Author Topic: Gearbox conundrum  (Read 333 times)

Offline a101960

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Gearbox conundrum
« on: 01.07. 2018 14:55 »
BSA A10 gear box. Got a problem that I can’t seem to get to the bottom of. Initially when I first go for a ride and everything is cold, the gear change is noiseless and smooth. Selecting neutral from either 1st or 2nd gear while stationary is easy and reliable. After everything has warmed up selecting neutral becomes very difficult, and the best way I can describe it is that gear shift almost feels as if it is seized solid and will not select neutral at all. This happens after about 15 miles or so. I have replaced the selector forks, and “claw” in the gearbox, and spent a long time setting up the clutch with a dial gauge (four spring clutch with SRM ally pressure plate and radial bearing fitted to the clutch push rod). I have replaced the clutch springs, cups, and spring adjusters too although these symptoms were there before I replaced these items. Gearbox oil is 50 weight and primary chain case has ATF in it. While riding along the gears change just fine, and it is not until I stop and try to select neutral that I notice any problem. I am lost as to what to investigate next. Anyone got any ideas or suggestions as to what might be the cause of this problem? It has been suggested to me that this could be due to excessive  main shaft end float caused by a worn bearing. I am guessing that the one shown in the image (item 14) on the drawing is what is being referred to. Any opinions on this? And if this is probable exactly what is meant by worn?  I am totally mystified by what is going on not helped by the fact that I know nothing about gearboxes in general and A10 gearboxes in particular.

Offline duTch

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Re: Gearbox conundrum
« Reply #1 on: 01.07. 2018 15:10 »

 The only way I can see you'd have excessive end float (ie; any more than none), is if nut #21 is way loose, or if circlip #15 is missing...other than that, it's still a caborundrum.... *conf2*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Online morris

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Re: Gearbox conundrum
« Reply #2 on: 01.07. 2018 15:27 »
Sounds more to me like your clutch is dragging.
Already when cold my SA four spring clutch didn't turn smoothly even with no plates in it. I tried it like that anyway but I suffered the same problems as you have. Worked reasonably well when cold but as soon as things started to heat up had difficult gear changes and couldn't find neutral at standstill.
In the end I turned the adaptor down by a couple of thou to give more roller clearance which, in combination with an SRM pressure plate completely cured the problem.
Wear in the timing side bearing should be massive and very noticeable before having an influence on the gear changes.
One thing to check is that the clutch lock washer tab (the tab that's bent inwards and grabs on the inner basket) isn't too long and pushing the inner basket out of true! (DAMHIK)
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Online JulianS

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Re: Gearbox conundrum
« Reply #3 on: 01.07. 2018 15:35 »
I too suspect clutch problem.

The bonded clutch plates do expand a bit when hot increasing the clearance between the push rod and pressure plate.

With an SRM pressure plate you should not need to use a dial gauge they are very easy to setup and very reliable.

Is there more slack in the cable when hot?

What are the tabs on the plates slots in the hub and chainwheel like.

How much wear between clutch arm and gearbox outer cover, too much causes reduction in lift.

With the 4 spring sometimes a spring pin will be stuck between chainwheel and inner drum on assembly.


Offline a101960

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Re: Gearbox conundrum
« Reply #4 on: 01.07. 2018 19:27 »
Quote
Is there more slack in the cable when hot?
No cable slack is the same it does not change.
Quote
What are the tabs on the plates slots in the hub and chainwheel like.
No obvious signs of wear that I could see when it was all apart.
Quote
The only way I can see you'd have excessive end float (ie; any more than none), is if nut #21 is way loose, or if circlip #15 is missing...other than that, it's still a caborundrum
Everything looked good when I last looked, I suppose I could look again. Sounds more to me like your clutch is dragging.
Quote
I agree it does. Back off the springs a tad maybe? We have some lovely motorcycling weather right now, but I just don't want to ride it, because I am getting no enjoyment from it. BTW chain tension primary, and final drive are O.K. All I can say with certainty is that I know something is clearly very wrong.

Online bsa-bill

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Re: Gearbox conundrum
« Reply #5 on: 01.07. 2018 19:56 »
I'd suspect clutch as first suspect as well
Random thought would be the indent spring if you had moved it, but can't see that fitting in with temperature change in any way
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco