NORTON COMMANDO Mk3 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...
Iblame that chap Westworth for this. Even though Norton’s Commando has impressed me since seeing a shiny green Fastback pop an unexpected wheelie in the late 60s, I couldn’t see myself owning one. Just a little too much bike to handle and a reputation for trouble. No, my excellent 650 Triumph will do just fine thank you very much. At least that was my thinking until I saw Frank’s immaculate Mk3, Electric Start 850 gleaming in the Cornish sunshine.
It looked gorgeous. Say what you like about the Commando, they really got that part right, and there’s no harm in looking, is there? My mistake was to take up the offer of a ride, a slippery slope if ever there was one. Starting on the button, then a brisk run around the local lanes left me smitten by the strong engine, comfort, easy handling, real brakes and, well the whole package.
Smitten or not, I was aware of the ups and downs of owning a bike waggishly but not inaccurately described as: ‘a brilliant but deeply flawed motorcycle.’ This had less to do with bad design than senior management being more concerned with inter-company rivalries and settling old scores than making a world beating motorcycle. Norton’s engineers knew what was needed but had limited scope to implement changes. This sad tale is related by Steve Wilson in his book: ‘Norton Motor Cycles from 1950 to 1986’. Tony Page in RC71 defined his Commando as the ultimate classic bike: ‘...it has to do everything well and be the bike that I lust after while gazing at it in the sunshine or rain despite already owning it.’ Or as the Frank himself puts it in RC76: ‘Some motorcycles just make a chap want to ride. To forget the day to day nonsense of earning a living, feeding the cat and so forth. This Commando is one of them.’
Yes, there is no shortage of praise and with upgraded parts it can be a magnificent machine or, with less able or neglected
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…
spanner work, a nightmare Nonetheless, most Commando riders love their bikes – including the owner of a Mk3 Interstate I met. He was still riding his some 40 years and over 250,000 miles since buying it new. This appeal goes far beyond reason: if the Bonneville is a 60s icon then the Commando is surely its younger mistress; and a high maintenance one at that.
I could hardly resist and started looking out for a decent Mk3. This was the final development, not just of the Commando but also Bert Hopwood’s hastily penned 1948 design for a mild mannered 500cc twin. Now a rasping 828cc, paired with a gearbox designed in 1953, it was a testimony to Norton’s cash strapped engineers that they produced such fine performing machines well into the 70s.
By this time, the Commando had put on weight, tipping the scales at around 430lb (196kg). Though lighter than 500lb contemporaries like the T160, it had no more power than the svelte 750s. What it and the earlier 850s had, however, was stump pulling mid-range torque from a low revving engine designed to overcome the damaging high piston speeds and bottom end flexure of the 750 Combat engine. Still no slouch but more cruiser than superbike, the Mk3 was introduced with around 140 changes from the previous model. These were to improve reliability, meet tougher US regulations and compete with the latest Japanese offerings:
Electric start, marginally effective but it can work well with upgraded parts New switchgear Rear disc brake Left foot gear change Hydraulic primary chain tensioner Large but restrictive airbox to reduce noise Improved, sprung head steady Hinged seat Anti-sumping valve and screwed plug for timing chain checks Strengthened crankcases with larger diameter crankcase bolts and shot peened conrods ‘Vernier’ Isolastic mounts (adjustment by a threaded end cap instead of shims)
Eventually I spotted a recent USA import that seemed a good prospect for my very own ultimate classic bike. It was described with more enthusiasm than accuracy but on the face of it there wasn’t anything major needed to get it up to scratch. The timing and location were convenient for the Stafford Show so I arranged to see it. The trouble was that I didn’t know what I was looking for and didn’t have someone who did with me. Such foolishness has a price and I overlooked many important points such as the missing front master cylinder. Yes, I spotted it was missing but did not know that a replacement was practically unobtainable. Other missing parts were the electric start including the entire
starter train, side panel, coils, coil bracket and oil separator for the oil tank breather.
Later I found that some of the parts still attached were from early models, such as the 750-type head steady, carburettors and manifold stubs. These were the early 30mm types not the correct 32mm. Richard Negus spotted that and more from 120 miles away from a picture I sent of the newly rebuilt bike, but I had missed that little detail completely. On the plus side, it turned over, had good compression, all four gears and had no signs of accident damage. Strangely, it had brand new tyres and plugs. No coils, contact breakers, battery, ignition wiring or key and only one HT lead, but new plugs. As an American might say: ‘Go figure!’ At least the starter solenoid was there, but it didn’t work. I wonder what he meant by: ‘All electrics are correct and in good order.’
