BA Gearbox Problem

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chris.shearwood
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BA Gearbox Problem

Postby chris.shearwood » Sun Jan 26, 2020 1:51 pm

My Sq4 with a BA gearbox was having a problem with occasionally popping out of second gear. With the box apart I haven't found anything obviously wrong or broken. I'll attach a photo of the offending gears. Are they worn enough to cause this problem? I kind of doubt it but don't have enough experience to say for sure.
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100_3575.JPG
1946 4G, 1950 NG and 1951 VH

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Re: BA Gearbox Problem

Postby JohnnyBeckett » Sun Jan 26, 2020 2:35 pm

hi have a look at your selector forks and your layshaft bushes and the gear change shaft it wears a lot and look at gear change selector most of my problems not going in to gear properly was the gear change shaft and the bushes i change the shaft and bushes now no problem going in to gear and no jumping out of gear :!:

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alan.moore
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Re: BA Gearbox Problem

Postby alan.moore » Sun Jan 26, 2020 4:19 pm

Chris,
Those gears look fine to me, the 'dog' teeth (the internal small teeth and those on the sliding selector gear) on mine were more worn than yours and my box stays in gear no problem.

The following may help.
Have a look at this Youtube video I did re the BA.
https://www.youtube.com/watch?v=plr2YoD ... dex=5&t=0s

As shown, the main gears themselves do not move only the selectors with the 'dog teeth' move.

At about 11 mins i show the box going into second gear. As you can see the sliding selector gear has to move quite a way to engage the 2nd gear so, for it to 'jump' out of gear the sliding gear must be moving out of mesh.

For each gear position the sliding selector is held in place by the bronze selector fork which itself is held in place by the pin/dowel in the camshaft slot.

The camshaft is held in each gear position by the spring loaded pawl, the pointed 'tooth' of which sits in one of 5 machined 'V' grooves around the camshaft. There is a separate 'V' for each gear position and neutral.

IMG_1285a.jpg


So as long as the pawl is firmly seated in its groove (and the spring is doing its job holding it there) the camshaft cannot rotate any further.

The camshaft is rotated into each gear position by the gear change mechanism in the outer cover. When operated by the gear lever the mechanism needs to rotate the camshaft sufficient for the Pawl to fully engage in the 'V' groove in the camshaft.

So thats how it should work. Common areas where wear can cause jumping out of gear are :

Weak pawl spring or worn pawl
Worn selector fork/camshaft slot/pin
wear in the gear change mechanism resulting in the camshaft not being turned enough for the pawl to fully seat in the 'V' groove (see attached PDF (last page) which explains where this wear can occur)



Hope this is of some help

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
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Re: BA Gearbox Problem

Postby nevhunter » Sun Jan 26, 2020 11:15 pm

You can get wear on the pins that are in the selector forks and wear on the fork faces themselves and excessive end float. The usual causes of flying out of gear is not going into gear enough or faces of the engaging parts worn off a bit or worn tapered . Mismatching of some model's parts can make a gear not go fully into place. The one generally affected is the gear on the mainshaft nearest the small ball race.(3rd gear) with the "bushed" version you must have the smaller end of the dumbell sliding gear recessed to prevent the shouldered bush stopping it going fully into engagement. Nev

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Re: BA Gearbox Problem

Postby adrian.hannam » Mon Jan 27, 2020 12:45 pm

You have probably read this old post, check the three rivets are tight. Worked for me.
viewtopic.php?f=4&t=9869&p=67865#p67865
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Re: BA Gearbox Problem

Postby chris.shearwood » Mon Jan 27, 2020 1:47 pm

Thanks to all who replied.

Alan, Thank you especially for letting me know that a gear box can work properly with gears that are in worse shape than the ones I have. I will be looking for the problem elsewhere although it seems that I may be dealing with a series of small problems which combine to create the popping out of gear. As I mentioned I haven't found anything obviously wrong but I haven't as yet spent much time investigating the foot change mechanism. The selector pins were new not so long ago and seem tight enough in the forks. Neither fork shows much sign of any wear and the pawl and its spring look fine to me. Thanks too for the link to your video. I have enjoyed watching it several times over the years. I think you did an excellent job on it.

Adrian, Your reminder about checking those three rivets is much appreciated. I think you may well be pointing me in the right direction to solve this problem

Regards, Chris
1946 4G, 1950 NG and 1951 VH

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Re: BA Gearbox Problem

Postby chris.shearwood » Mon Jan 27, 2020 5:41 pm

nevhunter wrote:You can get wear on the pins that are in the selector forks and wear on the fork faces themselves and excessive end float.


Anybody have any specs for camshaft and layshaft end float? I think Waller states between 1/32" and 1/64" for the mainshaft but I don't think he mentions the two other shafts.
In the following topic from about three years ago Paul Meredith wrote with regards to the camshaft: "Perfection is being free to rotate with no detectable end float."
viewtopic.php?f=4&t=6282#unread
Any other opinions out there?
1946 4G, 1950 NG and 1951 VH

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Re: BA Gearbox Problem

Postby paul.jameson » Mon Jan 27, 2020 7:18 pm

Look at the two pins which govern the selector mechanism, one of which is the end of the bolt which goes in through the kickstart cover. These pins can develop flats on them after time, which reduces considerably the overall movement of the selector. Look also at the plates which these pins bear upon. These also develop grooves in them which reduce selector travel. The simple solution here is to turn the plates over so that the unworn side bears on the pin and the worn side contacts the spring.
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Re: BA Gearbox Problem

Postby nevhunter » Mon Jan 27, 2020 9:36 pm

Chris, the layshaft float certainly may affect the depth of the engagement of the driving dogs. My answer to what is good is minimum safe, which I would see as about .010"( 1/4 mm) With new bushes /cases I've found without the gasket, the box sometimes hasn't enough end float. I've been fitting gaskets always lately. End float of the selector drum is not easy to adjust and the question always becomes which way does one move it, so I've just put up with it.
One thing that hasn't been mentioned is the fit of the "free" gears where they rotate on the layshaft. I have seen situations where there is considerable rock and looseness on the shaft. This will cause the gear to tilt and run misaligned and ease it out of engagement on a steady climb OR when running downhill as a brake. Nev

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Re: BA Gearbox Problem

Postby chris.shearwood » Thu Jan 30, 2020 2:50 pm

paul.jameson wrote:Look at the two pins which govern the selector mechanism, one of which is the end of the bolt which goes in through the kickstart cover. These pins can develop flats on them after time, which reduces considerably the overall movement of the selector. Look also at the plates which these pins bear upon. These also develop grooves in them which reduce selector travel. The simple solution here is to turn the plates over so that the unworn side bears on the pin and the worn side contacts the spring.


Paul,
Thank you for the suggestions. The bolt/pin that goes through the kickstart cover did have 3 thou of wear on it. (1.5 thou both flats). When I first assembled the box years ago I had turned the grooved sides of the four small plates towards the spring ends and since then there hasn't been much wear. It seems that my big problem of popping out of second gear is an accumulation of little problems so I've ordered from Draganfly replacements for most of the worn parts.
1946 4G, 1950 NG and 1951 VH


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