Isolastics

Hi.
My Commando mk2a is fitted with vernier isolastics, however I have found that the rear Unit is seized.
I have slackened the large through bolt that runs to each end of the Z plates and proceeded to try to adjust the adjuster with the tommy bar and it just turns the complete unit. Has anyone tackled this job without stripping everything down with any success. I have tried the penetrating oil but access is very restricted. Next plan is to remove rear fender to give more space.
Appreciate any advice that would hopefully make it easier.
Thanks.

There should be a tiny grub screw which must be loosened first.

The kickstart side isolastic nut should be fully tight and held with a spanner while you turn the adjustable side. Try the clearance on the primary side and torque the primary side nut. Repeat until the clearance is correct. LAD has the process documented elsewhere on the forum. The alternative explanation is that the through bolt has been installed the wrong way round - the short thread should be on the kickstart side.

HoveToo said:

The kickstart side isolastic nut should be fully tight and held with a spanner while you turn the adjustable side. Try the clearance on the primary side and torque the primary side nut. Repeat until the clearance is correct. LAD has the process documented elsewhere on the forum. The alternative explanation is that the through bolt has been installed the wrong way round - the short thread should be on the kickstart side.

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I

Ok, so I read on a previous post that the grub screw needs slackened on the gearbox side of the vernier Isolastic. I take it this has to be done before the primary side adjuster is set after the desired clearance is set.

Nortoncommandoneil said:

Ok, so I read on a previous post that the grub screw needs slackened on the gearbox side of the vernier Isolastic. I take it this has to be done before the primary side adjuster is set after the desired clearance is set.

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That would be for the Hemmings type vernier adjusters (below) if that is what they are? If so, then the adjustment should be done with the through-bolt/stud fully tightened, unlike the factory or conversion kit vernier adjustment.


Edit: If factory type verniers then only the fixed abutment has a grub screw which should not be slackened (as the adjuster collar is on the opposite side). The normal position for the rear adjuster collar is on the left-hand side.

Hello. I started stripping my Commando down today to gain better access to the rear vernier isolastics. The bike is on a bike lift and supported by the frame, not on centre stand, also the primary assembly has not been removed.
What I have now is a Andover Norton rear vernier that’s corroded and seized. The mounting collar grub screw does come out if required but the complete assembly turns and I’m unable to hold the gearbox grub screw side to gain the correct adjustment, also the rubber gaiter is torn. What I would like to know is can the Isolastic be removed and what is the best method to get the mechanism either above or below the frame threaded bar fixing loop so that it can be dismantled. I have also removed the Dave Taylor head steady.
Thanks for any advice. Neil

Nortoncommandoneil said:

Hello. I started stripping my Commando down today to gain better access to the rear vernier isolastics. The bike is on a bike lift and supported by the frame, not on centre stand, also the primary assembly has not been removed.
What I have now is a Andover Norton rear vernier that’s corroded and seized. The mounting collar grub screw does come out if required but the complete assembly turns and I’m unable to hold the gearbox grub screw side to gain the correct adjustment, also the rubber gaiter is torn. What I would like to know is can the Isolastic be removed and what is the best method to get the mechanism either above or below the frame threaded bar fixing loop so that it can be dismantled. I have also removed the Dave Taylor head steady.
Thanks for any advice. Neil

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Since the entire assembly turns, you need to replace it. A properly installed AN conversion has the grub screw on the timing side and it never needs to be loosened for any reason. The rubbers are a tight enough fit that turning the entire assembly with that little tool cannot happen unless the rubbers are bad.

Depending on how much "stripping my Commando down" you're doing, will say how hard it is to change the rear isolastic. If down to just the frame and power unit, put it on it's side, remove the front isoelastic and then the rear through bolt. You can then move the frame around to where to have access to the rear isolastic easily. If not stripping that far, you can get access by rotating the power unit. If the head is off, quite easy, if not, you might have to remove the front isolastic.

I've had a couple of times with old rusty bikes where I had to hacksaw the bolt - look down a few pictures here: https://www.gregmarsh.com/MC/Norton/Norton_1974.aspx

Nortoncommandoneil said:

I started stripping my Commando down today to gain better access to the rear vernier isolastics. The bike is on a bike lift and supported by the frame, not on centre stand, also the primary assembly has not been removed.

Click to expand...

To gain sufficient access to remove the rear Iso with the cradle supported by the centre stand (850 Mk3) I removed....:
...Front Iso.
Z-plates
Head steady (Taylor)
Front lower and upper rear mudguard fittings
Battery carrier (and horn)
Removed the shocks from their lower mounts so the frame could be moved back and allowed to drop at the rear so the mudguard was resting on the tyre.

Nortoncommandoneil said:

What I have now is a Andover Norton rear vernier that’s corroded and seized. The mounting collar grub screw does come out if required but the complete assembly turns and I’m unable to hold the gearbox grub screw side to gain the correct adjustment, also the rubber gaiter is torn.

Click to expand...

Unless you can manage to free off the adjuster or unscrew the fixed abutment then it's probably a hacksaw job as suggested.

I have the rear mudguard, Z plates and battery tray now removed from the bike. From what I’ve read from your reply, I need to put the bike on the centre stand and remove the front Isolastic and rear shocker lower mounts and this should give me access to the the rear Isolastic by moving the frame back, ?
Is it acceptable to leave the primary chain case built up. ?

Thanks Neil

Nortoncommandoneil said:

Is it acceptable to leave the primary chain case built up. ?

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Yes.

Lot of work, but worth it. Pics show how I did mine a couple weeks ago.