Author Topic: Trying to understand what's wrong (rear wheel offset)  (Read 568 times)

Online morris

  • Wise & Enlightened
  • *
  • Join Date: Aug 2012
  • Posts: 1544
  • Karma: 23
  • Antwerp, Belgium
Soon after I got the SA it was clear that something was not entirely right at the rear end. Not that it was behaving weirdly, but there was something bothering me about the position of the wheel towards the frame.
Some measuring lead me to conclude that the wheel's offset wasn't right.
The measurements I made showed that the wheel should be moved 5 mm to the right to have it centred between both legs of the swingarm.
As I recently had to pull on a new tire, I decided to loosen the spokes and re-tightened them with a 5 mm offset.
Happy as I was with the job done I mounted the wheel, but because the saddle and mudguard where off, I immediately noticed the wheel was still not centred to the frame... *conf2*
Now to the point; I did some investigative measurements and found that the swingarm sits about 4 to 5 mm left of the frame's centre. Is this normal...? I wouldn't think so, but then I can be wrong...
I have measured the distance between the frame plates, which is 236 mm (corresponding to 9.291") .The book says this should be 238 mm (9.373)
I also notice a small gap, maybe 0.5 to 1 mm max. between the right plate and the swingarm tube.
But all of this added up still don't explain the 4 - 5 mm difference.
Is it possible that some PO cut off a part from the tube to make it fit between the frame plates, or could this swingarm be from another model? If so, then the inner shaft has to be modified also, as there is no surplus thread sticking out at the nut
Or can this just be wear???
Thanks in advance for your comments...
BTW, this also explains why I had to add spacers between the swingarm mounting points and chainguard to stop the chain from rubbing against the guard! (the bike came without a chainguard)
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium

Offline shuswapkev

  • A's Best Friend
  • ***
  • Join Date: Jul 2012
  • Posts: 124
  • Karma: 0
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #1 on: 30.04. 2016 13:03 »
my 48 rigid with 50 a10 motor sits about 1/2-3/4 off the centre on the frame...the motor that is...think to the left..

I worried about it for a while...  then went off onto some other issue...

Offline Kickaha

  • A's Best Friend
  • ***
  • Join Date: Apr 2014
  • Posts: 117
  • Karma: 6
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #2 on: 01.05. 2016 23:04 »
The measurements I made showed that the wheel should be moved 5 mm to the right to have it centred between both legs of the swingarm.

Did you check how it was aligned compared to the front wheel before you moved it ?
1955 BSA Gold Flash
New Zealand

Online Brian

  • Wise & Enlightened
  • *
  • Join Date: May 2007
  • Posts: 1701
  • Karma: 40
  • Mt Gambier, South Australia.
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #3 on: 02.05. 2016 05:45 »
Where the wheel sits in relation to the swingarm is not important, whats matters is its alignment to the front wheel.

Firstly make sure your front wheel is centered between the forks, then make sure your rear wheel aligns with the front one.

The best way to do this is with no tyres on the rims and a decent straight edge.

Online Klaus

  • Valued Contributor
  • ****
  • Join Date: Jun 2015
  • Posts: 365
  • Karma: 10
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #4 on: 02.05. 2016 06:56 »
Hi Morris,

I have 4 SA bikes and they are all a little off.
It is importand to control the alignment from the gearboxsprocket and the rear chainwheel, this must be correkt.
As Brian said the best way to control is with no tires fit and a helping hand with a laserpointer.
May be the headstock is the critical point.

Klaus


If you think, everything is under control, you are not fast enought.

Offline duTch

  • Ricketty Rocketty Golden Flashback
  • Wise & Enlightened
  • *
  • Join Date: Oct 2011
  • Posts: 4540
  • Karma: 41
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #5 on: 02.05. 2016 08:33 »

 And in addition to all the above, is the rear axle parallel to the G'box mainshaft (which may be part of the gist of Klaus's comment). I feel this is most important.
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
Australia

Online morris

  • Wise & Enlightened
  • *
  • Join Date: Aug 2012
  • Posts: 1544
  • Karma: 23
  • Antwerp, Belgium
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #6 on: 02.05. 2016 23:00 »
To comment all of the above, I have checked wheel alignment with 2 lengths of string, and there definitely is a 4 to 5 mm misalignment between the front and the back. Also the sprockets don't line up by approx 4 to5 mm in the same sense.
All measurements point to the swingarm being out of centre.
The front swingarm tube, from edge to leg is clearly visible about 4-5 mm shorter on the left compared to the right side.
On the left, there is also no more than about 4 mm of room between the swingarm leg and the frame loop so the brake pedal spring is rubbing against it, where on the right there is a 10 - 12 mm space between swingarm and frame loop.
So if anyone got a spare swingarm lying around, I'd be glad to have it confirmed that both sides of the front tube to the leg are equal or not.
Somehow I feel a dismantle job coming up... *work*
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium

Online Klaus

  • Valued Contributor
  • ****
  • Join Date: Jun 2015
  • Posts: 365
  • Karma: 10
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #7 on: 03.05. 2016 06:12 »
Hi Morris,

what kind of SA is fit on the bike?
CD hub or the Ariel hub.


If you think, everything is under control, you are not fast enought.

Online morris

  • Wise & Enlightened
  • *
  • Join Date: Aug 2012
  • Posts: 1544
  • Karma: 23
  • Antwerp, Belgium
Re: Trying to understand what's wrong (rear wheel offset)
« Reply #8 on: 03.05. 2016 22:20 »
Hi Morris,

what kind of SA is fit on the bike?
CD hub or the Ariel hub.

Full width QD I guess?
And I know the angle of the brake arm is awkward, I really need to find another one of the right type. *red*
The grease nipple is temporarily. I ran out of straight ones
'58 BSA A 10 SA
'52 BSA A 10 Plunger
'55 MORRIS ISIS
The world looks better from a motorbike
Belgium