NORTON COMMANDO REBUILD
Martin Peacock had a vision, a conversion on the road to Bude. He understood that he wanted a Commando, and this is how he made it…
Martin Peacock had a vision, a conversion on the road to Bude. He understood that he wanted a Commando, and this is how he made it… Part 4: Braking Strain
With Spring very much in the air, my project was picking up some pace. Warmer weather, longer days and my shorter, flexible working hours made for more shed time. I invested some of this on riding my Triumph to a classic vehicle show in Corbridge. This was 50 or so miles of very pleasant riding up through the Northumbrian countryside. The bike thrummed along with its usual even beat and I reflected that the Norton would do well to match the Triumph’s reliability.
Corbridge, on the River Tyne, was an excellent setting for the show, which featured a sunny day, live music and a Norton Owners Club stand. As I had hoped, there were several Commandos on show so I could chat with the owners and get some pictures showing assembly details such as control cable routing. A couple of the bikes were Mk3 Interstate models; one was a real gem having covered 250,000 miles with its original owner.
Meeting another RealExpert named Richard was a considerable bonus. Richard Johnson races classic Nortons and provides engine repair services through his business, ‘ Top End Engineering’. I had already found a pair of +40 NOS pistons on eBay, probably the only real bargain of the entire project, but I needed to get the barrel rebored. Richard, in Morpeth, wasn’t exactly local but was near enough and he was happy to take on the work on my barrel and head. This, I thought, just needed new valve guides and the seats recut, but as we will see later, there was a serious problem lurking there. As luck would have it, he was racing at Croft Circuit, only a few miles from my house, on the following weekend so he could collect my head and barrel.
Braking bad
Removing the pushrod assembly from the rear brake master cylinder took three days of soaking in Plus Gas. The mounting body, piston and reservoir were useable, but I needed a new cylinder and pushrod as well as the overhaul kit of seals.
Persistence, patience and penetrating oil, together with the right peg tool and a lot of
heat were needed to remove the front caliper blanking plug. The outer piston came out fairly easily thanks to access from both sides. The inner piston was another matter, with there being no means of drawing it out. The answer was, if not obvious, logical. I couldn’t apply pressure with brake fluid, even if the caliper seals were up to it, but I did have a grease gun.
Whether by accident or design, a grease nipple was a straight swap for the bleed nipple. The other piston served to confine the grease to the inner half of the caliper, so it had no escape route other than by pushing the inner piston out. It worked like a dream, some steady pumping of the grease gun soon had the piston poking out of its bore. The same trick worked for the rear caliper, so I put the parts on order, including pistons with threaded extraction bosses to simplify removal. My next task was to dismantle the front wheel. Wheel classic Lacking the complication of a drum brake, the front hub is a simple bobbin holding two bearings. I polished it, replaced the bearings and sent it to Central Wheel Components for rebuilding with a new stainless steel rim and spokes. The timing was such that I could pick up the finished wheel at the April Stafford show.
Although removing the rear tyre and rim was about as easy as these things get, dismantling the hub itself was resolutely opposed by the bearing retaining ring. I had bought the correct tool, a remarkably expensive peg spanner, but that broke at the first sign of resistance. Fortunately, I was able to repair it for use on the replacement retaining ring.
It took brute force with a hammer and punch to remove the retaining ring flange, this needed replacing no matter what by this stage. I could then remove the cush drive and expose the central boss so I could apply heat directly around the retaining ring. I then drilled and tapped three holes in the retaining ring body and screwed on a length of ¼” flat bar. This, plenty of heat and the realisation that it was not, as the manual claimed, a left-hand thread, finally allowed me to unscrew the blighter.
Now it was time for polishing again, one of my least favourite tasks, even if the transformation from scabby lump to a thing of beauty is rewarding. The rear hub was first up so I could take it to the Stafford Show and drop it off when I collected the rebuilt front wheel.
Restoring the calipers to their past glory took much time and effort, starting with coarse abrasive polish to remove the major dings and scratches. This effort was against the mild headwind of advice from our esteemed editor insisting that a modern, twin disc set-up was really what I wanted.
No doubt he is right, but I rather liked the ‘Norton Lockheed’ calipers and wanted to at least give them the chance to show their stuff.
