Stuck in gear

E

eabergman

Full member
My SF1 was off the road for a long time, needing a top-end job. I finally had Scott Potter do that plus a functional restoration. When I started riding it, however, there was a shifting problem, difficult to shift, more or less stuck in second gear. I discovered the locknut on the shifter eccentric was loose so I figured a quick adjustment would put things right. I've done this job on both my 750s and the Jarama before. I've got the rear wheel lifted and sparkplugs out, turning the engine at the crankshaft nut. The gearbox was in neutral to start. pushed down into 1st, on my way to 4th for the fine adjustment, but it won't come out of gear now. I can't get back to neutral. I can turn the engine/gearbox/rear wheel from the crankshaft or the rear wheel without hearing any funny noises but the shift selector refuses to move with what feels like a reasonable amount of force on the shift lever.

Ideas welcome, especially ones that don't begin "First you'll need to split the cases?"

Eric
 
One of the springs in the shifting mechanism is broken I think...
Happens some time, I always have the sprins in my tool set on the bikes.
 
First port of call is to lean the bike over to the left against a wall or use a support of some sort (to keep the oil in) and remove the gear selector cover. I reckon you'll spot the prob pretty quickly in there. Could be the spring, could be summit else. Doesn't sounds like 'split-case-material'.
 
I wasn't clear, I guess. I do have the gear selector cover off and have inspected all the bits inside. That's when I noticed the locknut on the eccentric was loose. Other than that I see no problems. The spring is in one piece.

Eric
 
Check that the big spring isn't getting caught between the slot in the fork and the eccentric pin. I fit a washer behind the big spring to ensure that this can't happen. You then need to check that the cover doesn't bind in any way once it's screwed up tight. I check it without a gasket, so I know exactly how much clearance it will have once fitted - the selector 'drum'? (with the pins in it) obviously can't be checked for sideplay with the cover in place, so a no-gasket check works.
 
Are all the pins still in the selector wheel-like thing, is that wheel got the mark on its edge set to be horizontal? The excentric should be adjusted in 4th gear as that is where the hook can be seen with it centralised. Do you have a Green book, that has the best description of this job. I shouldn't talk, I have had mega troubles doing this. The usual issue is either lot getting 1st or 5th gear. Not being able to move the lever is not typical. Can you remove the large shaft the hook-like gadget is connected to and move the other bits with a lever to change gears?
 
I'm assuming that the shaft with the pins was never removed from the selector case? And the shim type retainer washer is still on the outside so the pins can't fall out. If that 'drum' with the pins has been removed, as Vince says, you need to ensure the marks align in neutral, looking through the hole to where the two selector gears mesh.
 
Yes, all those issues have been covered. I have the Green Book and I've done this job successfully a number of times. This is not a problem of the adjustment being off and having sloppy gear changes. The gearbox seems to be stuck in first gear. I can put plenty of force into turning the selector spindle (25) to put the gearbox into neutral but it won't budge. I'm using the terminology and diagram number from the parts book (Table 8) for clarity.

The selector spindle (25) has been removed and replaced several times at this point but I checked the alignment with the inside mark on the face of the driven gear of the selector drum shaft (24). All pegs (17) are in place. I'm trying to shift with the cover off, so there is no binding. The spring (34) in the selector arm (29) is working as it should and is not tangled with the eccentric screw (19). It seems that something is keeping the selector drum shaft (24) from turning.

I've heard of the spring (33 breaking but I don't know if that could cause the gearbox to be bound up like this.

Eric
 
Hi Eric,
I'd start by asking Scott exactly what he did to the bike.
Unusual for the selector eccentric nut to be touched during a top end rebuild.

Paul
 
Can you move the shift drum shaft that comes from the gearbox into the selector cover? When turning this shaft (it is hardened steel so tolerates careful use of good grips but don't overdo it) the only resistance should be the sprung locator roller that holds it in each gear. If the spring is broken it will be floppy and won't stay positively in position. Simply turning the countershaft sprocket backwards and forwards to let the dogs line up you should easily be able to select every gear if everything is correct inside the cases, if not it looks like...... The only other thing bearing on it is the neutral switch, which may need to be shimmed with different thickness washers, try removing it and see if things free up.
 
Excellent suggestion about the neutral switch. Considering what Scott did on the bike (full rewiring) I think it's pretty likely he had that switch out, but I don't think he went into the selector mechanism. I think I asked him if he'd had the bottom end apart for any reason and the answer was no, but I'll confirm it with him. I'm guessing the locknut loosened on it's own over time. I didn't check the adjustment before messing with everything so I can't say if it was in a bad position or not.

Anyway, Scott is actually in residence in Denver these days and he is stopping by this morning to have a look at it with me.

Eric
 
Solved. It wasn't the neutral switch, but in the process of testing again after removing it I found that the straight arm of the selector spring (35) was just getting caught between the eccentric screw (19) and gear change spindle (22) on up-shifts. It's very hard to see, but when I removed the spring the gear change works correctly again and I can see some scratches on the end of the spring arm where it was hitting. I will shim the spring out a little to ensure this can't happen again. I will also install a new spring. I think this was the problem I first noticed when I was test riding the bike too, difficulty in up-shifts.

Thanks to all for suggestions.

Eric
 
eabergman said:
Solved. It wasn't the neutral switch, but in the process of testing again after removing it I found that the straight arm of the selector spring (35) was just getting caught between the eccentric screw (19) and gear change spindle (22) on up-shifts. It's very hard to see, but when I removed the spring the gear change works correctly again and I can see some scratches on the end of the spring arm where it was hitting. I will shim the spring out a little to ensure this can't happen again. I will also install a new spring. I think this was the problem I first noticed when I was test riding the bike too, difficulty in up-shifts.

Thanks to all for suggestions.

Eric
Click to expand...

To prevent this happening, there should be a thin washer placed on the shaft over the spring, before the cover is fitted.  Often missing.

piet
 
Hi Piet,

That outer washer was in place but apparently there was still enough play to allow the spring to get caught. After I added the shim behind the spring I found that there was no axial clearance when I fitted the outer cover, but I substituted a 0.5mm washer (normally for the neutral switch) for the outer washer and then I had some clearance back. I just buttoned it up a short while ago, but I need to do a few other things before I can do another test ride.

There isn't much on a 750 that I'd call "fiddly" but the gear shift mechanism is near the top of the list in my experience.

Eric
 
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