1985 k100 has worn shift fork

[curtis hiser]

I have a 1985 k100 with about 100 thousand miles on it. About three months ago from writing this post, the transmission started to slide in and out of second and third gear. I have disassembled the transmission to find the third-gear to fourth-gear shift fork grooved on only one side. I can not find any information on this in any forum or web searches. I have attached pictures to this post feel free to leave any thoughts. 

[duckbubbles]

Had the same thing happen many moons ago on my '85.  Wear of the shift fork so it does not fully engage the next gear and it slips out of gear rounding off the engagement dogs of the gears.  Shift drum and shift fork wear is the culprit.  Once the wear goes through the outer coating (anodizing?) on the drum/fork the wear is accelerated.  At the time I spent $1200 rebuilding my transmission (20+ years ago).  Doing all the work myself replacing seals, shift drum, a couple of shift forks, bearings and a couple of gears.  Might be less expensive now to find a  used transmission and pop it open to inspect the internals for wear before using it.  I fear there is no inexpensive way out of this.

 

Frank

[dirtrider]

10 hours ago, curtis hiser said:

I have a 1985 k100 with about 100 thousand miles on it. About three months ago from writing this post, the transmission started to slide in and out of second and third gear. I have disassembled the transmission to find the third-gear to fourth-gear shift fork grooved on only one side. I can not find any information on this in any forum or web searches. I have attached pictures to this post feel free to leave any thoughts. 

Morning Curtis

 

That is pretty typical of shift fork wear as it takes way more, & more constant, shift fork pressure to hold the slider IN gear than to simply slide it out of engagement for the next gear selection. Your wear should be on the engagement side of the fork not the disengagement side of the fork.   

 

That wear is typically caused by lack of back-cut in the engagement dogs (either due to wear, or not enough back-cut to begin with, or rounded ears on the shift slider or on the engagement dog corners.    

 

Of put another way, the shift slider engagement is not being held engaged under load by the dog to gear back-cut but is relaying on the shift fork to hold it engaged, that eventually wears the shift fork so it then can't hold the slider fully engaged so it pops out of gear.     

 

There are companies that can re-machine the slider & gear back-cut but probably not worth the expense on older motorcycles.

 

Another "good used"  transmission is usually the cheapest route even if you only use serviceable parts from the used transmission. The big problem is in finding a GOOD used transmission.