Just been out for a ride, only about ten miles, on my 1965 B40F. Beautiful day, great fun.
Something I'm wondering about: sometimes when I go to flick it into third gear, it appears to miss its gear and it's as though I'm in neutral. I flick it up again and it finds the gear. Could anybody explain that to me (a beginner) please?
Phil.
maybe selector fork worn
Any other possibilities?
I think it is not uncommon to find a "false neutral" when changing gear very gingerly.
If it changes when moving the pedal with a good positive movement into the next gear then this sounds OK to me.
I would be more worried if the bike jumped out of gear when driving which would then definitely need some further investigation.
Most if not all of the old Brit bikes I have owned have suffered from the odd false neutral ( and even my relatively modern BMW )!
Okay thanks Adrian, maybe I need to be a bit more positive with my gear change. I'll try it and see how I get on. Phil.
Slow and firm, letting the revs drop before engaging then next gear.
Just out of interest, a couple of things I was wondering (having been reading the very basics of how a motorcycle gearbox works):
1. Chaz suggests wear in a selector fork. What part would wear? The peg that fits in the groove in the shift drum?
2. Adrian and Mark suggest changing gear more firmly in order to prevent a false neutral. I'm not really sure what a false neutral actually is, but was wondering: when trying to change to third gear, why might changing gear gingerly result in a false neutral? If third gear wasn't found, I guess that would be because the selector claw was not moved far enough to locate? But if that were the case, then wouldn't the pawl spring simply return the drum to where it was, meaning we would stay in second?
I'd appreciate any information/explanation which might further my education!
Phil.
When you are changing gear, the foot pedal is linked to an indexing plate inside the gearbox. This moves the selector forks which in turn moves the gears along a shaft. The gears have "dogs" - prongs sticking out to engage into the adjacent gear. The dogs have to be fully engaged in the adjacent gear or it will not engage properly. There is always a degree of play between all of the components so if the gear has not been moved enough it will spin resulting in a false neutral. I don't know if this makes sense. In reality a couple of gears are usually moved when changing gear ( there are 2 selector forks ) and complete engagement of the gears has to occur for a change of gear. Also, the cam plate ( indexing plate) may "stick" between 2 gears which may also result in a false neutral. If you jack the back wheel up in the air and spin it and change gear by hand with the pedal, just note how much movement occurs before anything happens. This is the play and working clearances inside the gearbox.
I don't know if this makes much sense - I'm sure someone could explain it better.
I have a Bantam and often find a "false neutral" between 3rd and 4th gear. I rebuilt the gearbox to what I feel is a high standard and it still happens!
Okay so I guess there is no selector drum in these gearboxes. That's a shame in a way because I'd just about got the basics of how it works. I don't know how the indexing plate moves the forks but I guess if ever I need to delve into the gearbox then I'll see. There are a few Youtube videos on line showing how motorcycle gearboxes work but they all have a drum which moves the forks which of course move the gears. These BSA boxes don't appear to have such a drum. I don't suppose there are any videos showing how an indexing plate style gear change works? Phil.
with the plates they do wear.
there are a series of slots, one for each gear plus neutral and two spring loaded fingers that operate the cam.
the plates can wear and the fingers could fall in also the fingers springs can get weak.
on our B40 the cam plate( as its called) pivots on a shaft which is in place in the housing of bare metal. ours is fairly worn and thinking of a bush thats thin enough to reclaim as needle rollers are a bit on the big side.
all this play does not help..
Bloody finger springs!
Mine broke in a C15 gearbox in the 70's. Gearbox then drops into 4th gear. Ending up having to push the bike 5 miles home.
If I remember correctly there was only 1 spring in my gearbox. Went to Fred Hanks shop to get a new one and he suggested putting 2 in place of the 1 spring. He said they rarely fail if 2 are put in!
Hard to imagine what the plate system is actually like, not having seen one in the flesh. But thanks anyway. Phil.
https://www.draganfly.co.uk/bsa/bsa/b40/category/1186-1186-
selector forks #15
camplate #16
finger and spring #25/26
https://www.draganfly.co.uk/bsa/bsa/b40/category/1185-1185-
the flat sides of the selector forks push and pull against the sides of the gears to slide them inn and out of mesh. when one gets bent they sometimes dont fully engage, bearing in mind the force on the pedal it is common to bend the fork arms
This occasionally happens with my Velo, the advice was to hold the gear lever down (or up!) until the clutch was out.