My polishing work continued to the Z plates, inner chaincase, footrest mounting spacers and clutch lever. This done, I put them aside for later assembly after fitting new seals and the alternator grommet to the chaincase. I also painted the front mudguard bridge, rear saddle clamp and seat clamping lugs. Later I cleaned up the brake discs that, apart from surface rust, were in good condition. The centres came up nicely with a couple of coats of high temperature silver paint.
The rechromed parts had arrived well before I was ready to use them, so I had accumulated quite a few refinished parts ready for assembly, including the wheels with their sparkling rims and spokes. Thankful for getting away from polishing and painting, I fitted the front mudguard and its new mud flap, chrome lower brake hose bracket and new grabrail.
Turning to the rear hub, I refitted the cush drive with the original inserts as they were in good order. This needed a great deal of levering, lubrication and other mechanical persuasion to get the not so squishy rubber buffers back into their burrows. I was very relieved to tighten the new retaining ring over the cush drive spider and close the chapter on the rear hub.
My preferred method for fitting tyres is to hand over a modest amount of cash to a local mechanic who has the equipment and experience to make light of it. I had retained the oddly out of place brand new tyres fitted to the bike but supplied new tubes. With these and the brake discs fitted, I put the wheels back on and completed the transformation of the growing assemblage of parts into something like a motorbike. Before
going any further, I set up the Isolastic mount clearance and quickly learned that, ‘Vernier’ adjustment or not, it was tricky to get right. I then bolted on the rear light assembly and attached the Z plates and left footrest hanger before getting back to the brakes. Slowing down
The Commando was my first bike with discs but it was going to take a quite a bit of cash and no small amount of effort to turn them into brakes. The rear brake needed most of the master cylinder replacing as well as the short pipe to the caliper and, as I found later, the pressure switch. Both calipers needed new pistons, blanking plates, pads and seals.
Technical notes from RGM and Old Britts were very helpful with assembly of the rear master cylinder. The rear brake is identical to the front, even though the weight transfer during braking means less braking power is needed. There is, therefore, a very real danger of locking the rear wheel, especially on a wet road. Norton dealt with this by putting an adjustable stop on the master cylinder actuator rod to limit its travel and thereby the pressure applied to the pads. Although the Workshop Manual is helpful insofar as instructing you not to disturb this adjustment, it falls short when it comes to setting up a new actuator, and this is where third party sources are so useful.
I mounted my all but new rear master cylinder on the right footrest hanger with the brake pedal, and attached the assembly to the right Z plate. Pausing only to fit the kickstart, I assembled the calipers with their new parts and seals. I had chosen higher performing Ferodo Platinum series pads for the front caliper and, bearing in mind the previous paragraph, standard pads for the rear.
Not only did my bike not have its front master cylinder, the significance of which I had seriously underestimated, it also lacked the parts between it and the caliper. Looking at the parts diagram, I found that a Commando’s front brake piping comprised: a hose from the master cylinder to the top yoke bracket; a pipe from the top yoke to the bottom yoke; a hose from the bottom yoke to the fork slider bracket and, finally, a pipe from there to the caliper. My philosophy for hydraulics is much the same as it is for electrical wiring. The fewer connections the better. There just had to be a simpler way of doing this.
As for the master cylinder, I found many suggestions online for using and adapting master cylinders from numerous modern bikes. What I wanted though, was one that would fit on the back of the original switch cluster. Andover Norton had an improved type with 13mm bore, but at a price that encouraged further research. When I did decide that it was probably the best option, it was no longer available. Naturally, they introduced a new and better version of the original after I had completed the rebuild.
Eventually I noticed that the Triumph T140 range used the same switch cluster so the Triumph master cylinder should fit. It did, and I found later that it was the same as the one on the Westworth Commando but I had failed to notice. All I needed now was a braided flexible hose running from the master cylinder to the left fork slider bracket,
the short pipe from there to the caliper and a pressure switch for the brake light.
The original pressure switch attached directly to the master cylinder. This was not an option now but Venhill supplied a neat banjo bolt, incorporating a pressure switch, for attaching the hose to the master cylinder. Ordering a custom brake hose was simplified by the hose builder feature of the HEL website. This allows you to specify every aspect, including the end fittings, angle of the fittings, length, supports and even the colour.
