I completely thunked it the first time I read it. This thread is quality use of the interwebs. Congrats on a classic.
Nice job. I bought a second hand 'mystery' engine on Ebay. I decided to completely strip it down so I could paint all the cases separately. Well, after spending a lot of time and money, I rebuilt it I find that it won't change gear properly. I've had the cases apart four times. Everything looks straight and fine. It just won't go into neutral while on my bench, spinning the shafts by hand. No matter how I turn the shift drum, there is no point where the main and counter shaft are not driving each other. I've checked the gearbox to my manual endlessly. It's correct. Any ideas ??
<center> Gearbox Operation. </center> <hr> Posted by JAW - while the XR was in pieces JAW grabs the camera and takes some happy snaps in order to share some understanding of how a motorbike gearbox works. <table summary="table" border="0"> <caption> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> Power enters from the clutch onto the countershaft and leaves via one of the gear ratios out the sproket. "X" means this cog idles; ie is able to free spin. Cogs are numbered.</center> </td> <td valign="top"> Power Flow. Mumbo from the engine hits the gearbox via the clutch and spins the countershaft. You can see there are 5 cogs on the countershaft and these correspond to cogs on the mainshaft, each of the cog pairs produces a different ratio. This box is... yeah okay, you guessed it, a 5 speed The "X" crosses mean the cog can free spin. At the moment in fact, the gearbox is in neutral. You'll notice for every cog that can free spin it's mate cannot - it is locked to the shaft. It can move backwards and forwards, but it always spins with the shaft it is attached to. </td> </tr> </tbody> </table> <table summary="table" border="0"> <caption> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> Selection. From the first photo you can see firstly how a cog is locked to it's shaft but can move from side to side - it is splined. Are ya with me? A shows the lumps on the shaft and B shows the inverted lumps in the cog. C which we shall call a "locker" for want of a better term performs the selection of a gear. This mechanism is shown better in the next photo... </td> <td valign="top"> <center> A cog with it's (B) spline connection and (C) "lockers".</center> </td> </tr> </tbody> </table> <table summary="table" border="0"> <caption> </caption><tbody> </tbody> <tbody> <tr> <td valign="top">Lumps and holes... when a gear that is locked to the shaft gets told to "swing left" or "swing right" as the case may be, the locker mates with it's next door neighbour cog. By an amazing coincidence, that cog is normally and idler, but once joined it too is locked to the shaft and therefore must spin with the shaft. This how gears are selected - the rider essentially starts moving the cog across to it's next door neighbour. When the locker lines up with the corresponding hole, in she clunks. </td> <td valign="top"> <center> A cog and it's neighbour - with (B) spline connection and (C) "lockers".</center> </td> </tr> </tbody> </table> Choose a Ratio. First lets just consider neutral again. When in neutral, no cogs are locked together, so all gear ratios have one cog that is free spinning, and one cog that is locked to the shaft. What happens? Nothing! Power is fed via the clutch to the countershaft and can't do anything! (Note - the first picture on this page shows the gearbox in neutral). <table summary="table" border="0"> <caption> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> First gear is selected.</center> </td> <td valign="top">But now when you select 1st gear, the bottom neighbour has slid to the right. Look carefully at the picture, it's the lower cog on the 4th gear that has moved right and locked. Okay the top cog was already locked to the shaft, and thanks to lower 4th gear the bottom is too. Nothing has happened to 4th gear, the top of 4th is still free-spinning. All the other cogs remain the same too. The 1st gear top cog has 12 teeth, the bottom cog has 28. So now when power enters the countershaft 1st gear is selected and for every one revolution, the mainshaft does 12/28 = 0.43 revolutions. Yah, we're moving! </td> </tr> </tbody> </table> Examine the next 4 photos, each one represents a gear selection. In each case one of the selection cogs - ie those ones that don't free spin - has moved across to lock up with it's neighbour. Note the when you change between gears the previously locked gear must first disengage before the new one can engage. Think about what would happen if two gears were selected at the same time... Ugly. <center> <table summary="table" border="0"> <caption> <center></center> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> Second gear is selected.</center> </td> <td valign="top"> <center> Third gear is selected.</center> </td> </tr> </tbody> </table> </center> <center> <table summary="table" border="0"> <caption> <center></center> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> Fourth gear is selected.</center> </td> <td valign="top"> <center> Fifth gear is selected.</center> </td> </tr> </tbody> </table> </center> <table summary="table" border="0"> <caption> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> The selector forks in place.</center> </td> <td valign="top"> Selector forks. Well this is all well and good JAW, but how does my left foot make it happen? Look at this picture, what you can see are the selector forks. They slot in on the selector cogs and push them left and right, right? Those little stumps on the top of the selector forks, at the very top are controlled by a programmed lump of metal known as the shift drum. Heh, there is a mechanical program running in your bike. Let's not refer to it as software though shall we... </td> </tr> </tbody> </table> <table summary="table" border="0"> <caption> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> Shift drum. And this is it. The deeper worm holes are where those little stumps fit in. By rotating the shift drum clockwise or counter clockwise it will push the selector forks left or right, depending on what the drum is "programmed" with. Lets bring it all together... </td> <td valign="top"> <center> The brains of the situation - the shift drum.