Isolastic - part 3

Having to wait so damn long between each little bit of progress is  disheartening; I could have had this entire upgrade done in under a week if only I had control over my own time, but here we go.

☆☆☆ Adjusting front and rear Isolastic ☆☆☆ 

Whilst all Commando models can be retrofitted with the vernier upgrade, it should be noted that when it comes to adjustment there is a difference in procedure between pre-'71 and later variants: pre-'71 models have the centerstand mounted to the main frame, whereas in '71-on models it is bolted to the gearbox cradle.

When you adjust the Isolastic, you have to make sure the sub-assembly is not "under load", so if you have a pre-'71 you can support the bike on the centerstand, however if you have a '71-on you need to retract the centerstand and support the bike with a jack, on the lower main frame rails:

It's commonly mentioned that to measure the clearance of the front and rear units you should shift the engine to one side, so that all of the "gap" is on one side of the engine and you can get a more accurate reading, but I prefer to not put any stress or load on the sub-assembly, and measure the gap on both sides instead. It's probably not as accurate, but much easier to do.

The adjuster for the front Isolastic is located on the right side (starboard) of the bike; the adjuster for the rear Isolastic is located on the left side (port) of the bike. The reason for having the adjusters on opposite sides is that it helps center the sub-assembly in the frame - at least it seems so to me: when you turn the adjuster, you're essentially working against the frame so doing this from both sides (front and rear) seems like the right thing to do.

Yes, it's all a bit fiddly with the rubber gaiters, but absolutely doable; there is easy enough access to check both sides with feeler gauges, front and rear. With the through-bolt torqued to 30lbs./ft, I started from virtually no clearance on the left and on the right. To adjust the gap you slacken the through-bolt, turn the adjuster using the tommy bar that comes with the kit, re-torque and measure again. This will take a few attempts to understand how much of a turn corresponds to how much of a change in the gap; and anyway the ultimate test is riding the bike where and how you want, and noticing how it feels. Then take it from there.

In the end I settled for 0.25mm (or just under 10 thou) at the front and rear.

☆☆☆ Fixing the head steady ☆☆☆

As far as I know, the Commando was always meant to be put into production with three vernier adjustable Isolastics, but time and money constraints meant that the factory had to do the best it possibly could (I won't say "cut corners" because that's unfair), hence shims instead of the vernier adjusters, and simple rubber mountings for the head steady.

An actual Isolastic head steady became available later on, for the production racers, and was eventually manufactured and sold by the usual suspects; it has been a very common upgrade for many people, and one I would recommend.

Truth be told, I made a mistake when originally fitting the Norvil head steady years ago, in that I did not shim it at all, I just bolted everything up and left it at that. That of course was a mistake, and there was no way this could have worked properly if fitted improperly!

After all, we have the same exact one on the Interstate and it works well there, which is what made me think there must have been something wrong with mine as opposed to something wrong with the head steady's design, which is actually quite good!

So, the first thing was to remove the outer plates and clean up the rubber bushings' housing, as well as the end caps (or shim cups, whatever you wanna call them). This is when I noticed the first, glaringly obvious problem: the shim cups had not been machined properly and did not fit over the main body of the head steady; instead, they were just partly pressed on but not at all square with the outer plates, in other words there was no way this could work. I spent some time taking measurements and filing away at the shim cups until I got a proper fit, so that's one thing done.

I have new rubber bushes that I bought from Andover Norton and will probably replace these as well at some point. For now the existing ones are fine, and I also want to try making some sort of comparison between just the old and new Isolastic (meaning the front and rear mounts).

I then replaced the PTFE washers with new ones, and discovered that I had assembled the whole thing so poorly (years ago) that one of the washers was all torn to bits. Mea culpa!
After that it was "just" a matter of trying different shim thicknesses to get to a supposed ideal clearance (at the moment it's just over 10 thou). It took about four attempts, which means assembling and torquing everything each time. This is time-consuming and fiddly more than anything, but access is easy; shimming the rear Isolastic (the one above the gearbox) on the other hand must be some form of punishment in Tartarus, where Commando owners who neglect their machines are sent to shim and reassemble the whole engine-transmission-swingarm-wheel, only to find that the clearance is always wrong and having to start over, for all eternity.

