Old Honda Tranny Help

[radman]

Yo. 81 CB650C. Got for nothing in 3 boxes and a frame a couple years ago. Now a stock showstopper. Was in really nice shape (was given away for need of a headgasket, like they all need). Here's the deal-shes a softy on the upshift. Full travel on the lever will get the gear, if you're not in a hurry. Sometimes will give a false indicator, and a second movement will lock it in. Once in will never pop out. Downshifts are firm, clunky, and positive. Rpms make no diff. Clutch is new and solid. All 4 upshifts are like this. Motor was well lubed and spotless when I got this bike, no evidence of any abuse. Has approx 22,000 miles now, and problem appears to be worsening. Theres just no upshift feel to it, you never know if you got the next gear or not until the clutch is out and power applied. 90% of the time you'll have the next gear, but sometimes you won't, and theres absolutely no grind or other noise on the upshift. Ideas?

rad

 

[ionbeam]

Shift drum problem. Moves the shift forks, drum isn't supplying sufficient force to the forks on the upshift. Perhaps the shaft the gears ride on has a problem not letting them slide in one direction. Time to find a source for antique FSMs.

Shift Drum:

Trans:

Well heck, it's a good guess.

Alan

[edit] In the top picture item 6 is the ratcheting shift drum. Items 1 and 2 are the shift forks that push the gears together. [/edit]

 

[Ramblin Man]

The transmission is the last frontier for me. I know what it does, but when I look at one of those diagrams I just see a bunch of parts. I can't visualize it in operation and thats always pissed me off.

I need to get one of the "visible Transmision" models so I can figure out how it works.

Hell, better yet I just need to get a tranny to tear apart, and I think I have one in my driveway that I can use this winter.

 

[ionbeam]

I just need to get a tranny to tear apart

Been there, done that just a couple of weeks ago. A Honda no less. But no more, alas, in this case :lol: Once you have a tranny apart you have a box of gears but still no way to envision what is happening. The tranny only works when together but then you can't see the gears 'en lockum, springs ensproing and ratcheting slidems constantly meshing. Take it apart to see what’s happening and now the magic is gone.

Next time I have way too much time I think I can provide a simple working understanding. Very trixsey things goin' on but once a couple of functions are explained/illustrated it becomes much clearer. Free time should happen sometime around January here in NH

Alan

 

[dcarver]

shes a softy on the upshift. Full travel on the lever will get the gear, if you're not in a hurry. Sometimes will give a false indicator, and a second movement will lock it in. Once in will never pop out.

Hmm. Right up my alley. Anyone want to see what a Honda Xr600 tranny looks like? I'm into one right now. Too much horsepower = shredded 2nd gear set.

My money is on bent shift forks. One hard bang by an inexperienced rider or even a tipover where the gear shift lever imparts a load into the drum/forks will do it. The gears can't slide on the shaft, the drum is stronger than the fork, so the forks tweak.

Very common problem on older (70's vintage) Japanese dirt bikes.

 

[ionbeam]

Same problem with the 85 VF1100S tranny, bent 2nd gear fork. The hole in piston #3 trumps bent shifter fork though. Toast.

Alan

 

[radman]

Thanks guys. I can buy the forks more so than the drum being as it does it on all upshifts, not just 1-2 or 4-5 etc. I can't imagine the drum failing in all gears. Note that the bike never pops out of gear once in, regardless of throttle application. But once again, both forks, same symptom? Granted, the bent fork idea works as downshifts are clean and crisp-exactly as should be. I also thought just even wear on the up side of both forks, but the CB isn't famous for soft forks, and this bike was owned by my little brother, was well maintained, and he wouldn't have the first clue (or courage for that matter) as to how to beat on it. No obvious signs of any tip over ever, but he bought it when it was 3 years old. Everything in the trans linkage etc operates smoothly and quietly, no binding, noises, nada.

 

[ionbeam]

Shifter forks = problems one gear at a time. A stiff ratcheting shift drum can effect all gear changes in either direction. Also, the input gear shaft may resist gear movement in one direction but not the other.

Has this engine sat long enough to form mud in the engine case? The shift drum sits low, the shift forks and sliding shaft sit high. I see only one solution no matter what the problem is... Time to do the splits. But then again perhaps a bit of high detergency oil or super slick add-ums (all bad for the clutch) may free things up. Better to change the clutch than split the cases. Hopefully we will reach something like a DUH solution that only requires a minor adjustment to the shifter rod throw length. (???)

Alan

 

[radman]

Motor is absolutely pristine inside-the reason it was apart was the need for a head gasket-common on these, and so I had her down to the cases. Like all my stuff, it's been running on M1 15w-50 since I got it, with my usual anal change schedule. I've replaced the oe filter set-up with a CNC'd spin on-cooler adapter, until then, examination of the filter showed zero metal or other contaminants. 0 taper on the bores (still running std bore, original rings, 5lbs compression between cylinders). Thats why I'm kinda mystified as to the cause-this is the most unworn motor I've ever seen on a scoot. When she doesn't slip into gear the first shift, and I re-shift, she clunks in like a Feej-so the shift dogs appear to be excellent-the no pop-out would also indicate this. I'ts as if the shifter mechanisms simply aren't moving far enough to engage-but the absolutely silent up shifts also seem weird.

 

[charismaticmegafauna]

Take a look at #s 8, 9, 12, 16, and 19 in the diagram. There are trans shift help kits (offered for many bikes w/known shift probs for years) that strengthen the springs and have different size/shape parts/rollers, etc. Maybe a weak or broken spring on a part that's supposed to stop the drum. It sounds like the ratchet mechanism's doing it's job so that might leave the drum locating parts? In any event, it's accesable on the side of the engine and is way easier to check than splitting the cases.

Good luck , :blink:

 

[radman]

A shift kit ya say. This is a pretty low perf bike, and I haven't seen anything available for it in this respect, but, for what it's worth, you're the second person to suggest a look-see under the clutch basket. I may just be rippin into this bitch this weekend. Thanks guys.

 

[dcarver]

Radman,

Got to thinking again. Dangerous thing, thinking. Is it possible for a shift drum to wear on one side only? Say the right hand side is too wide. The pawl riding in that groove could prevent full travel of the shift forks. On the down shift, presumably the pawl would ride against the other side of the drum groove, and if not worn, down shift well.

Please post what you find this weekend after tear down..