A7 gearbox question

[zitman]

Hi all,

The A7 is now running with its new clutch and the carburation sorted.

However on a test ride I noticed the gearbox is reluctant to select first gear from second.  It will sometimes go into neutral (not the proper neutral I think) and then jump in to first gear (a little disconcerting when the rear wheel locks up as a result).  The box also has more neutrals than the Swiss embassy!

When I had the gearbox on the bench I noticed the bolt holding the spring loaded  plunger affair was loose and just tightened it.  What kind of setting / adjustment is this designed for and what's the best way to set it up?

Cheers

Z

[BSA_54A10]

The detent plunger should only be tight enough to stop the cam plate flying straight past the proper spot and allowing the gear change pawl to return to the home position.
On older boxes it also helps the gears to stay meshed.
Slacken it back off.

[zitman]

Having had a brief poke about under the gearbox last night, the plunger is not even finger tight so will tighten it up at the weekend.

Still the bike passed its MOT today.

Z

[RichardL]

While running in reverse, I take it. 

[zitman]

Having got the bike taxed and MOTed I took it out on Saturday for a 35 mile run.  Selecting gears is something of a lottery!  Changing from first to second under reasonable acceleration often results in a false neutral, which I think is between second and third.  It' s also very difficult to engage first gear from second when moving.  One other symptom was that while travelling along in fourth gear it jumps back to third and then back into fourth, at first I thought the bike was misfiring but a prod on the gear level settled it down.

Any help on how to adjust this behaviour out would be appreciated.

Apart from the gearbox issues the bike was great, although the head gasket is blowing a little on the left but I will get a new gasket and sort that out.

Z

[RichardL]

Z,

Just curious, are you using a guidebook, like Haynes, for assembling your gearbox, or are you using your own experience (which, as far as I know, could outstrip the manual)? I had no experience whatsoever with motorcycle gearboxes and Haynes got me through it. As far as I can tell, mine (fully separated A10) works perfectly but for a little trickiness in finding "true" neutral.

Richard L.

[groily]

The jumping out of top and back (or sometimes finding a false neutral?) could well be an engagement problem with the sleeve gear. Was on mine anyway - the little dogs were very worn and the thing just kept slipping out of fourth. The sleeve gear bushes were shot as well, which was part of it.
Not the easiest things to repair, especially if the mainshaft diameter is much under spec where it runs in the sleeve. If the shaft is undersize it would need a pair of bushes making up having turned the shaft back to round. Which is what I had to do unfortunately.
Sounds to me as if the box needs a good seeing to for peace of mind, as there are obviously quite a few things not quite right. Good luck!

[zitman]

Thanks for the replies.

Richard,

I do have a Haynes comic but I have not actually had the gearbox apart.  I was really looking for some thoughts as to what the problem might be.  I am currently keeping an eye out for another gearbox, the workings of which I can strip and refurbish and then slot into the bike (or ideally the existing gearbox casings to save having to take the engine and gearbox out completely).

In all honesty I supposed I was hoping someone would say tighten screw X and its all going to be fine! 

Although it certainly makes riding the bike "interesting" I have ridden bikes with worse gearboxes (an ex Indian army Enfield springs to mind) and I enjoyed the 35 miles or so I did on it.  I still need to sort the head gasket and have the kick start lever re-chromed so I may well take a look at the gearbox when the kick start is off at the rechromers.

Groily: I will bear these points in mind when I do have the box apart.

Is it possible to get the innards of the gearbox out whilst its still in the frame?

Z

[BSA500]

Yes its quite striaghtforward to remove the cluster from the box,but all the clutch assembly has to come off as well(saying that if you remove the whole box the same applies).Some people find it easier to assemble the whole box on the bench but on the many occasions I have rebuilt the box its been in the frame.
Andy

[zitman]

Thanks Andy.

With all the grief I had trying to get the 6 spring clutch sorted and then fitting a 4 spring conversion, taking the clutch off is not a problem (done it that many times it takes about 10 mins now!).

Ta

Z

[groily]

Yup, did mine from end to end in the frame, and they're not at all bad to play with. If you're looking for a second-hand box, try George Yeoman's. Bit old-fashioned and not always there, but if I recall I googled and something came up. Can't find his tel no right now. I was thinking the same thoughts as you and found he had 2nd-hand boxes at about 80 pounds GB - but of course, hard to know what's in them. The worst fault is when the clutch-end of the mainshaft is messed up (so I'm told). Luckily mine wasn't and I was able to turn down the dia of the m/shaft about 10-15 thou, make a new bushing and fit the 2nd-hand final drive gear and adjacent mainshaft pinion. Only consequence is a slight whine in 3rd caused by non-mating bits, which is taking its time about going away (and may never). Otherwise, it feels great. Setting the cam-plate detent plunger is important though, per previous contributions, as is getting the clutch (mine's 4 spring) to give its best. That said, mine's done thousands of miles since its hospital appointment and is solid as a rock. There were reasons why grass-trackers and others often used BSA boxes I suppose.

[zitman]

Thanks for that Groily.  Hadn't thought of Yeomans, they are not that far away from me and I have bumped into him more than once at my local British Bike MOT place.

Cheers

Z

[BSA_54A10]

I would still suspect that detent plunger, they can take a bit of fiddleing with to get spot on.
Try doing it up 1/4 turn at a time ( it is very sensative) till you get the best change.
If you still can not get a suitable box operation then pull the box apart.

The others have all given you good and reliable information which I could not better.
However , there is another route you can take,
If the dogs on the gears are really badly worn you can get them recut and if you are going to get them recut then get them undercut 3 to 8 deg so that they dovetail together. This will give you a much more definate and solid gear change, well woth the $ 50.00 it cost me to have it done.
Bike Beesa
Trevor