MOTOBRICK.COM
TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: ronin47 on April 18, 2020, 12:58:26 PM
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Gear Shifting problem, selector drum, gear shifting fork, output shaft measures
Lots of valuable info I found in this forum to be able to tear down the bike. Many thanks for all posts, that is just fantastic.
Maybe someone can help with my below problem, couldn’t find any answers in the forum.
I have bought my friends bike knowing there was a gear shifting problem.
He was using industrial boots to be able to shift the gear from 2nd to 3rd , (when I tried with normal shoes it was impossible for me). He decided to sell and I decided buy and repair. During teardown, I saw oil leaks all around the body. Bike is @ 70K km, seems gearbox opened before, I saw screwdriver force signs. Splines are in good condition.
I have 3 suspects however I couldn’t relate it with a problem and I don’t know how to solve. My suspects are selector drum, Gear Shifting Fork 1st & 2nd gear and output shaft. (I am not an expert or engineer, these are my best guesses)
1/ Selector drum has wears, seems many of them normal (based on forum feedbacks), except one of them.
Gear Shifting Fork 1st & 2nd, made a cavity at lowest point of it’s valley at the upper side (see picture)
I took of the Gear shifting fork 1st & 2nd, I realized that small aluminum roller of gear shifting fork was not in place. I found it in the gearbox. I have controlled the pictures I took while opening the gearbox, before I removed the GSF, it was already on the floor of gearbox. Maybe during the opening it fell. If it was not like that, I don’t know if gear shifting could work without, and if it could work, can cavity be the result of this?
2/ Gear Shifting Fork 1st & 2nd has a wear at the down side, (see pictures).
I have ordered used GSF, I will replace it. In order to avoid re-occurrence of the problem I decided to check further.
3/ In order to find out the reason of Gear Shifting Fork wear, I have checked selector fork shafts, no bending. I don’t know if Gear Shifting Fork 1st & 2nd has a bending, seemed to me normal but there can be a bending. Thinking that if all parts in place with correct measure searched and I found out assembling measurements of output shaft. I have measured Longitudinal dimensions as shown, I have measured 125 mm which should be 125,8 mm -0,1.
I kindly would like to ask your opinions about;
1/ Is this selector drum still usable? taking into consideration possibility of working without roller until now.
I have tried without oil and disconnecting the GSForks, it is shifting, I don’t know with a force if it can still work.
2/what could cause a wear of Gear Shifting Fork 1st & 2nd, problem is shifting from second gear to third gear. Not shifting from 1st to 2nd .
3/ Longitudinal dimension has a difference of 0,8 mm, it is out of specs, can that cause a problem?, if yes I need to adjust shim thicknesses, which shim(s) to be replaced, how can I find current shim’s thicknesses? Gap is 0,8 mm, shims are between 1.6-2mm, I assume if I need to change I have to change more than 1 shim. Or any other solution?
(http://www.motobrick.com/gallery/3/6728-180420124307.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124343-3030330.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124352-30371207.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124351-30361251.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124348-30342205.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124354-30392278.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124347-30341608.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124356-3041363.jpeg)
(http://www.motobrick.com/gallery/3/6728-180420124345-30321632.jpeg)
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Are you familiar with the term, “stacking?” I use it with gunsmithing and mechanics. It’s when so many little things are out of spec, they (as a whole) cause the mechanism to function improperly, or, not function at all. Then, in other cases, there are so many larger issues (not major or detrimental), that one (in and of itself) can cause improper function or failure. Based on what you’ve described and pictured, you have a host of some seriously large issues.
I’m going to preface this with… Save yourself the aggravation and find a low-mileage gearbox and install that one. If you choose to rebuild it, make sure you rebuild it to the letter of the manual. You will have yourself so much frustration and heartache.
You mentioned oil around the body. Is that the whole motorcycle, around the engine, around the gearbox…?
Great to hear the splines are in good shape. Protect them during the rebuild. Not absolutely necessary, but it’s worth it.
When I fixed mine, I couldn’t get it to down-shift, and it ended up being the shifting roll. My video https://www.youtube.com/watch?v=gWexDgK0lQ4 .
