Topic: `75 CB750K popping out of 2nd gear

[Racegun]

Hey everyone, my bike constantly pops out of 2nd gear and sometimes the shifter gets stuck between 3rd and 1st.

I'm forced to skip 2nd gear so I just go from 1st to 3rd.

Any thoughts on what is wrong? My initial thought is bent shifter fork?

Is there any path to fix this without taking the motor out of the frame?

[ekpent]

 You probably have two gears that are no longer staying meshed together. Its the worn dog syndrome where two gears slide in together and the 3 posts that slide into the other gears slots are rounded/damaged and not locking together. Fixing requires splitting the cases and a shift fork may be bent or worn along with that also.  Not a rare problem.
  Here is a picture of member Hondaman holding a worn one. Check the shifting mechanism under the engine side cover first though just in case something is not right there

[PeWe]

Gear 2 and 4 are the typical jump out of gears.
Complete transmissions are often sold cheap on eBay USA.
Engine out, cases apart.

Maybe time for a restore anyway?

When it is out, check the internal chains and tensioners that have rubber wheels thst can be hard as bakelite falling into black pieces found in oil pan.

Primary chains have a max slack measured from below with oil pan removed, max 70mm between oil pan mating surface vs primary tensioner flat surface. New chains 65mm.

Engine out to fix things is a pandoras box of possibilities!