Of course I bought it! My offer was clearly not low enough, such was the eagerness of its acceptance. Still, even at the price paid, a budget of £3k - £4k would put me in the right bracket for a good Mk3, wouldn’t it? Pause here for a wry smile…
Let’s talk about that, budgeting for recommissioning, restoration, rebuilding – call it what you will. There is the essential stuff: missing parts, worn out or corroded parts, seals, gaskets, fasteners, tools and so forth. Much trickier though are decisions about replacing functional but corroded fasteners, refinishing chromed and painted parts and fitting new, upgraded parts for improved reliability and longevity. Examples are electronic ignition (a no-brainer in the absence of coils and contact breakers); a chill cast camshaft replacing the still serviceable but generally short lived case-hardened original, 3-phase alternator with solid state regulator and heavy duty AGM battery.
All very sensible, but that was £525 out of the budget. Add a surprising £310 for mostly stainless nuts, bolts, screws and washers; £750 for painting, chrome plating and powder coating; £100 for special tools, £190 if you count the vacuum gauges and optical tachometer for setting up the carburettors and clocks. Don’t discount postage charges either with VAT on top: that lot came to a whopping £440. That’s over £2000 before costs for the engine work, suspension, gearbox, primary drive, Isolastic mounts, electrics, carburettors, brakes, wheels and, well, everything else. I put off buying the electric start components, especially the upgraded motor, as they are in a league of their own, but most parts are not all that costly. It’s just that there are an awful lot of them.
I estimated that there are over 2100 parts that must fit and work together. By the time I’d finished, each and every one had been replaced, repaired, refurbished or refinished – right down to the spokes. This is the advantage of ignorance, you can get on with a worthwhile project that you wouldn’t touch if you knew more up front.
Meanwhile, back in the shed with the sorry looking Commando, it was time to get organised. A bit late I know but I started with reading through the workshop manual and NOC Service Notes to get an idea for how it should be put together and, indeed, taken apart. By now there was no doubt about that and, not to push the mistress analogy too far, this called for a complete strip down.
The petrol tank was easy, with its severed fuel lines and just a bungee cord holding it on. The seat simply lifted off after slackening the knurled knobs – so much for the Mk3’s hinged seat! My bike lift and a couple of extra hands for the pushrods made removing the head much easier – apart from dealing with the near inaccessible inboard carburettor Allen screws.
This revealed standard, shiny topped pistons and bores that looked recently honed. The head wasn’t so good, with the left combustion chamber oily and black with carbon deposits. One valve guide was broken and, as I found later, that wasn’t the worst of it… but at least it was the right head, although probably not the original. Removing the barrel confirmed the pistons were original Hepolite and the conrods, camshaft and flywheels looked to be in good condition.
Removing the primary chaincase was straightforward, although I was surprised to drain over two litres of clean engine oil before removing the outer cover. There was more in the crankcase but none in the actual oil tank. All that remained of the starter train was the idler gear. This also revealed the neatly implemented gear change crossover shaft, slightly angled back to the rear of the gearbox inner cover. The arrangement included an idler gear on the gear lever shaft to reverse the shift pattern to the ‘standard’ up for up. Thus, the original Commando’s crisp action was sacrificed on the altar of uniformity.
The gearbox had to be fixed in place for the crossover shaft, so the clever chaps at Norton squeezed in a hydraulic chain tensioner. This was a good example of an engineering solution to the challenge of getting more life from those 20 year-old designs. Happily, the triplex chain and sprockets were in good order as was the clutch, other than for having a mixture of bronze and composition plates. The alternator stator looked cooked, but my first real challenge was removing the engine sprocket. This required a puller, heat and numerous blows to the side of the sprocket to free it.
Another difficulty was removing the inner cover, I even checked to see if I had missed a fastener or two. Eventually I applied some rotational force to shear what proved to be ‘Yamabond’ sealant between the chaincase and crankcase.
Following the manual, I removed the front Isolastic mount and proceeded to take out
the crankcase bolts to free the engine for removal. All well and good… but for the bottom bolt that apparently needed to come out through the right frame rail. After a bit of head scratching, I realised that the engine mount pivots on the rear Isolastic so it was a simple matter to lift the crankcase until the bolt head cleared the frame rail.
My plan was to dismantle, inspect and rebuild the bottom end, something I had never done before. The bike only had 15,000 miles on the clock, but even if that were true, it had over 40 years on the calendar and time can do terrible things to a machine. Fortunately, a noted expert in such matters advised asking RC regular Richard Negus if he would take it on. He would, he did. Yes, this was an unbudgeted expense but who better to sort a Commando motor than a man from the original development team? Quite apart from that, regular readers will know very well that the cost of a novice rebuild can be much more.
Delivering the engine bottom end to Richard enabled me to drop off some rusty parts, including the footrest hangers, brake pedal, kickstart and headlamp, for rechroming by Prestige Electroplating. The helpful lady behind the desk remarked that they had some similar parts in before. Yes, she agreed, from a Scottish fellow, possibly named Urquhart…
Richard immediately showed his expertise by removing the timing cover and spotting the lack of a spring and plunger that should stop oil draining into the crankcase. I learned later that some bikes left the factory that way. Other minor issues including a worn timing chain tensioner but the ‘Wolverhampton’ camshaft and its faulty case hardening was a concern. Although it was still serviceable, there were signs of wear and I only wanted to do this job once.
