The BSA A7-A10 Forum

Technical => Frame => Topic started by: duncan32bsa on 13.01. 2011 20:03

Title: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 13.01. 2011 20:03
Hi there,
Need help again!
As a change from very slowly rebuilding the gearbox, I thought I'd fit the swing arm to try to create some more visible signs of progress.
Naively, I thought this would be straightforward as it came out easily enough. Because I decided foolishly some time back to fit full width hubs I needed to change the swing arm.
Because I was having it powder coated, I fitted new silent bloc bushes (bigger ID) for the crossover shaft.
Now I have two problems.
1) There's a mm or or 2 of steel tubing protruding from the bushes which prevents the swing arm fitting back in the frame. Should I 'just' grind this flush back with the swing arm?
2) The hole in the frame is too small for the crossover shaft. The hole in the frame is about 5/8" and the OD of the shaft is 3/4".
I'm reluctant to start grinding/drilling in ignorance and would appreciate some guidance, please.
Assuming that I do solve this, what lubrication is needed?
I can provide pictures if needed!
Thanks for any help.
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: bsa-bill on 13.01. 2011 20:56
Gary there should be a mm or 2 of tune protruding at each side, this is what is clamped tightly against the frame ( I know it doesn't seem right but it is apparently)
You might need to spread the frame a bit to get the S/A in, sort of goes in on a slant then twist it straight.





Title: Re: Swing arm change from solid to hollow spindle
Post by: trevinoz on 13.01. 2011 21:03
Gary,
         You will need to open the holes in the frame to a close fit for the spindle.
Do not grind the silent bloc bushes as they have to be tight in the frame and bolted securely with the spindle.
You may have to spread the frame slightly to fit the swinging arm.
I fit the shaft through the bushes with a liberal coating of anti seize lubrication to aid the next dismantling.
There is no lubrication required as such as the swinging arm rotates by distorting the rubber in the bushes which are held tight in the swinging arm and between the frame lugs.
Trev.
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 13.01. 2011 22:03
Thanks guys,
tomorrow night's job! I'll let you know how I get on.
Cheers
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 14.01. 2011 08:57
Actually one thing that occurred to me is that I need the help of a rivet counter. (That's a compliment by the way).
The bike is registered as a 1960 GF and the frame number supports that (at least that it is an A10 from 1960).
I had assumed from the parts book that this would have had full width cast iron hubs as standard with a brake rod on the right. This would need a crossover shaft.
If that is the case why is the swinging arm pivot point on the frame only drilled out to take the smaller diameter solid shaft?

Can anyone help?

Thanks again.

Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: andy2565 on 14.01. 2011 09:18
be very careful when you open the holes out,the swinginging arm pivot point has to run true to the rest of the frame,1/2mm forward or up will throw the wheel out by nearly 4mm.not sure about the thickness of shaft but you should have a full width hub,maybe someone has converted it to the half width hub,i was going to do this conversion but have decided not to.
    just measured the hole for the crossover shaft on my frame which comes out around 20mm,
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 14.01. 2011 09:49
Andy,
My plan was to creep the diameter up using an adjustable reamer. Slightly dubious about it though, as I found reaming out the gearbox inner cover bronze bushes surprisingly difficult. The reamer kept digging in.
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: andy2565 on 14.01. 2011 10:00
if its possible,do one side,fit the swing arm,with the shaft in that side,then do some measuring,would be best with the forks and wheels fitted so you could check the alignment then file out the other side.never had much success reaming bush's myself,but reaming the steel hole should be easier,give it a go,16mm to 20mm is alot of reaming !
Title: Re: Swing arm change from solid to hollow spindle
Post by: RichardL on 14.01. 2011 14:32
I'm not so expert in each of the finite model specifics beyond the title year of my own bike ('55), and I'm on a train right now, so can't do research, however, I thought the 1960 Rocket Gold Star used the half-width rear hub. I assume you have a brake pedal pivot hole on the left where pillion loop meets downtube. Personally, if you have the half-width rear hub, it might actually be better to keep that setup. Rear brakes are less critical than front, as you know. Many have complained of spongy rear brake due to the cable connection (stock, it's not a rod). At this point you are choosing between a tricky ream job and a gruelling removal of silent-blocs. If you want a rod on the right, that's a whole additional task. BTW, the brake pedals are different, have acquired the correct pedal for full width? Anyway, saying more belies my claim of ignorance and might be wrong anyway. Anxious to hear what you will do.

Richard L, 
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 14.01. 2011 15:44
Hi Richard,
If I hadn't have had the FW hubs rebuilt on stainless rims already, I might seriously have considered sticking with the halfwidth. I have 2 swing arms still both silent blocs (one for each type of SA pivot) so it is a feasible option just an expensive one. This is what you get for advancing on a broad front! I'll double-check the frame number and the pivot hole positions when I get home.
It crossed my mind when I saw the small SA hole in the frame that there might be something dodgy with the frame provenance but
I prefer Andy's idea that someone down-converted the shaft dia in the distant past...
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 14.01. 2011 16:59
It turns out the registration document calls it 'a BSA'. The frame number is GA711035 which doesn't tie it to a model anyway. I guess I need the get the factory records to find out what it was originally. The engine number on the document (I have a different engine now) is DA1012974 which I read as a late 1960 GF. There is a brake pedal hole on the left.
Title: Re: Swing arm change from solid to hollow spindle
Post by: chaterlea25 on 14.01. 2011 21:33
Hi Duncan,
Heres how I kept the holes concentric when making them round again  after welding up, as they had worn oval !!
Before welding I made a template from a fairly thick piece of steel (8 or 10mm?) with a hole drilled in it the correct size
I tacked on some stops to position it in the correct place and then a 5/16 bolt and nut on the left side template into the swing arm pin end plate hole
I filed away most of the weld and finished off with suitable  sized reamer

