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Discussion Starter · #1 ·
I had the bike out at VIR the last couple days and was having issues shifting from 4th to 3rd. I had the issue once or twice last week at NCbike but i had attributed it mostly to new boots and just me being rusty.

Going into heavy breaking zones i would try to go from 5th or 6th to 3rd and it would usually go into 4th fine, but I would try clutching and shifting multiple times before it would actually shift. It got to the point that I would roll wide through the corner wide in a high gear and then would have shift down once the bike seemed to settle down. Through the pit it would go up and down gears with no issue. No problem going up gears and no point did it pop out of gear.

I adjusted clutch cable a few times, adjusted shift linkage to make sure all my angles were as good as possible and no binding in the rearsets. changed the oil back to Motul from Amsoil just to see if it helped. It seemed to run better the first couple laps while the transmission was cool but came back on the third or so lap.

I'm thinking shift fork?
 

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Discussion Starter · #3 ·
Ya know, now that you mention it, i don't recall if it may have been stuck in position. It's certainly a possibility which might also explain why after i accelerated with it in a higher gear a bit i could shift with no problem. that's a lot easier initial inspection compared to rebuilding a transmission with only 8k miles. I also changed the oil between day one and two and had no evidence of metal particles.
 

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Discussion Starter · #4 ·
What ended up being your issue? A clutch removal I can probably handle. A full trans rebuild is way above me.

Maybe @MacBandit will stop by to chime in. Would love to hear a bit more from him about the shift star.

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I used to occasionally get false neutrals on downshifts.... rolling through corners with no engine braking or throttle ain't much fun. A Sato shift spindle holder fixed it up. The issue is that the shift spindle sticks out unsupported pretty far from the transmission, and can bind a bit.

https://satoracing.com/rearsets675.htm#shiftspindleholder

Edit: Just noticed that cjc also mentioned the Sato unit.
 

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Discussion Starter · #7 ·
I'm thinking i will attempt to tackle this level of work myself. I should have a friend available to help that has a lot more experience than I in this department. I have the full service manual, but i'm sure with the yoyodyne the process will be slightly different, but not by much.

Here's what i'm looking at ordering, probable more than i need, but I rather have extra:
clutch holding tool
detent arm
detent arm spring
detent wheel
gear change mechanism and arm
Sato gear change mechanism support
Clutch nut (replacement item according to manual)
clutch C washer (replacement item according to manual)

anything else? should i consider doing stiffer clutch springs? I've heard no real complaints on the factory stiffness and they work well with the slipper.
 

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Discussion Starter · #11 ·
Not that you need me to validate but I think you're on the right track. It's most likely a shift selector spring, worn selector fork, or weak detent wheel spring.
I guess the hope at this point is not the fork because then it's a split case and missing a couple months of the track season.

Have you done a yoyodyne before? Much different than the manual shows for a factory clutch?

Everyone's help is very much appreciated. I'm going to start ordering parts tomorrow (ordered the Sato spindle support tonight).

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Not that you need me to validate but I think you're on the right track. It's most likely a shift selector spring, worn selector fork, or weak detent wheel spring.
I guess the hope at this point is not the fork because then it's a split case and missing a couple months of the track season.

Have you done a yoyodyne before? Much different than the manual shows for a factory clutch?

Everyone's help is very much appreciated. I'm going to start ordering parts tomorrow (ordered the Sato spindle support tonight).

Sent from my SM-G965U using Tapatalk
I have. The instructions that come with it are really good, I had no issues. I'd call myself basically competent with mechanical stuff, but far from any kind of expert.
 

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I guess the hope at this point is not the fork because then it's a split case and missing a couple months of the track season.

Have you done a yoyodyne before? Much different than the manual shows for a factory clutch?

Everyone's help is very much appreciated. I'm going to start ordering parts tomorrow (ordered the Sato spindle support tonight).

Sent from my SM-G965U using Tapatalk
The only way it's a shift fork is if you crashed hard enough to destroy your shifter or ride with your foot pushing on the shifter all the time. If you had crashed and done that you would have noticed the issue right away.

Regarding swapping the clutch the actual swap is pretty much the same for all clutches. The difference is only in the pack measurement. You need the manual for your slipper to make sure it's setup correctly.
 

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Discussion Starter · #14 ·
I have a second engine sitting in my basement. It's actually the original engine. Previous owner had the teeth from the starter idler gear get shredded so he dropped a different engine in. The clutch it already out from him putting the yoyo in the new engine. I'm thinking of just making it a donor for the project. The detent wheel and everything else look to be in good shape. The shift mechanism will definitely be donated because it appears those are on back order. Engine had about 6k miles when it let go.
@MacBandit the engine hasn't been down on the left side at all to my knowledge. At least not the last several years and I dont rest my foot on the shifter at all.
@MadMel you dont happen to have the manual still? I'm going to email yoyo today.

Thanks again.


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For your shopping list above, consider adding new clutch springs - especially if they've never been replaced.

To me, the hardest part of clutch work is getting the cover back on with the fussy little alignment dowels, and making sure the spring loaded mechanism that connects to the clutch cable is in the right spot.
 

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Discussion Starter · #16 ·
For your shopping list above, consider adding new clutch springs - especially if they've never been replaced.

To me, the hardest part of clutch work is getting the cover back on with the fussy little alignment dowels, and making sure the spring loaded mechanism that connects to the clutch cable is in the right spot.
i was thinking about that. I've done stiffer clutch springs to several bikes in the past, but none that had a slipper. I'm not sure if stiffer springs will prevent the slipper from functioning as designed. Factory clutch springs are only about $4 each so it's not terrible.
 

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i was thinking about that. I've done stiffer clutch springs to several bikes in the past, but none that had a slipper. I'm not sure if stiffer springs will prevent the slipper from functioning as designed. Factory clutch springs are only about $4 each so it's not terrible.
The manual for the Sigma slipper says:
If you have a tuned 675 engine please use CBR600RR clutch springs!!
They are stronger and will prevent slip under power.
I just had a Yoyodyne installed with new stock springs though. I have stiffer springs from a Barnett clutch kit, but I'll stick with stock for now.
 

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My bike is dyno tuned, making 125 hp & 54 ft-lbs on that particular dyno. No issues with the stock springs for me.
 
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