starts to turn. That appears to be a bit excessive with regard to free-play. The casing is not split and I’m hoping to not have to pull the motor, but at this point it looks like I’m going to have to. Is that amount of free-play normal? The previous owner of the bike (who happens to be my boss) loaned to bike out and it then also got stuck in 2nd gear and the rider jumped on the gear leaver to get it into 1st this obviously did not work and apparently in the process managed to break something on the side cover and burn out the clutch. This was all repaired by a bike shop, shortly after he got the bike back I bought it. We ride almost every Saturday and ride hard! (who doesn’t ride a Shee hard) We do allot of tight turns with hard accelerating, so the bike spends almost all of its time in 1st and 2nd. I had been riding for about 4 months and the bike started jumping out of 2nd into neutral, I decided to change the gear oil and did a bit of research on the net and the general recommendation was ATF. Having loads of it at home I decided to use it. The first ride with ATF was awesome! no more jumping out of gear, smooth gear changes. For the first 2 hours or so. Knowing the oil would need to be changed more frequently I figured perhaps the ATF was contaminated with the old oil that came out (which was EPX90) and I changed it again. Which I did and my next ride the same thing happened, jumping out of second about 2 hours in. Drained out the ATF and it was all discoloured as if the oil had broken down, I knew it would need to be changed more regularly but this is a bit excessive. I kept changing the oil before every ride until my stash of ATF ran out. Then back to my dear fried Mr Google, and did allot more research about gearbox oils. I found out the original oil is a 75W-90 grade, and we use Castrol Syntrax 75W-90 at work. I decided to take a chance and use it, worst case it would bugger up my clutch plates. The bike drove fine with the 75W-90 for months! Until the above happened. Apologies for the long post, but wanted to give ALL the details giving you as much info as possible. My main concern is I want to know how much free-play is acceptable in the gearbox. Many, many thanks in advance.