Topic: Will not shift to 3 - really resolved :)

[RAFster122s]

Prokop, congratulations on the repair success!  It must feel great that your work has paid off.
Thanks also for the well documented issue and methodically approaching the issue.

David

[70CB750]

Thank you for the kind words, guys 

Did I mention I make my living doing validation and verification testing for last few years 

PeWe:  I would say it it was accumulated drag - surface quality of moving parts, lack of lubrication and low zddp. 

The history of the engine is unknown to me, got it from a guy who parted it out and kept the frame to build electrical bike 

Based on the valve guides I estimated 30 000 miles on it, since that's what I understand usually the 78F needs to eat them up. 

[PeWe]

Did you change oil (brand, viscocity...) when getting the gearbox to work? The first oil might be a bad one for a CB750....
I'm not asking for an oil thread with "best oil". More like "stay away" oil.

[70CB750]

Matter of fact I did.  The very first oil was Mobil Delvac 15W40 for diesels, my winter oil I used forever in the K0 with no problems ever.  Delvac is really great oil, I use it in my tractor and also in my 1986 Jeep for years.

But after opening it up again, I went with Valvoline 20W50 motorcycle oil (it was the plan from the beginning to use that oil) and it made no difference in shifting.  Only taking off the Neutral arm allowed me to shift 1-5 and back again.

[PeWe]

I'll work with my gearbox coming winter so I have to test the shifting before final assembly.
Replace 2,3,4 gears with undercutted ones.

[70CB750]

Same here, the K0 2nd gear is shot, I will be taking her apart to see what needs to be done to have the second again.