To answer your questions, honestly, I would not use the shifting roll. Find one in better condition and use that. Again, you are going to do a lot of work in vain if you don’t reduce your stacking issues. Obviously, this is just my opinion. Be patient and do it right.
As far as what may cause the wear? How steady is the steel step plate on top of the shifting roll? If it isn’t solid, that can be the beginning of the issues; that’s what did me in.
How about the screw (23311451091) that goes into the selector shaft? Was it tight?
Shims can definitely be an issue, but they’d stack to the problem. If in doubt, measure and (again) do it right.
I have some parts if you need them, but my roll and step plate are shot.
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greetings...
has this s been delooped... posst up some photos of this s before you commenced to tear down the bike..
j o
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I'll echo Jay's comment: "Save yourself the aggravation and find a low-mileage gearbox and install that one." Especially if it shows evidence that someone else has been into it. If they left obvious tool marks on it getting into it, makes one wonder/concerned how careful they were once inside..... :johnny
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A gearbox from a running bike will cost less than the parts you will probably end up purchasing to repair what you have. Not to mention all the chances that you will have to mess something up in there.
As Scott mentioned, who knows what the previous mechanic might have done?
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Thank you for your support ! replacing the gearbox seems the best solution since I crashed to an iceberg.
In the meantime, it is a good learning and I will try to repair and share my experiences here.
By shifting, selector drum is giving a movement of 4mm to the fork, like Jay mentioned, this 4mm movement triggers all shifting process, all mechanism should be in exact specs, no tolerance allowed.
If a gear shifting fork is not engaging with a gear wheel with (+-1) 90 degrees angle, it creates a friction with spline, which makes the movement almost impossible.
Like in my case, 2nd gear jams and not allowing 3rd gear's movement, if you force more it can move but it damages your selector drum's line/valley.
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Are you familiar with the term, “stacking?” I use it with gunsmithing and mechanics. It’s when so many little things are out of spec, they (as a whole) cause the mechanism to function improperly, or, not function at all. Then, in other cases, there are so many larger issues (not major or detrimental), that one (in and of itself) can cause improper function or failure. Based on what you’ve described and pictured, you have a host of some seriously large issues.
I’m going to preface this with… Save yourself the aggravation and find a low-mileage gearbox and install that one. If you choose to rebuild it, make sure you rebuild it to the letter of the manual. You will have yourself so much frustration and heartache.
You mentioned oil around the body. Is that the whole motorcycle, around the engine, around the gearbox…?
Great to hear the splines are in good shape. Protect them during the rebuild. Not absolutely necessary, but it’s worth it.
When I fixed mine, I couldn’t get it to down-shift, and it ended up being the shifting roll. My video https://www.youtube.com/watch?v=gWexDgK0lQ4 .
To answer your questions, honestly, I would not use the shifting roll. Find one in better condition and use that. Again, you are going to do a lot of work in vain if you don’t reduce your stacking issues. Obviously, this is just my opinion. Be patient and do it right.
As far as what may cause the wear? How steady is the steel step plate on top of the shifting roll? If it isn’t solid, that can be the beginning of the issues; that’s what did me in.
How about the screw (23311451091) that goes into the selector shaft? Was it tight?
Shims can definitely be an issue, but they’d stack to the problem. If in doubt, measure and (again) do it right.
I have some parts if you need them, but my roll and step plate are shot.
Thanks for all valuable feedback, I have checked screw (23311451091) (5mm hex fits), it is quite tight.
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greetings...
has this s been delooped... posst up some photos of this s before you commenced to tear down the bike..
j o
Hi Johnny, here they are, that beauty not properly maintained by the old owners.
(http://www.motobrick.com/gallery/3/6728-190420093724-30581366.jpeg)
(http://www.motobrick.com/gallery/3/6728-190420093724-30582072.jpeg)
(http://www.motobrick.com/gallery/3/6728-190420093731-30601269.jpeg)
(http://www.motobrick.com/gallery/3/6728-190420093729-3060668.jpeg)
(http://www.motobrick.com/gallery/3/6728-190420093645-3042466.jpeg)
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(http://www.motobrick.com/gallery/3/6728-190420093653-3047655.jpeg)
(http://www.motobrick.com/gallery/3/6728-190420093657-30481951.jpeg)