Found the problem

Chrisj796 · Oct 9, 2020

Guy my in-law got bike from a few years back said they parked it when he was a kid after the transmission got stuck in third. Frame got “misplaced” at painters for 2 years and was found a few months back. In-law bought one already restored after he thought this one got stolen so he gave this to me. Got bike in boxes a few weeks back an started rebuilding the engine. After looking through gears everything looked great. Reassembled case an was going through gears by spinning the drum with my hands. Everything was looking good so I figured he must have been full of it. Put spindle an arm back together an tried to go through gears one more time. Shifted thru gears great but wouldn’t down shift. I found the problem lol.
Have no clue we’re busted piece is, must have fell out drain plug or something.

kirrbby · Oct 10, 2020

I don't see anything broke in your pics..? I see a missing shift star. You have that small primary gear on the trans shaft. It should go on the crank, and mesh with the clutch.

Chrisj796 · Oct 10, 2020

kirrbby said:
I don't see anything broke in your pics..? I see a missing shift star. You have that small primary gear on the trans shaft. It should go on the crank, and mesh with the clutch.

Tripod · Oct 10, 2020

Nice find. Will probably fire right up then with a good carb cleaning.

Chrisj796 · Oct 10, 2020

Tripod said:
Nice find. Will probably fire right up then with a good carb cleaning.

Ya engine looked great everything was in good shape but that, going to put a new top end on an move on the the next batch of boxes, got it for free so wife won’t mind if I put a few bucks in. Going to be a nice bike to ride with my k1.

69ST · Oct 10, 2020

Well that's first(!). The good news is that it's an easy repair, with the clutch & primary drive off the engine. Used shifter shaft assemblies are a dime a dozen. If you want NOS here you go.

Chrisj796 · Oct 10, 2020

racerx said:
Well that's first(!). The good news is that it's an easy repair, with the clutch & primary drive off the engine. Used shifter shaft assemblies are a dime a dozen. If you want NOS here you go.

Thanks I ordered one Thursday from NOSnow.
I can hear the gears slightly rubbing while spinning the main shaft or transmission shaft. One will spin the other with no resistance but if I hold one or the other they stop. Could this be a worn spacer somewhere in transmission?

69ST · Oct 10, 2020

Chrisj796 said:
Thanks I ordered one Thursday from NOSnow.
I can hear the gears slightly rubbing while spinning the main shaft or transmission shaft. One will spin the other with no resistance but if I hold one or the other they stop. Could this be a worn spacer somewhere in transmission?

Could be anything...or nothing. Need more info to comment intelligently on this. What I would suggest is "dry assembling" the lower end, once you have the replacement part, then bench-test...both static (which can be very misleading) and dynamically (which is a better indicator) , i.e. spinning the primary driven gear while attempting to shift through the gears.

These trannies don't usually like to bench-shift and testing with other than normal engine rotation, rpm and vertical orientation can reveal "problems" that don't actually exist. It takes healthy shift forks & pins to fully move the gears, then torque to lock them together while riding. Best advice I can offer, at present, verify every single thrust washer & c-clip using an exploded drawing and be sure that the shift forks, pins and gear themselves are all healthy.

Chrisj796 · Oct 10, 2020

racerx said:
Could be anything...or nothing. Need more info to comment intelligently on this. What I would suggest is "dry assembling" the lower end, once you have the replacement part, then bench-test...both static (which can be very misleading) and dynamically (which is a better indicator) , i.e. spinning the primary driven gear while attempting to shift through the gears.

These trannies don't usually like to bench-shift and testing with other than normal engine rotation, rpm and vertical orientation can reveal "problems" that don't actually exist. It takes healthy shift forks & pins to fully move the gears, then torque to lock them together while riding. Best advice I can offer, at present, verify every single thrust washer & c-clip using an exploded drawing and be sure that the shift forks, pins and gear themselves are all healthy.

Ok I will give that a shot, just seems like there are some gears not fully separating, figured something might be worn thin.

69ST · Oct 10, 2020

Chrisj796 said:
Ok I will give that a shot, just seems like there are some gears not fully separating, figured something might be worn thin.

I've seen a few gears with missing teeth, a few more with worn drive dogs & the pockets into which they seat. But gears that have been worn thin...never and it ain't gonna happen. That's not how they wear. They're made from incredibly hard alloy, that's why teeth can be broken (from extreme abuse) otherwise, something else (and very obvious) will fail long before that could happen. Only worn gear teeth I've seen were on ultra high mileage Honda 110 Nice motors, sourced used from Thailand...and those had at least 60K miles on them. FYI, the gear wear shows up as pitting on thrust sides of gear teeth, as the heat-treating depth is exceeded.

Now, that said, if the gears are not "separating" as you've described, the issue would be with either the shift linkage, shift forks/pins or in an extreme case the shift drum...or incorrect assembly. More likely, you're as yet unfamiliar with the mechanical operation of this trans...and understanding it fully isn't really necessary. FYI, not all of the gears slide laterally along the main or countershaft; some are stationary and remain tooth mesh at all times; their companion gears move, engaging & disengaging the drive dogs.

Best suggestion I have is to not overthink this. As long as the parts are in good condition and correctly assembled, the tranny will work properly and for more miles than it'll ever see.

Chrisj796 · Oct 10, 2020

racerx said:
I've seen a few gears with missing teeth, a few more with worn drive dogs & the pockets into which they seat. But gears that have been worn thin...never and it ain't gonna happen. That's not how they wear. They're made from incredibly hard alloy, that's why teeth can be broken (from extreme abuse) otherwise, something else (and very obvious) will fail long before that could happen. Only worn gear teeth I've seen were on ultra high mileage Honda 110 Nice motors, sourced used from Thailand...and those had at least 60K miles on them. FYI, the gear wear shows up as pitting on thrust sides of gear teeth, as the heat-treating depth is exceeded.

Now, that said, if the gears are not "separating" as you've described, the issue would be with either the shift linkage, shift forks/pins or in an extreme case the shift drum...or incorrect assembly. More likely, you're as yet unfamiliar with the mechanical operation of this trans...and understanding it fully isn't really necessary. FYI, not all of the gears slide laterally along the main or countershaft; some are stationary and remain tooth mesh at all times; their companion gears move, engaging & disengaging the drive dogs.

Best suggestion I have is to not overthink this. As long as the parts are in good condition and correctly assembled, the tranny will work properly and for more miles than it'll ever see.

I am going to leave it alone for now, have a buddy that’s going to take a look before I go any further. I’m thinking the slight clacking noise it’s just a symptom of being dry an gears touching slightly.

Found the problem

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