Gear change lever sticky problem- really confusing

[feltzo]

So my baby has always shifted smoothly, no problems going up or down.
The other day I got a proper starter button hooked up, and immediately the starter reduction gear blew up, so it looks like I'll go without that for a while.
I took the side covers off and cleaned it out, and the elbow-shaped gear arm that connects to the gear change lever pinion became dislodged, I got it put back in the right place, shifted through the gears with the cover off, everything was good.
But then I got it gasketed up with liquid gasket (a temporary fix, don't worry) and tightened it down. The next day I tried to take her out and then it wouldn't shift at all. I took off the cover, looked fine, tried shifting with the cover off, and it worked great.
Now here's the confusing part to me: It shifts fine until I tighten the screws on the cover. I noticed that with all of them tightened, the gear arm is sticky and doesn't shift down well or at all, but if i loosen the one or two screws nearest the gear lever, it shifts just fine.
Anybody have any idea what's going on with this thing? It just got nice here in MN and I wanna take her out. Thanks.

[TOOLS1]

What model bike is it?
TOOLS

[feltzo]

1975 CB750F

I messed around with putting the different length screws in different holes (cause I was dumb and didn't lay them out as they were), and I got it working okay enough so I could ride it. It would fly through the gears during acceleration, but shifting down was a whole other story. It would take multiple kicks before I would feel it shift down a gear.

Could it be as simple as greasing the rubber grommet on the shift lever bolt? The thing that really confuses me is that it shifts perfectly until I tighten down the screws nearest the shift lever bolt.

[TOOLS1]

Without looking in it, I would say you have something out of place, and when you tighten the cover down it is pinching something.
TOOLS

[feltzo]

When I took the cover off, the only thing that came out of place was the elbow-shaped arm with the spring on it that goes from the gear change pinion/bolt to the gear selector drum (sorry for the inaccurate dumb-man's terms). I got it put back so that it shifted just fine, and it looks right compared to the dark, blurry and upside-down photo the clymer's manual has, but it's just when I tighten it down that it starts getting crappy. Is there a washer on the gear change pinion that maybe fell off?
I can post a pic tomorrow of what it looks like without the cover on. Idk if that will help though, because everything works fine when the cover is off lol. It's always something with these bikes, I tell ya.

[zedx]

This exact same thing happened to me the other day. I noticed when I loosened the 2 screws around the shifter it worked smoothly again. I ended up taking the whole thing off again RTVed it and just left those 2 screws not quite as tight as the others. No leaks as of yet and seems to be working properly. I was thinking that maybe because there wasn't an actual gasket in there that it was pulling up to tight. Gasket is on order.

[feltzo]

Ha weird that we're in the same exact boat. Glad I'm not the only one. I just ordered up some gaskets too. I'm gonna try cleaning off the RTV and then bolting it on gasket-less and see if it shifts fine when tightened down. Then I'll put on the gasket if everything seems in order. I'll let ya know what happens.

[shinyribs]

Hmm,,this sounds kinda tricky. But it must be something simple. The are brutally simple machines, they don't run super tight tolerances on these shifter components,but they are accurately built and require a careful eye sometimes.

First things first ,though: Pleeease don't run without a gasket. No gasket=oil leak=slippery back tire=

The first thing that comes to mind is how the shifter shaft mounts in to the case. It just slips in to a bushing in the engine case and the shifter cover supports it with a bushing as well. It possible that the shifter shaft is not fully seated somehow, allowing the shift cover to pinch something.

It may not be the shaft itself, it could be some part of the linkage itself.

The stud that all the shifter parts mounts to (with the multiple washers/springs) may have something out of order causing it to bind on the cover somehow,but I really don't recall those part running close enough to the cover to do that. The tip of the stud that the nut goes on protrudes the furthest of anything, and it obviously clears the cover just fine as it is.

Something has to be hitting the cover and getting pinched. It's the only thing that makes sense.

Are there any scratches or witness marks on the inside of the cover? That should give you a clue.

But please...no silicone...and no running without a gasket.

I'm usually pretty good for throwing caution to the wind, but these are two things I wouldn't dare do in this situation.


Good luck fellas. Keep us posted on what you find,please.

[feltzo]

No worries, I won't be riding around dumping oil all over the place. I was just gonna peel the crappy silicone gasket off and bolt it on and see if it shifts smoothly by hand. Then I'll put my new gasket on when it shows up in the mail.

It's so bizarre. Just playing with the lever by hand, it works fine until the two screws nearest the lever are tightened all the way.

Get this: So after I play with the lever with the screws tightened down (when it's not shifting consistently and doesn't move easily), I then loosen the screws nearest the lever and can watch the shift lever jump back into the center position, the way it should be.

The thing always worked fine until I took the cover off, and the only thing that moved was the end of the lever arm, just kinda swung down and I put it back into place. Hopefully me and ZedX can figure this out.

[feltzo]

Did the gaskets help your situation at all ZedX? I'm waiting to get mine back from the shop right now.

[feltzo]

Put an actual gasket on, and it works just fine now.

Turns out, the cover presses too hard against the engine, squeezing the shifter lever pinion and making it sticky. It's because the RTV squishes to almost nothing, but a gasket is like a .002" shim.

So kids, as if you needed yet another reason to never use RTV silicone gaskets, here ya go.

[LukeM]

Just goes to show you how fine the tolerances are with these bikes.  Designed with slide rules and paper drawings.  Amazing.

Glad you figured it out.  Now, on to the next thing.
Luke M