How to clean transmission

[arseatea]

I rebuilt the engine on my 1967 CB72 Superhawk, that sat idle for 30 years, but I did not clean 30 years of oil gum from the transmission gears. Now the transmission will not shift. I have taken off the left side cover and cleaned and sprayed a little WD40 where I could reach, but I was afraid to use too much. It seems to shift ok with the pan off and doing it by hand, but after the pan is reinstalled, it will not. Is there a oil or additive that I can add to the transmission oil to remove all these gum deposits. I do not want to take this thing apart again. Thanks..Ron

[mike in idaho]

Pan? Do you mean the left side crankcase cover? Is the shift shaft binding when the cover is bolted down? You might check the neutral switch, located under the right side cover. If its cover gets dinged by a derailed chain or other damage it can bind up the shift drum and make gear changing difficult. These bikes have constant mesh transmissions, they don't shift easily unless the pieces are turning. I would just fill the crankcase with the right amount of oil and run it, then do a quick oil change to clean up the internals.

[arseatea]

Mike. Sorry, I did mean left side cover. I saw that mistake after I posted. Just wondering, If I can remove the shifter drum without splitting the case? Would any shifting forks and linkages drop to make it impossible to put it back in? If your other suggestion don't work, I may want to try that.

[G-Man]

You cannot remove the shift drum without parting the cases as you have to remove the fork guide pins to release the drum.

G

[arseatea]

Thanks for the info G-man. I was hoping for better news, but I guess a tear-down might be in store for me unless Mike's suggestion works..Ron

[cadman]

You can try SeaFoam of Marvel Mystery oil. I wouldn't run for lots of miles with it but run it a bit and then change the oil.

[arseatea]

Thanks. I use Marvel's Mystery Oil in the gas of some of my other engines from time to time, but never thought about mixing it with the engine/transmission oil. Maybe some other's have an opinion before I use it.