The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: KeithA on 30.11. 2015 10:59

Title: A7 star twin 1952
Post by: KeithA on 30.11. 2015 10:59

Just wondering what the fitting is under the gearbox at the front close to where it bolts to the engine.
Its about a 1/2 inch bolt or tube, and sticks out about an 1'1/4", and has a locknut.
Sorry for the dumb question, but I can't find any reference to it in the exploded drawings I have.
Thanks in advance.
Keith Atkinson

Title: Re: A7 star twin 1952
Post by: Greybeard on 30.11. 2015 14:09

This is the detent device that locates the selector cam notches. In other words, it makes sure that the current ratio stays engaged until the rider changes gear.

Title: Re: A7 star twin 1952
Post by: trevinoz on 30.11. 2015 20:39

Or we could call it the cam plate spindle.

Title: Re: A7 star twin 1952
Post by: duTch on 01.12. 2015 11:51

 Sorry Trev, but I think GB has the call on this

Title: Re: A7 star twin 1952
Post by: Klaus on 01.12. 2015 12:50

Hi Keith,

keep them always clean. Over the years the plunger will stick in mud.
There is a little hole at the top of the plunger to allow  them moving in the oil.
Is this hole blocked, the down moving by shifting produce a vacuum inside.
So the spring could not get enought pressure to the camplate.
Result is the gear jump off by accelerat.


cheers Klaus

Title: Re: A7 star twin 1952
Post by: Greybeard on 01.12. 2015 13:04

Quote from: Klaus on 01.12. 2015 12:50

Hi Keith,

keep them always clean. Over the years the plunger will stick in mud.
There is a little hole at the top of the plunger to allow  them moving in the oil.
Is this hole blocked, the down moving by shifting produce a vacuum inside.
So the spring could not get enought pressure to the camplate.
Result is the gear jump off by accelerat.


cheers Klaus

Klaus, are you saying that the gear cam locator, (Detent) can get mud inside? I'm pretty sure mine has no hole in the bottom.

Title: Re: A7 star twin 1952
Post by: Klaus on 01.12. 2015 13:28

Yes, the swinging arm boxes have this hole.
It is about 1,5mm
So  l gues the the bolton boxes also.
I have made the experience with shifting off.
The manual sayed there will be only 2threads visible by screwing in.

cheers Klaus

Title: Re: A7 star twin 1952
Post by: Klaus on 01.12. 2015 13:39

Have made a picture.

Title: Re: A7 star twin 1952
Post by: Greybeard on 01.12. 2015 18:11

I think we may have a language misunderstanding here. I see that hole but that is inside the gearbox isn't it, not on the bottom and exposed to contamination, (by mud?). Maybe you are saying that gearbox oil sludge, (is there such a thing?) can get in there and cause the device to stick?

Title: Re: A7 star twin 1952
Post by: muskrat on 01.12. 2015 19:19

Gear control cam plate plunger housing!
By mud Klaus means sludge (oil & fine metal partials).
Without the hole it would hydraulic lock.
Cheers

Title: Re: A7 star twin 1952
Post by: Klaus on 01.12. 2015 19:47

Quote from: muskrat on 01.12. 2015 19:19

Gear control cam plate plunger housing!
By mud Klaus means sludge (oil & fine metal partials).
Without the hole it would hydraulic lock.
Cheers

Yes that's correkt.

Sorry for that misunderstanding *whistle*

Cheers Klaus