Replacing some parts before their time added to the cost, but I was building this motorcycle to ride, not endlessly faff about with its internals and running gear. As I look back from over 2500 miles of trouble-free riding, I can’t say I have regretted a single penny spent in this way.
There was nothing obviously wrong with the head – with the emphasis on ‘obvious’ but Richard’s sharp eye spotted a cluster of corrosion pits in the barrel – ‘ That will smoke’, and a broken fin (glued back on, but at least it was there). I left him with the bottom end to sort out. Once home, I borrowed a pit gauge and measured the corrosion depth at between 0.1 and 0.4mm so a +40 rebore and oversized pistons were added to my growing list.
Turning to the frame and running gear, I removed the gearbox sprocket after a struggle locking the back wheel without a working brake. The chain and sprockets were badly worn with evidence of the chain rubbing on a lug on the swinging arm and frame rail, so that lot went on the discard pile. The wheels were no trouble to remove, but the front rim and possibly the rear needed replacing. The discs and calipers were in
reasonable condition, so I kept them with the rear master cylinder for refurbishment.
Turning to the switches and electrics, I found the handlebar switch sub-harnesses needed replacing: did I mention the seller describing the electrics as being in good order? Thankfully, the virtually unobtainable switches worked but the main harness multiconnector shells were brittle although the main harness itself could be retained.
The warning light console needed new lamps, decal and attachment bracket. Both the ignition and steering lock keys were missing, as were the front indicators and speedometer inner cable. Checking the clocks with a variable speed drill and tacho cable showed the tachometer was working as was the odometer but there was only a twitch or two from the speedometer needle.
Challenges to come were the swinging arm and rear Isolastic mount, both seized, but the battery carrier, rear mudguard, Girling units, right Z-plate, stand, chainguard and so forth were easily removed. The swinging arm seizure was probably an inevitable consequence of relying on oil soaked fibre pads installed over 40 years previously for lubrication. Happily, the cotter pins came out easily. I then replaced one to lock the spindle and used the other to plug the remaining, bottom hole. This allowed me to fill the central area with Plusgas to soak for a few days. Moving the swinging arm a small amount gradually became easier and I added more Plusgas as it migrated along the spindle. Eventually I could draw the pivot spindle out using the front Isolastic mounting bolt.
Stripping down the gearbox filled the time while the penetrating oil was doing its job. Its internals were in good condition, suggesting this was indeed a low mileage machine. The layshaft wouldn’t budge so I applied a heat gun to the back of the gearbox until it pulled out complete with its bearing. Similarly, a few light taps released the sleeve gear and its bearing.
Apart from the oil tank, sitting on an oily pad of rubber strips bound by duct tape, just the rear Isolastic engine mount with its captive right Z-plate and oil filter remained of the back end. The oil tank was fiddly to remove but just left the stubborn rear Isolastic stud. Heat, an improvised draw tool and violence failed to make any impression so I resorted to thought while carrying on with other, simpler tasks.
This, thought that is, became a feature of this project. Stepping back from a seemingly insurmountable problem before inflicting damage or resorting to an ugly bodge. Focusing on other tasks helped steer my thoughts from what should be to how things were and, importantly, how to solve the problem. Sometimes it would take a few days but, invariably, this would produce the solution and we would move on.
In this case, I reasoned that the stud, passing through the Isolastic mounting was rusted in place. Rust is not an adhesive but
iron oxide has four times the volume of the steel it replaces. When you get that amount of expansion inside a close-fitting steel tube, there is no shifting it. Noting that the stud rotated freely in the frame lugs, all I needed to do was separate its ends from the middle – with a hacksaw.
Carefully sawing inboard of the end washers left the frame lugs safe, with damage limited to the easily replaced thrust washers and adjuster. Once the ends were released, the engine mount and Isolastic core came out easily, still holding the remains of the stud in a death grip.
Thankfully, removing the front forks and yokes, wiring loom and remaining few bits and pieces, including the mysterious ‘blue thing’, was straightforward. Stripped bare, the frame was not a pretty sight, my idea of simply touching up the paint was clearly a non-starter. Not only would it be a right faff, especially cleaning off the petrified duct tape, it would let down the rest of the rebuild. Besides, there wouldn’t be a better opportunity to paint it properly or, in my case, go for the price and convenience of powder coating already planned for the ancillary parts such as engine mounts and stands.
So, mindful of ‘spoiling the ship for a ha’p’orth of tar’, I punched another hole in my notional budget and duly removed the headstock bearings and certification plate…