Stig’s Fasteners supplied a set of 1½” 1032 UNF screws to secure the new master cylinder to the switch. I then fitted the new brake hose and attached its support attached to the lower yoke with a small bracket. Then, and with some difficulty, I fitted the short pipe to the caliper. So far so good, I just needed to add brake fluid to check for leakage and bleed the system.
Drum brakes and Bowden cables gained increasing appeal as I struggled to get the pipe connection to the caliper to seal. Looking more closely, I could see the thread and seat in the caliper were damaged. I cleaned up the thread and lapped the seat in with fine grinding paste and the flared end of an old brake line. I also filed down the lower threads of the brake pipe nut to prevent them from binding when the nut was fully home. This finally solved the problem so I could bleed the brake and have no leakage under pressure. The rear caliper needed some fettling too but it held pressure and I now had two working brakes, including their pressure switches.
Next I fitted the sidestand and right footrest, before getting the bike off the lift and back on to its own two wheels so I could push it out into the sunshine. I put the seat on and sat on it, resisted the temptation to make ‘brrm brrm’ noises, adjusted the levers and tightened the handlebars. But there was a nagging problem. The ground was too far down for comfort, even allowing for more weight to be piled on as the rebuild progressed. I checked the length of the rear suspension units against the specification and found they were a little too long. Swapping them for a pair 10mm shorter than standard proved no problem and was enough for me to put both feet flat on the ground.
One reason I had taken the bike off the lift was to carry out some maintenance. The Eazy Riszer bike lift is a simple and effective device that uses a lead screw to raise and lower a lifting frame on a rectangular section, vertical guide. Mine was sticking as I lowered it, resulting in occasional sudden drops of the bike accompanied by a terrifying clonk and much shaking as it settled down again. Cleaning and waxing the support column and lubricating the lead screw restored the normal smooth operation.
My other reason for getting the bike down was to turn it around so I had better access to
the left side and primary drive. I tightened the front wheel spindle pinch bolt and the rear light bracket just to warm up. Then fitted the speedo cable and cleaned and repainted the pillion footrests before turning to the primary drive.
Fitting the inner chaincase, with a new gasket for the crankcase jointing face, was straightforward other than the need to adjust the steady that holds the chaincase centre. This is attached to the left engine mount and has a backing nut so the chaincase is held in its neutral position without being pulled in towards the engine mount or pushed away from it.
A key feature and selling point of the Mk3 Commando was its electric start. Mine
only had the motor idler gear and a nonfunctional solenoid when I bought it. Now it had the electrical side sorted but none of the whirring around bits. I decided to defer both the cost of over £1000 for parts and the added complexity until I had the bike on the road and sorted. This left me to fit the engine sprocket and clutch with the triplex primary chain, chain tensioner, alternator rotor and the stator on its fancy alloy outrigger. This was required to clear the currently absent starter drive gear although the original spacer was retained so the rotor could be fully tightened.
The resin encapsulation around the new stator windings was too close around the mounting holes and needed trimming back so the nuts could be tightened down properly. This was a 180W three-phase type matched to the new solid state regulator. Although the maximum output is the same as for the original single phase, RM-23, the three-phase alternator produces more power at the lower engine speeds associated with classic bike riding.
All I had to do now was tighten the clutch retaining nut and fit the plates and diaphragm spring – having already checked the plate stack height. It was low by about 1mm, probably because of the two nonstandard composition plates, but I decided to try the original set. Firstly though, I locked the back wheel, easier with a working brake, engaged a high gear, then tightened the clutch nut, aiming for its specified 70lb.ft. The nut tightened initially, but the torque reading did not increase as I continued to tighten. Something was seriously amiss, but by the time I realised it, the damage was done.
The clutch hub is located on the mainshaft by a small circlip seated in a groove on the shaft. This didn’t seem enough to withstand the force of a fully tightened clutch hub, but it was the right part, in the right place. It definitely should not have failed as I tightened the nut, jamming itself in the clutch location spacer, but it did. As if that were not enough, the transfer of axial force to the mainshaft appeared to have pulled it out enough to lock up the gearbox, although a moment’s thought said that was impossible. Whatever the cause, there was nothing else for it than to walk away muttering some of the more explicit shed incantations as Mr. Cockup, having waited so patiently for so long, chuckled quietly in the background...