swingarm alignment

Hello,

I am continuing to rebuild my 1974 MKIII and was hoping to avoid rebuilding the swingarm since its "technically" a part that doesn't need servicing. However, as I've gotten everything back together I have noticed that the swingarm appears to be off centered within the frame to the point that I am concerned about the swingarm hitting/rubbing my exhaust hardware during use. Pics below show the difference in clearances between the right and left side.



A few things to note:
The bike is on its center stand in the pics
It does appear to clear the closest nut and bolt but only by the skin of my teeth
I did notice this issue before I first dismantled the bike but hoped fresh isolastics might fix it. They have not.
There is no evidence of this nut having rubbed that area of the swingarm previously.
Upon close examination, the rubber on one side of the swingarm is more supple than on the other side, so maybe someone has replaced the internals on only one side? Could this lead to an alignment issue?

I have read about reaming bushings to get the assembly to fit together but I haven't encountered much on the details of realigning an already assembled swingarm, if such a thing is possible. Any ideas on how best to proceed?

Thank you,
Anthony

Have you ruled out distortion of the SA? Easy enough to fit new SA bushings and spindle. The frame tube can wear out of round from improper lubrication of the oilite bushings (must be oiled, not greased). Look up Keigler Clamps for one method to better support the SA spindle, though not a cure for out of round tube.

Tornado said:

Have you ruled out distortion of the SA? Easy enough to fit new SA bushings and spindle. The frame tube can wear out of round from improper lubrication of the oilite bushings (must be oiled, not greased). Look up Keigler Clamps for one method to better support the SA spindle, though not a cure for out of round tube.

Click to expand...

Anything is possible. I did check for slop in the pivot when I had frame stripped down and there was none, so I'm hoping that's good indicator the swingarm pivot isn't worn or distorted. I'll look into Keigler Clamps though, thanks.

It is not uncommon for swinging arms to be twisted. Mount the swinging arm on a level table with a tube through the swinging arm bushes and then check if the axle is also parallel to the table. Mine was twisted several mm.

Yours however seems to be pushed across a little. One quick check is to drop a vertical line down from the shock mounting point on the frame to see if the mounting brackets on the swinging arm line up. This assumes the frame is correct which is not necessarily true of course.

The article the world's straightest Commando goes into detail. The rim of the front wheel should be central between the stantions. And the rear wheel rim central to the main down tube. The rear chain sprockets should align with a correctly assembled rear hub.

Get all those right and your well on the way

Please correct me if I'm wrong, but isn't the engine cradle, and thus the swinging arm, off set to one side
and this is compensated by having to offset (by about 3/16") the wheel rim on the hub to bring the centre
of the rear tyre central in the frame ?

Anvill said:

However, as I've gotten everything back together I have noticed that the swingarm appears to be off centered within the frame to the point that I am concerned about the swingarm hitting/rubbing my exhaust hardware during use. Pics below show the difference in clearances between the right and left side.

Click to expand...

That's normal. You can space the LH Z-plate out with washers (as the factory apparently did!) to gain a little more clearance if required.
(The silencers/mufflers are not Norton type and there only appears to be one rubber AV mount attaching each silencer to the mounting plate instead of two).

Staytite said:

Please correct me if I'm wrong, but isn't the engine cradle, and thus the swinging arm, off set to one side...

Click to expand...

Yes, to the left, however...

Staytite said:

and this is compensated by having to offset (by about 3/16") the wheel rim on the hub to bring the centre
of the rear tyre central in the frame ?

Click to expand...

...Not exactly, the swinging arm isn't symmetrical so the front is offset to the frame centre due to its attachment to the cradle but the rear (where the axle plates are) is not or the shocks would lean to the right as the upper mounts on the frame are not offset.

Are you checking it with anything other than the Z plate ?

L.A.B. said:

That's normal. You can space the LH Z-plate out with washers (as the factory apparently did!) to gain a little more clearance if required.

Click to expand...

Additionally you can use thin ny-lock nuts and cut down the protruding AV studs finishing with a file or Dremel to insure that the brake cable doesn't get torn up when the suspension articulates.

Best.

RoadScholar said:

...to insure that the brake cable doesn't get torn up when the suspension articulates.

Click to expand...

Only, in this instance, it's an 850 Mk3 so no brake cable.

L.A.B. said:

That's normal. You can space the LH Z-plate out with washers (as the factory apparently did!) to gain a little more clearance if required.
(The silencers/mufflers are not Norton type and there only appears to be one rubber AV mount attaching each silencer to the mounting plate instead of two).

Click to expand...

I was considering this as it would also help give a little breathing room between my left foot peg and primary cover, which are also nearly touching. I like starting simple and then working towards complicated if need be.

In regards to the mounts, my bike came with an old set of Dunstall Decibels, they actually do have two rubber mounts but they are directly in line and thus obscured in the photos.

I have looked over The Worlds Straightest Commando with interest but figured I should know what I’m starting with before I begin fiddling geometry too much. So for now I’m shooting for the world’s most unremarkably functional Commando Thanks guys.