Isolastic

Rivers of ink have flowed for half a century (not to mention the countless bytes within the virtual world) to describe the Norton Commando and its revolutionary Isolastic system, arguably mankind's greatest achievement of all time.
I would hazard that any article written about this bike mentions it at least in passing, often flirting dangerously with plagiarism of what's come before...

So, since you already know all there is to know about the Isolastic, I will instead tell you about my machine.

As you may know, I got this bike as a... well, the word that actually best describes the state it was in, is the French épave.

The restoration effort we undertook was very thorough and not without its hurdles, however the result was well worth it. At some point with these endeavors you can reasonably claim to be finished with the restoration, and begin actually using the damn thing in the real world.

This is where we enter a much more subtle realm, that of maintenance and improvement: since the whole thing actually works, it becomes easier to isolate (no pun intended) those areas that can be improved, and it's usually possible to be far more surgical and focused. This is where my motorcycle has been for a good while now, and whenever I do bring it in for maintenance, it is for very specific and relatively easy things.

There is a vast repository of knowledge available when it comes to the Norton Commando, and most problems have already been encountered and solved by someone else, so you're hardly ever in uncharted territory.

Of all the things that have been said of the Isolastic, in my opinion two in particular really capture the feeling of a properly set up system: it has been described as a "magic switch" (source unknown, but a common enough idiom among Commando owners) and as "floating drive" in Cycle magazine's September 1969 test of the 750 'S'.

There is a point in the rev range, usually when hitting 3.000rpm, where all perceptible vibration simply vanishes. What's important is that this is not a progressive, gradual thing; it is a sudden (but predictable) on/off magic switch, unmistakable and impossible to ignore, it just never goes unnoticed by the rider. The next thing you immediately realize is that no other motorcycle in the world behaves this way, and by the time you're done thinking that, you're usually tearing through the gears and accelerating hard, surfing a tidal wave of torque and horsepower that is, in a word, addictive.

That surge is entirely down to the Isolastic being in perfect shape, otherwise the ride will be mediocre at best, and downright dangerous if not addressed quickly.

During my rebuild I decided to fit the vernier upgrade, as I didn't want to faff around with shims, especially for the rear unit which is harder to service. It seemed like a good idea at the time...

What I didn't know, was that the kit I ended up fitting was a poorly made reproduction using a very hard rubber compound, and just bad engineering at its core. Repeated attempts at setting the right clearance never seemed to produce much of a difference, and I feel it is now time to get back in there and sort this out once and for all.

☆☆☆ Disassembly ☆☆☆

The first thing to do is to study the original Norton Workshop Manual thoroughly, and then peruse the excellent accessnorton forum if there's anything that's not quite clear.

Overhauling the Isolastic (plus a little extra, bonus task while you're at it - more on that soon) is a fairly big job in terms of the amount of stuff that needs to come off the machine; you also need a couple of special tools and pullers, possibly an air/impact wrench or a very long breaker bar.
That said, it is absolutely doable for the home mechanic.

Let's get started!

Because the Commando is essentially made up of the main frame and the powertrain sub-assembly, you need to support both independently at different times. You can do this with a jack underneath the lower cradle tubes of the main frame, and the centerstand which is bolted to the gearbox cradle on '71-on machines. You may need another jack to support the front of the crankcase when the front Isolastic mount is removed.

The primary drive has to come off, no point dancing around this. Get stuck in there and remove the crankshaft nut, remove the stator and rotor, then dismantle the clutch and pull the whole basket off.

Yes, it's a wee little breaker bar and it worked a treat. After all, as Archimedes famously said "Give me a lever and a place to stand and I shall remove the crankshaft nut."

The tinfoil was a precaution in case there was any oil, but since none seemed to have seeped past the crankshaft seal, I will use it to make a hat, as the one I'm currently wearing is a bit tattered.

Needless to say, keep all the parts neatly stored in clean containers, don't lose anything and pay attention to woodruff keys and various shims and spacers throughout. I won't get too specific here because if you're thinking of doing this on your Commando you really need to read the workshop manual.