As I mentioned earlier, tightening fasteners to the correct torque is very important; this is not only so the system can work as it was designed to, but also so that in between various attempts at shimming to the correct clearance, you can have a fixed point of reference when checking with feeler gauges.

☆☆☆ Test ride and verdict ☆☆☆ 

Test ride indicated expected performance of critical vehicle systems. A less dry way of saying that is "WOW this bike has never run so well!"

Time to see if all I've done is worth a damn: as I wheel the Fastback off the lift and onto the driveway, I don't hear any squeaks, rattles, clangs or any other unacceptable noises... except I can hear the rear chain rubbing against the primary chaincase ever so slightly: to be honest I don't think there's much I can do about it (without removing the chaincase again, which ain't gonna happen), so I might just wait for the chain to "find its place" after a few miles. I'll keep an eye on it.

It fires up easily enough and I take a moment to let it warm up, while checking that nothing is falling off (you never know!)

It had occurred to me that it would be prudent to check the primary and clutch at idle (with the cover off obviously), but at least from appearance it all seemed to work fine. That said, I noticed something of a wobble at the clutch that had me a bit worried at first; on closer inspection however, the clutch basket is running nice and straight and what I saw was actually the diaphragm spring slightly off-center. I could try to re-assemble it (again) to remedy this but I suspect it's not a big deal.

When you disengage the clutch with the roller needle conversion, you get this extremely satisfying little chirp, followed by a Ducati-like chatter of the clutch plates, very audible with the cover off. The point of this conversion is to give lighter clutch action, less drag, a more square lift on the diaphragm spring, but most of all it is to annoy your friends when you brag about it, which is priceless.

Engaging first gear is not as smooth as it should be, I think it's to do with the rearset linkage more than anything else, and only something I notice from idle, otherwise the gearbox is perfect as always. I can try adjusting the linkage itself but it's never going to be as refined as the original footrest/lever set up.

As I mentioned before, clutch action is light, quick and smooth, no complaints there.

The bike feels firm, taut, lean and light-footed; overall there's an immediately appreciable difference with how it was before.

There are two things I want to focus on here as I accelerate and use the gearbox along the typical twisty country lane, that is to say the Isolastic, obviously, but also how the new sprocket works: what I mean by that is whether or not the lower ratio lets me be "on the cam" sooner and longer.

Trying to separate the two things and rationally making mental notes, while the bike is running so well  and is such ridiculous fun is actually difficult and a bit strange, and also the point is that it all works together to deliver such a fantastic ride, that that's the indicator I should really be focusing on!

So, as strictly related to the new gearbox sprocket, comparing it with the previous 21-tooth item, this now feels "quicker" for lack of a better term, and it definitely unlocks the 4s camshaft much sooner and much more easily than before. Exiting a corner I twist the throttle as I normally do, but now acceleration is definitely different, and it has changed to be a little bit nasty; I think to myself "hey... where did you come from?" as the needle on the rev counter hits 5.000 and the bike rights itself with a little flick of the front end, then levels out pointing straight at the following corner.

Moving on to perceptible vibration through the rev-range, I am relieved and enthusiastic to report that the Isolastic upgrade works.

I'm in second gear approaching an indicated 2.800 rpm when suddenly, there it is, the magic switch: there is no change whatsoever in the exhaust note, no drop in acceleration or upset in handling. Rather, the very physical perception of vibration disappears and is replaced by a sensation of riding on air, as Peter Inchley said:

The Commando is smooth as a magic carpet and just as fast.

I wonder what the Norton development team must have felt like when they tested the Commando for the first time and were the first to experience the Isolastic; that must have been a good day at the office, for sure.

Just thinking about the handling now, it is so smooth, there is a familiar feeling of unending torque and constant acceleration, but finally unmarred by vibration; the term "GlideRide" immediately comes to mind. Power delivery is now absolutely effortless as the machine glides over the road enveloped by a soundtrack that is equally smooth and full-bodied. Wow, wow, wow, what a bike!!

