Swing Arm Clearance Issues

My 1972 Commando had big bore headers and Dunstall pipes on it when I bought it. It looked okay, but I decided I wanted the stock look and sound. I am in the middle of installing stock headers and stock silencers. These were on another Commando I have and fit that bike fine.

But on this bike, there is inadequate clearance between the left side of the swingarm and the inside nuts for the rubber exhaust mounts. If I bounce on the rear of the bike, the top inside nut for the rubber mount jams into the swingarm. I wonder what might cause this? It is as if the Zplate is not straight. Or the swing arm not centered. Or??

The bike is very nice, straight, and had a ton of money spent on it by the previous owner at a British restoration specialist. It does not appear to be bodged.

I know I can put the large exhaust mounting plate in a vise and bend it, and probably cure the problem. But I just made it to stock specs, out of stainless, and am reluctant to mangle it. Suggestions please.

Stephen Hill
Victoria, BC

I had similar fouling on R side of a '72 by the stud sticking beyond the nut so trimmed that to get ~1/4" gap but yours sounds closer yet if its fouling the nut. You got your self a real mystery and maybe opportunity to reveal innate differences in Cdo's. I'd sure be restless till I measured each bike to see where they differ and clue to what's going on. DPO may have tweaked mounts to allow the Dunstall set up to install.

First shorten the rubber mount studs, nearly always too long. Second (should be first really) check the correct longer two spacers are in place between frame tabs and Z plates. They should be wider than the main ISO spacers. Norton made these so the Z plates kicked out at the back, a true bodge. If you need to you can add washers to these, just thick enough to get clearance.

Oh yeah Kieth, thanx I'd forget about the Zplate spacer fudging to be aware of as true to factory form.

Thanks Keith,

Is it a big deal to remove the left zplate? Is it possible to remove the left hand Zplate without screwing up the rear isolastic adjustments?

So once it is off I then measure the rear spacers and make sure they are lightly longer than the main spacer on the isolastics. Makes me wonder how the rear spacers could be too short. From factory? Somebody used the wrong ones?

I like the idea of shimming the Zplate better than bending it or the mounting bracket.

Stephen Hill
Victoria, BC

You won't mess up the isolastics by loosening or removing that 1/2" nut. Just make sure you re-torque it back on. The adjustments are internal. The nut holds it all together.

Dave
69S

...check the correct longer two spacers are in place between frame tabs and Z plates. ......

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Longer two spacers? The parts book show 4 spacers of P/N 060471. What is the P/N on these longer spacers?

Keith1069 said:

First shorten the rubber mount studs, nearly always too long. Second (should be first really) check the correct longer two spacers are in place between frame tabs and Z plates. They should be wider than the main ISO spacers. Norton made these so the Z plates kicked out at the back, a true bodge. If you need to you can add washers to these, just thick enough to get clearance.

Click to expand...

Hmm, new one on me. Mine are all the same length.

Just finished the install of the stock pipes and silencers. The interference problem on the left side is solved. I undid the large nut and two bolts that hold the z plate on to the frame. Added two .060 washers (one for each bolt) in behind the z plate at the rear, which converts into about .125 plus extra clearance back at the swing arm. Then I ground back the mounting stud for the exhaust rubber, got rid of the flat washer, and used a low profile nut. I gained about .250 in total.

Stephen Hill
Victoria, BC

They say these commandos are really just the basic kits you must finish on your own. Just be glad its not the horn fouling.

Hmm, new one on me. Mine are all the same length.

Click to expand...

On most I've worked on and mine the fronts (ISO) are 1/2" wide and the rears or rather top rear and lower are 5/8".

I think I can explain the apparent confusion re: the length of the front and rear spacers. The front spacer (on the iso stud behind the z plate) does appear to be shorter in length than the rear spacers. The battery box mounting tab on the front takes up about .125 of an inch. With the rear spacers longer, this is intended to should keep the z plates parallel to the brackets mounted to the frame. In my case, there just doesn't leave enough clearance for the swingarm. I can see where the swingarm was chewed from before it was powdercoated in the recent frameoff restoration. In other words, it has always been an issue on this bike. I haven't started the bike yet, but am looking forwards to the Norton exhaust rumble, instead of the Dunstall blat.

Stephen Hill
Victoria, BC

The Iso one is about .55", the other 2 are .625", this creates .625" gap from frame to plate on all 3.
Which means mine are not all the same, but the gap is. Clears the swinging arm alright.
Best suck it & see, it is easy to remove the plates.