Once the alternator and the actual primary drive have been removed, all that's left is the three retaining bolts around the crankshaft: these are threaded directly into the crankcase, so take a moment to control your breathing, visualize the parts moving as you undo them, and treat everything with respect. Gentle hands, ok?

And that's it, that's the primary chaincase removed, easy, right? Actually, provided you have all the tools available and you know what you're doing, getting to this point is lightning quick; LIGHTNING QUICK, you guys.

Some of these parts look a bit dirty, I'm going to give everything a thorough clean and it's going to look like new in here when it's all back together.

If removing the primary drive is a relative breeze, what follows is a descent into madness, as you remove more and more parts from the motorcycle (gas tank, complete exhaust system, at least one Z-plate and both side panels) and a balancing act worthy of a Chinese acrobat as you lift and move the powertrain and the frame, then the frame and the powertain, up and down, back and forth, sideways and oh crap it's gonna fall! Have someone there to help you. Thank you dad.

We can now remove the front engine mount. You'll also note that the head steady and the air filter will come off to gain some wiggle room.

There's nothing else left to remove around here, so it's time to stop procrastinating, bite the bullet and get stuck in with the rear mount.

The rear Isolastic housing is now visible but still not fully accessible, so we have to either lower the sub-assembly in the main frame, or lift the main frame off the sub-assembly. Oh, and the rear shock absorbers may need to come off for this part, just to keep things interesting.

Once the old Isolastic rubbers are removed by whichever method you see fit, it's important to clean the housings and use a lubricant that will not damage the rubbers: this is crucial or your nifty new kit will perish within a short time and you'll have to start all over.

In my case I first lifted the front engine mount out of place (not without difficulty I must add) and clamped it in a soft jaw vice, then bashed the crap out of it to get the old kit out.

For the rear, since the gearbox cradle stays where it is, I rigged up a puller using part of the clutch tool and some bits of rubber to protect the frame. Surprisingly, it worked well:

☆☆☆ Defects of my kit - comparison with Andover Norton parts ☆☆☆ 

I now want to bring your attention (if you're still reading, that is) to a comparison between the badly made kit and the proper new one by Andover Norton.

You can see that the old kit's metal tubes are far too big for the bolts, and only held by two abutment pieces, but only one at the front/left and one at the rear/right... not even one on each side for each mount! Supposedly, the torque setting would bring the whole thing in alignment and somehow work... This is just complete lunacy and it clearly cannot work.

To confirm my suspicion, I then found this: https://www.accessnorton.com/NortonCommando/isolastic-conversion-kit.5053/

The metal tube itself is shocking, it's a crappy seamed pipe that I wouldn't use for a toilet roll hanger.

By contrast, the one in the Andover Norton kit is fully machined and a proper fit for the retaining bolt:

Another glaring difference, and perhaps the most important, is the hardness of the rubber compound:
The inferior quality kit is definitely harder and even the shape of the rubber bushes, and the overall finish is just off.
Andover Norton's is soft and squishy at the front, a little firmer at the rear.

☆☆☆ Reassembly  ☆☆☆

I started by fitting the new rear unit, it is obviously a tight fit and you have to compress the rubber to get it started, but with careful use of a flat blade screwdriver, it is possible to guide the first bush into place (this is where some grease is also essential):

Once in place, the end caps, PTFE washers and rubber gaiters go on:

Getting the front Isolastic in the housing is a lot easier:

After installation, it's just a matter of lowering the main frame on the powertrain and bolting them together using just three bolts: front, rear, and head. Although the image below is very familiar to Commando owners, when you see this in the flesh metal it's really striking, to see that this motorcycle has been engineered and built like this, a very gutsy move by the Norton team, and one that will never cease to impress me, and that I'll never cease to praise:

Before bolting too much stuff back on, this is a rare opportunity to give this bike a deep clean, something dad did using a compressor-assisted sprayer with kerosene/gasoline. It's essentially one spark away from being a flamethrower, ok?

The next phase will be refitting the primary drive, actually adjusting the Isolastic, then refitting exhausts and bodywork; that may have to wait until February (!) but this post will surely keep you busy until then...