I'm slowly tearing down my CT175 engine (taking lots of pics and bagging parts).  Just about ready to split the case with my new tool and realized something loose inside.  When I removed the neutral switch and the large adjacent hex plug, I got this small chunk to fall out.  Anyone recognize this and know what parts I should expect to replace?  Remember, I got this bike as a non-runner due to seized piston, but it was free enough to push it through its gears so I thought the insides were ok....Thanks for any eyeballs,Joe M (Santa Clara, CA)

Thats got me stuffed, just when i thought i knew everything--know nothing. Should be a ball & spring with the bigger hex for neutral detent, & other one is neutral light--not shown but in the electrical pic i guess. Hard to imagine something like that coming out of either hole as selector drum runs close to both holes. Sure it wasn't something sitting close by & fell on the floor. Hell i'm lost so hope someone puts me on track please.
www.partzilla.com/catalog/yamaha/motorcycle/1970/ct1b/shifter-1

Ok i now think it might be a Dog of a Gear. Still can't see how it could come out one of those holes though. Possibly a dog with a bit of gear of number 18 in the link.
www.partzilla.com/catalog/yamaha/motorcy...70/ct1b/transmission

Are you sure it didn't come out the drain plug underneath. Be interesting to see inside when you get there. Looks like a weak point in an otherwise great gearbox.

Yep its this one. 

Thanks RT - you found it! - one of those 5th gear pegs.  Not at the engine right now so maybe the drain plug *is* out.  I can imagine your questioning if even possible to drop out of the neutral detent and switch holes.  I was shaking the engine every which out of curiosity...originally thinking (like a newbie) it would drop out of crankcase.....then thinking about the neutral bits I had just removed.  I'll get the cases opened later today and see what else is going on.
Thanks again,.....

Yep i think 'that' breaking off would be a 'first' on this site & be interesting to know. Does look a weak point though. Worried about my AT1 now haha. While i'm at it--i don't suppose its thrown a chain which nearly always wipes off the ent of the selector drum where it extends above the sprocket in a 3 screw cover. It'd be obvious as cover would be smacked off. If that happens it lets the selector drum float sideways & can 'try' to pickup two gears at once with dire consequences. Had it on farm bikes mostly 100's.

Hello - Finally got out the gearbox and shifter parts.  Other than the broken parts, no other damage.  Its mating gear "holes" are beefy so all is good, and chunk apparently dropped free quickly without getting caught up in the works.  Not related, but my 2nd gear (the second smallest off all gears) has noticeable brinelling...maybe even some spalling (I looked up some metalurgical terms!).  For an old bike, do people just use as-is, or try to find something better than mine?
Thanks, Joe

Ha, i was going to google the words. But looks obviously through the hardening so it's downhill from here. It'll carry on as is of course but not good long term. How is the gear it drives onto for tooth damage?. The little gear is pressed on--& off. I've seen them let go on scooters that ran that pressed on idea. Not a good plan from the factory. If you're pressing it off then you'll have a new tight gear to press on so it'll be good.
So, answer 'is', now you know how to get it apart it'll be easy next time if you decide to carry on as is.

Yeah I think I will replace that 2nd gear also.  Its larger mate appears ok like all other gears.  But curious why the little second gear is more worn than the even smaller first gear (machined into main shaft).  Maybe different hardening or 1st gear gets less use/load than 2nd gear?
Regards,
Joe M

RT325 FTW!  Again.  As usual.