"Suddenly we've started a revolution on two wheels - It's called the COMMANDO 750. Inclined engine, better cooling. GlideRide frame—goodbye vibration" - Motor Cycle News 1968

Since 2013 I have been much more involved in the maintenance of this motorcycle, personally taking care of most tasks except for those that require specialist equipment or skill beyond my own (e.g. when I sent the cylinder head to SRM to be refurbished). Since then, I have gradually and significantly improved the Fastback's overall performance: you mustn't take this to mean solely speed, but also reliability, ease of use, handling and things of this nature.

Already a couple of years ago, I got it to the point where the bike was very much in a sweet spot, and have continued to improve it with things like a clutch overhaul, different tires, new exhaust silencers, etc.

Every step has brought me closer to that WOW moment I mentioned above, and now with the 20-tooth sprocket, and with the upgraded and properly adjusted Isolastic, this motorcycle is an absolute dream to ride.

Simply put, the Fastback has never run so well in the fourteen years I've owned it; I couldn't be happier.

This process of constant improvement, with discernible steps and stages, closely mirrors the path of liberation from karmic matter as understood in Jainism. It's obviously an oversimplification, but the moment I decided I was going to take over the maintenance can be equated to the point where one stops the influence of karma, with every subsequent improvement as a way to gradually shed said karma until the attainment of Moksha, i.e. a properly sorted out motorcycle.

Once you've wrapped your head around that we'll then expand on what motorcycles actually are... but I'll leave that for another day.

The little snippet below from a now old copy of Classic Bike sums up perfectly what this motorcycle feels like to ride:

Test complete.

☆☆☆ Assorted musings ☆☆☆

The workshop manual specifies an ideal clearance of between 0.006″ (0.15mm) and 0.010″ (0.25mm) but there is something to be said for a "trial and error" approach, especially after a rebuild. Just as for clutch stack height, in the end what works best for you may not be exactly what is specified in the manual. I may well end up revisiting the adjustment on mine after I've had a chance to take it on a proper ride.

Check the clearance by placing the feeler gauge between the PTFE washer and the shim cup.

Set the clearance for the front and rear units first, then move on to the head steady.

At the moment I'm at about 0.010″ front and rear, and just over 0.010″ for the head steady. This seems mostly just right, but I think I noticed some vibration creeping in around the 5.000rpm mark during the test ride, so I may try some further adjustment to see if I can iron this out.

Besides from setting the correct clearance (whether it be with shims or vernier adjusters) another thing that is very important is the torque setting for the various retaining bolts. You must get this right, or the whole system just isn't going to work. Also, checking and adjusting as needed may be something to add to a yearly service.

Torque the Isolastic locknuts to 4.15Kg-m (30lbs./ft) for the front and rear units, and to 3.4Kg-m (25lbs./ft) for the head steady.

If clearances and torque settings are all correct but the Isolastic still won't kick in when the engine is around 2.500/3.000 rpm, check for something in the rubber mounted sub-assembly (engine-gearbox-swingarm-wheel) touching something not rubber mounted (e.g. main frame, Z-plates, side stand).

Related to the point above, you should always keep in mind that, when fitted on a Commando, rearsets introduce a problem that's hard to circumvent: the gearshift linkage effectively connects the mainframe to the sub-assembly, but without any sort of rubber mounting, cushioning or other flexibility built in. This creates a point where vibration is transmitted and can negatively affect the effectiveness of the Isolastic.
By contrast, the original set up has the gear lever bolted exclusively to the gearbox, while the footrest is bolted to the Z-plate and there is nothing connecting the two, other than your right foot.

Seeing as I run a belt drive conversion, is this now a beltcase rather than a chaincase? Ah, the laughter.

You may have noticed in some of the photos that bits of the frame look like they could use a touch-up or even a full on paint strip and re-spray. I want to address the lower yoke, which is not looking good, but other than that I'll leave things as they are and the reason for that is that 'done' is better than 'perfect'.

An Aladdin blue flame kerosene heater is of course the only appropriate means of heating the shed when working on a British motorcycle (a cast iron wood-burning stove would otherwise be acceptable for a Harley-Davidson or other machines).