</center> </td> </tr> </tbody> </table> <center> <table summary="table" border="0"> <caption> <center></center> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> How the shift drum fits together.</center> </td> <td valign="top"> <center> From a different angle - you can see on the end of the shift drum the "stopper plate".</center> </td> </tr> </tbody> </table> </center> From the foot... The final part of the picture is the rotation of the shift drum. On one end of the shift drum, the end with the bolt hangin out, is the stopped plate. It has a "clicker" wheel (the shift pawl) that holds the drum in position when a gear is selected. On the other end is the selector rod itself, with a little claw that basically connected to your foot. When you push down on the gear lever the little claw pushes the shift drum one stopper click clockwise, and vice versa. So now that you've seen it, and how "clunky" it can be, you are gonna be nice to your gearbox and at least use the clutch in 1st and 2nd gear aren't you? <center> <table summary="table" border="0"> <caption> <center></center> </caption><tbody> </tbody> <tbody> <tr> <td valign="top"> <center> The stopper plate arrangement.</center> </td> <td valign="top"> <center> The selector spindle with "claw" (far right out of picture is the drum). That shaft you see it the gear selector lever shaft itself. Notice here too the broken part and thus why I had the gearbox out in the first place...</center> </td> </tr> </tbody> </table> </center> <hr> <table summary="table" border="0" width="360"><caption> </caption></table>
It all looks good... I assume, once the gearbox and forks are in correctly. The drum can only go in one way can't it ?? It has to be in rotation to match the pins on the selector forks. I can get the gearbox into first gear but the drum doesn't seem to match up. Hmmmm. Maybe I'm just being retarded. It is below freezing here hahah I have four other engines the same with good boxes. I'll pull one apart and compare. Worst thing about second hand engines. You don't know if they're f**ked before you start working on them.
Ted Magnum- While spinning the motor you need a third hand to put some tension on the countershaft or it will just keep spinning like it is in gear. At least mine did. Sometimes it is the simple stuff.
Steve, can you identify those six bearings? Also, where did you get the nice looking oil lines in this?
Correct me if I'm wrong..... The steel shaft that the centre selector is bolted to needs to move up and down freely when the drum shifts. It HAS TO as the 'centre' selector is bolted to it. Mine doesn't. Even though it seems to be straight. I removed the selectors and separately, they all slide up and down it freely. I made a little video. https://www.youtube.com/watch?v=CbUPTldq6qU
Your video shows private and doesn't work. Yes the shaft needs to move. Remove the side shift forks and using just the center fork try to see if you can get it to move. I have never had a problem like yours.
Try again.... https://www.youtube.com/watch?v=CbUPTldq6qU I've measured everything I can. All in spec. I've rebuilt COUNTLESS engines of all types and never had a problem like this. It's so weird. It was an Ebay engine. I don't know if it was like this before I spilt the cases. I'll never break an engine without checking the gearbox function again
Is that as far as you have assembled the engine? Leaving the right case half off? If so do install the right case half and the star piece that bolts to the end of the shift drum and the spring and roller arm. THEN try to shift the transmission What your doing is simply trying to get the center shift fork to move but the gear it's attached to is bound up by the one one's on top of it plus your not rotating the main shaft to get everything spimming.
This is my problem in Videos.... With the drum removed. (lock pin installed), the shaft will slide freely. https://www.youtube.com/watch?v=j2kyKjngReQ With the drum installed but the locking pin REMOVED. It also seems to function correctly. https://www.youtube.com/watch?v=vTBm76wV2dU The problem is when the pin installed. This pulls everything together. Then it jams up. https://www.youtube.com/watch?v=ljr5UgHD3_I This would suggest something is out of line. It could be the selector fork shaft. Even though I've NEVER heard of one bending before. Perhaps and more likely it's the centre selector fork. Which would also perhaps explain why it wouldn't 'unmesh' when neutral was selected on the drum. Everything looks nice and straight. I can't really measure the forks for straightness as they all have a natural curve in them. Anyway. I'm open to all suggestions here. Thanks.
Had it all together a few times now. I originally found the problem AFTER Id put it back together. (I split the engine to paint it). With it all assembled, I was struggling to get the drum into neutral. It was jamming up. And when the drum did show neutral, the gear shafts were still locked together. The gear it's trying to move is not held up. They're positioned to accept the dogs easily. But I see what you mean. I've spilt the gears apart and compared all parts with the fiches and manuals I have. Everything is correct. There is NO wear on any gears or selector dogs. I've been a motorcycle technician for ten years. Many years with main dealers. When I've had problems like this, I've just swapped the whole mechanism on warranties for customers. That's not an option for me. I have to do this on ECONOMY. Honda parts are DAM expensive. Especially here in the U.K where they cost double. Just one of those selector forks costs £100 here ($150 USD). However, this is the first XR650L I've had the cases apart on. It's pretty simple in there.... :/
Thanks... I've just bought a drum, full set of forks and the shaft on Ebay in the U.K. Off an NX650 (Same engine). Only £25. 'Assuming' they're all straight, it will help me diagnose the problem. But nice to know you're packing forks if required.
Are the bearings something I can swap out myself or should I have the machinist do it when I take the cylinder in to be bored out?
Which bearings? You can do all but the left crank bearing that seems to stay on the crank. Call me later.