Hope this makes sense????
John O R
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 14.01. 2011 21:50
Hi Johm,
That's sounds like an excellent idea.
Will try.
Cheers
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: trevinoz on 14.01. 2011 22:19
Gary,
          There a couple of possibilities for your frame.
Is it a CA7 frame restamped? Fairly easy to pick a CA7 frame as all the welds are gas welded whereas from about 1957 frames were electric welded.
Another could be a police special as were supplied to South Australia with a single sided brake in the rear and full width in the front.
Trev.
Title: Re: Swing arm change from solid to hollow spindle
Post by: minibsa on 18.01. 2011 04:45
I agree with Trev, I think you have a 1955 frame! My 55 has a frame No . CA7 105xx which was built Feb 55 so With all you describe I guess a PO has changed the CA7 to GA7. and the other frame numbers are possibly correct.
                       Bob.
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 18.01. 2011 08:50
Hi Bob,
Well, I've passed the point of no return now. I've reamed out the pivot holes to take the bigger shaft and the swinging arm looks nice and central at the back. Slightly dubious about the amount of metal remaining around now I've made the holes bigger - probably just over 6mm at the narrowest point.

Regarding John's suggestion, actually I have no idea how the tell the difference between a gas and an electric weld fillet. The fillets on my frame are neat and have a 'typical' ripple around the circumference. Maybe I'll post some pictures later.

If you were right about the frame provenance it might explain another issue I've got with the steering stem. The fork trousers are too short (6mm) to reach the bottom of the top fork yoke. Do you know if the 'steering stem holder' is the same depth on all these frames? If it was deeper than the 1960 one it would explain the problem. Of course, it could be that I've got the wrong trousers!

Cheers
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: iansoady on 18.01. 2011 12:59
Of course, it could be that I've got the wrong trousers!

Cheers
Gary

(http://viewyonder.com/wp-content/uploads/2010/08/wg_wrong_trousers.jpg)
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 18.01. 2011 13:11
He's the one I bought the bike off!
Title: Re: Swing arm change from solid to hollow spindle
Post by: trevinoz on 19.01. 2011 20:02
Gary,
            Does your frame have a sidecar lug in the left rear loop?
Check the gap between the battery platform mounting brackets and the frame cross member, it is different for CA7 and GA7 frames.
Trev.
Title: Re: Swing arm change from solid to hollow spindle
Post by: Brian on 19.01. 2011 20:56
Another small point, if you are going to use the cable operated rear brake dont forget to weld the outer cable stop on the frame before you get it painted.
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 20.01. 2011 20:03
Hi All,
I don't think it has side car lugs but then I don't know what they look like...
Funnily enough, there is a slightly larger gap around the battery tray than I would have expected - almost as though a small spacer is missing even though there isn't one shown in the parts books.
I'ver attached a general picture of the frame with the swing arm finally attached : ) I don't know if that helps roughly date it.
I've also attached a very poorly focused picture of the headstock welding for an opinion on whether it is gas or electric!
Regarding the yokes, I'm coming round to the idea that although the bottom one is probably the wrong p/n, it probably doesn't affect the yoke spacing as they all seem to be the same length more or less, going by the replies I've received from evil bay sellers anyway. I emailed Lauren at Draganfly about the length of the yoke 'trousers' and the gap I see and she has told me that it is definitely too short, even though for the life of me I can't see how it has been shortened. I have ordered a replacement part but I'm slightly nervous that when it turns up, it'll be just he same as mine. Lauren has said that the top of the trousers down to the centre of the lower clamp hole should be 20cm and mine is only 16.25cm. The strange thing is the hole for the headlamp top hat looks to be roughly the right distance from the top, judging by the pictures in the parts books. Soon find out.
As for the cable stop, the frame is already painted, so it looks like another thing to sort out : (
Thanks for all your help chaps.
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: trevinoz on 20.01. 2011 20:28
Gary,
           Having looked at your frame, I am fairly sure that it is CA7.
There is no sidecar lug in the frame loop and there is a large gap between the battery platform brackets and the cross tube which are CA7 features.
It also has no steering lock which was introduced in 1955 but has the cast front engine mount lugs which were brought in in '55.
Which centre stand do you have? The one for this frame is the one with the sharp feet.
I can't see which side the centre stand spring anchor is on but CA7 is on the right and GA7 on the left.
I would hazard a guess and say that your frame is gas welded, electric welded frames usually have a bit of spatter around the welds.
Trev.
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 20.01. 2011 21:15
Hi Trev,
THis is a pic of the stand prior to dismantling.
Cheers
Gary
Title: Re: Swing arm change from solid to hollow spindle
Post by: trevinoz on 20.01. 2011 21:28
Gary,
             The spring is on the right side as I suspected.
It looks like there is some sort of bodgie device to secure the spring to the stand, which is the later type.
I think the stand has been fitted wrong way around to lie up with the spring anchor.
I would suspect that the stand pivot point has been modified to fit this stand.
Fun, isn't it?
Trev.
Title: Re: Swing arm change from solid to hollow spindle
Post by: duncan32bsa on 20.01. 2011 22:08
Hi Trev,
Great Fun.
The main thing for me now is to make sure I can eventually convert it into the 1960 machine it is registered as!
Cheers
Gary
: )