Some time back I pulled the transmission of my 1971 TR6R apart to replace the main shaft seal and diagnose some shifting problems. The seal had deteriorated and was leaking oil when the bike was on the side stand so I needed to address that. Also, shifting had gotten dodgy...I figured that out along the way and squared it up too.
When I searched online for advice on condition, reassembly, etc., I was not really able to find what I needed. So, when I completed the project, I decided to post a couple of pointers in the hope that the next guy will find the process easier.
First, any service manual from any year that shows you the four speed gear assembly (main shaft, lay shaft, gears, shift forks) will show you a good photo of how to physically handle the gears. The difference between '70 and '71 is the "plunger" versus "leaf spring".
This is not the big deal that many people make it out to be. Either works perfectly well and bashing the OIF leaf spring over this is gratuitous. I have one of both, they both shift the same. Anyway, what matters is that the 1971 Service Manual is hard to find yet it gives the correct guidance on assembly. I've excerpted a couple images and offer some suggestions to make it easier to do.
In any service manual from this era, read the description carefully and you'll learn that the two shift forks have a slightly different radius. The manual tells you which goes in which position. There are numbers stamped on the forks, too, that help keep them in their proper place. AND, you can mark them with a Sharpie when you pull the gear set out. This little tidbit is important.
If the bike has any appreciable mileage, you might as well replace the shifting leaf spring assembly. They're inexpensive. Order one along with the seal or whatever else you're doing. Clean out the box nicely. No need for kerosene, etc., just wipe it out. Follow the manual's instructions on removing the main shaft seal, if that is what you're doing, or replace busted gears or whatever.
OK, now the fun. The difference between 1970 and earlier and 1971 and later is obvious. Offering the gear pack back into the case is the same for both EXCEPT for the position of the CAM PLATE when you start and the position of the cam plate shift "quadrant". See the first photo for reference. This is the correct cam plate position for 1971.
In this second photo note the THRUST WASHER as well. Many times, if you offer the gear cluster to the box and assemble the case doing everything right, the gears will still bind up. This is because the thrust washer has slipped out of position. It is a locating hole that orients it correctly. A little lithium grease on the back of the washer when you put it in there will help keep it in correctly. Then be careful sliding the gear set into position and once it is in there, look inside carefully with a flashlight and if you see the washer had slipped, do it over. It sounds worse than it is...take your time, be gentle, all will be well.
Next, you need to line up inner transmission cover. In the third photo, note the dotted line that is on the same plane as the center of the main shaft. Now look at the photo of my gearbox and note the black Sharpie line and where it is. This is the correct position. When you offer the case, follow the manual instructions but note that you'll have rotated the cam plate slightly counterclockwise inside the transmission case so that when the unique 1971 shift spring/lever doodad enters the case it will contact the cam plate and rotate it clockwise slightly putting the transmission into FOURTH GEAR. The photos I've posted show you exactly how the QUADRANT teeth and cam plate must be aligned to do this. Follow this method and it'll work perfectly.
Here is a photo of my transmission with a Sharpie mark that shows the correct alignment when you offer the inner case to the main case.
There you go...all it takes now is patience. I'd mention also not to set the gasket in place or goop it up until you've "test fit" and know what to expect. But trust me, ALL of these bikes offering the whole gear set into the case is tedious. The OIF type are no more so, just different. And know that it will shift just fine for thousands and thousands of miles and when/if it comes time to replace the leaf spring, you need NOT take gears out and all that jazz, just fit a new leaf assembly to the inner case, put the cam plate in the correct position (as in the 1971 manual photo), rotate slightly to allow the leaf to push the cam plate into fourth when you install the case, and put the inner case back on. That whole process will go fast with these photos. Enjoy your OIF - they're great machines.
When I searched online for advice on condition, reassembly, etc., I was not really able to find what I needed. So, when I completed the project, I decided to post a couple of pointers in the hope that the next guy will find the process easier.
First, any service manual from any year that shows you the four speed gear assembly (main shaft, lay shaft, gears, shift forks) will show you a good photo of how to physically handle the gears. The difference between '70 and '71 is the "plunger" versus "leaf spring".
This is not the big deal that many people make it out to be. Either works perfectly well and bashing the OIF leaf spring over this is gratuitous. I have one of both, they both shift the same. Anyway, what matters is that the 1971 Service Manual is hard to find yet it gives the correct guidance on assembly. I've excerpted a couple images and offer some suggestions to make it easier to do.
In any service manual from this era, read the description carefully and you'll learn that the two shift forks have a slightly different radius. The manual tells you which goes in which position. There are numbers stamped on the forks, too, that help keep them in their proper place. AND, you can mark them with a Sharpie when you pull the gear set out. This little tidbit is important.
If the bike has any appreciable mileage, you might as well replace the shifting leaf spring assembly. They're inexpensive. Order one along with the seal or whatever else you're doing. Clean out the box nicely. No need for kerosene, etc., just wipe it out. Follow the manual's instructions on removing the main shaft seal, if that is what you're doing, or replace busted gears or whatever.
OK, now the fun. The difference between 1970 and earlier and 1971 and later is obvious. Offering the gear pack back into the case is the same for both EXCEPT for the position of the CAM PLATE when you start and the position of the cam plate shift "quadrant". See the first photo for reference. This is the correct cam plate position for 1971.
In this second photo note the THRUST WASHER as well. Many times, if you offer the gear cluster to the box and assemble the case doing everything right, the gears will still bind up. This is because the thrust washer has slipped out of position. It is a locating hole that orients it correctly. A little lithium grease on the back of the washer when you put it in there will help keep it in correctly. Then be careful sliding the gear set into position and once it is in there, look inside carefully with a flashlight and if you see the washer had slipped, do it over. It sounds worse than it is...take your time, be gentle, all will be well.
Next, you need to line up inner transmission cover. In the third photo, note the dotted line that is on the same plane as the center of the main shaft. Now look at the photo of my gearbox and note the black Sharpie line and where it is. This is the correct position. When you offer the case, follow the manual instructions but note that you'll have rotated the cam plate slightly counterclockwise inside the transmission case so that when the unique 1971 shift spring/lever doodad enters the case it will contact the cam plate and rotate it clockwise slightly putting the transmission into FOURTH GEAR. The photos I've posted show you exactly how the QUADRANT teeth and cam plate must be aligned to do this. Follow this method and it'll work perfectly.
Here is a photo of my transmission with a Sharpie mark that shows the correct alignment when you offer the inner case to the main case.
There you go...all it takes now is patience. I'd mention also not to set the gasket in place or goop it up until you've "test fit" and know what to expect. But trust me, ALL of these bikes offering the whole gear set into the case is tedious. The OIF type are no more so, just different. And know that it will shift just fine for thousands and thousands of miles and when/if it comes time to replace the leaf spring, you need NOT take gears out and all that jazz, just fit a new leaf assembly to the inner case, put the cam plate in the correct position (as in the 1971 manual photo), rotate slightly to allow the leaf to push the cam plate into fourth when you install the case, and put the inner case back on. That whole process will go fast with these photos. Enjoy your OIF - they're great machines.
