General question about the gearbox - cam plate spindle screw adjustment?

OK '66 N15CS. I plead ignorance, this was the first gearbox I've rebuilt, full stop Now, it shifts OK, and some issues I am experiencing may be the nature of this beast. It's not terrible but I hope to improve. I had a '66 Triumph which had short snickety-snick throws and easy engagement. Expectations may be too high. It's just... not... great. I want to sort it out if possible, but can live with it if it's how they are.

I took great care rebuilding the gearbox, and it functions without leaking or jumping out of gear. But it (1) takes long, deliberate shifts (2) has a false neutral between 2nd and 3rd, and (3), sometimes (rarely, if not deliberately downshifted) gets caught in an intermediate state where it is clacking - ugh, metal on metal gear noises ensue.

When rebuilding, I recall that the gearbox seemed very sensitive to the two screws that are on the forward end of the box - the cam plate spindle screws. I also recall having leakage problems with the O-rings that were supplied with the Andover Norton kit and had to fix those using different O-rings. Anyway, the leaks are solved, but .. is there an adjustment to these cam plate screws that must be made? It seems (from memory) that if I back them out things loosen up and get better, but I don't want them to rattle out. If I recall correctly they are sort of acting on a spring but I can't see it by the diagram - it's been a while and I forgot. I think they are screw and washer 22/21 which go into O-ring and bush 12/20.

Are these adjusters in some way? They seemed to be but I haven't figured it out. Any help is greatly appreciated, the bike is fun to ride and I'm working out the inevitable teething issues and learning how she goes now that she's alive again.

These bolts should be fully tightened.
Maybe too thick O rings?
Did you change the bushings (20) ?

I regard the AMC gearbox as the easiest shifting from that period. Just my opinion.
I overhauled one a couple of years ago. I remember that the position of the bushings (20) was a bit tricky to figure out. They determine axial position of camplate and quadrant. Also affecting O-ring seat.
So if the bushings are pressed in too long, you get a leak. Might be your problem with AN O-rings not sealing. L'm not certain how shifting is affected by bushing position.
Also remember that the spring (25) length and stiffness is critical to pleasant shifting.

Mike40M said:

I remember that the position of the bushings (20) was a bit tricky to figure out. They determine axial position of camplate and quadrant. Also affecting O-ring seat.
So if the bushings are pressed in too long, you get a leak. Might be your problem with AN O-rings not sealing.

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If pressed in too far or the bushings are too long, they can push the camplate too far towards the shifters and/or he quadrant to tight against the camplate. If simply push in too far, that causes the spindle of each to be too far into the case - the washer must be clamped to the end of the spindle and it must put some pressure on the o-Rings.

I recently worked on one that both were pressed in the correct amount for the washer/o-Ring to be fine, but the bushing for the camplate was a little too long and was pushing on the selectors causing it to take too much effort to shift. The bushing for the quadrant was way too long so the quardant was pushing very hard on the camplate increasing the problem. I have no idea where those bushing came from, I didn't install them. Rather than replacing them, I filed them down to get proper clearance.

This was for a later gearbox so I'm not sure if it is the same but probably is.

OK thanks, I'm going to absorb this helpful info and have a look.

Through the fog of time, I recall the O-rings were an issue others had encountered and I had to purchase some slightly larger ones. I think there was a forum post on that subject which led me to do that. I also recall paying attention to getting them pressed in the correct amount. Only one leaked, perhaps due to the oil level difference. I may be confused on whether I found this to affect the shifting but good to know it can, so I will double-check these.

And now Mike40M triggered my memory that when I hand-shifted it on the bench, tightening up that index plunger affected the resistance to shift more than I thought it should (just generally observing based on other gearboxes action). I will take a look, maybe that spring got stretched previously - I have read that has been done as a patch when a box jumps out of gears. Thankfully I can do these checks in situ.

ludwig said:

These bolts should be fully tightened.
Maybe too thick O rings?
Did you change the bushings (20) ?

Click to expand...

When the bolts (22) are fully tightened do they rotate in the bushing when the gear lever is operated? Thanks

Desburnett said:

When the bolts (22) are fully tightened do they rotate in the bushing when the gear lever is operated? Thanks

Click to expand...

yes they do