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 6: Fuelling Follies and the Joys of Riding
Moving south to the flatlands of Lincolnshire disrupted work on the Norton and a great many other things besides. My new shed was just as cramped and draughty as the old one but lacked the former’s ready access to the open roads and sweeping vistas of the northeast. On the plus side, there was room for a proper shed and opportunity to explore new horizons, but I digress.
With the bikes safely installed and all the shed paraphernalia sorted out, I tackled the carburettor rebuilds and wondered how I would fare setting up a pair of them. The bodies were back from having the ultrasonic
cleaning redone after I found deposits remaining in the pilot jet air passages. I don’t know why I did not check that they were fully cleared out this time … but I didn’t. That simple step would have saved me much trouble and pain later. So would buying a new pair of carbs, come to that, and for not that much more money. No, that would have been too easy as well as going against the grain of keeping as many of the serviceable parts as I could.
Assembling Amal’s MK1 concentric carburettor was familiar territory. Too familiar perhaps and leading to a what I can only think was a lack of focus. Complacency if you will. I fitted new parts throughout including slides, springs, needles, ticklers, stay-up floats, and larger main jets as recommended for the free-breathing K&N filter. I went so far as to check the fuel levels with the new floats and adjust them so they were the same for each carb. I am still not sure this was necessary and it was a fiddly job to say the least.
One aspect of this and other work on my old bikes that I really do enjoy is making some of the smaller, simpler bits and pieces. It can save time too, reaching for a modest stock of parts and a few hand tools rather than placing yet another order and waiting for the postman. Starting with the easy job, I made up the fuel lines with crimped end fittings and a hose to run from the oil tank
breather to the back of the air filter.
Making up control cables takes more than a Stanley knife and crimper but is largely a matter or care and patience. There are plenty of ‘how to’ guides available including features from the short trousered days of RealClassic (28 and 29). Certainly, making up throttle and choke cables for a Commando gives plenty of scope for practise: four cables from the carburettor slides to the splitters and one each from the splitters to the twistgrip and choke lever. The choke cable has an in-line adjuster so that’s six inner cables and seven outers to measure very carefully and cut, twelve nipples to solder and fourteen ferrules to crimp. This was thoroughly absorbing work, almost therapeutic once I had my production line going, and it really improved my soldering technique.
Fitting the carbs is not easy on a Norton twin because they butt up against each other. In fact, the radiused inboard flange edges must be machined flat for them to fit at all. Then they must be bolted to their manifold stubs before attaching them to the head. This gives good access to the manifold stub outer screws but requires the use of a grounddown Allen key for tightening the inner ones a fraction of a turn at a time. Triumph rockers and pushrod tunnels have their problems, but the splayed head design is far more mechanic friendly. Even so, the Norton’s carbs just needed some dexterity, patience and a little grumbling. Once they were in place, I fitted the fuel lines, air cleaner and carb slides with their new cables.
The tricky thing with twin carburettors is that they must be matched and synchronised so each cylinder is fed the same amount of the same fuel mixture at any given throttle opening. There are well-tried ways to tune Amal and other carburettors dynamically, such as with vacuum gauges, plug chopping and testing the throttle response at different openings. None of this is remotely useful until you have the engine running, and that means getting the initial settings right. This is described in the various guides to be found online including ‘Bushman’s Carb Tuning Secrets’ specifically for the Amal Concentric.
The correct pilot mixture is vital for starting, so I set the adjusters to their recommended 1½ turns out. I then checked
that both throttle slides moved up the maximum amount and adjusted the cables so the backs of the slides were just proud of the carburettor bores. The next step was to trap two equal diameter drills (about ¼”) under the slides, then screw in the throttle stops so each drill just started to dip as the pressure of the slide was relieved. After some back and forth to find the spots where the screws just touched the slides, I marked the throttle stop positions for reference. This synchronised the throttles and was only slightly improved by using vacuum gauges later, after over 1000 miles of riding.
All that remained was to adjust the choke slides and fit the air cleaner. The next tuning step was to start the engine, but I was some way away from that, in fact much further than I expected. Carrying on with the preparation, I primed the rocker boxes with oil, fitted the fuel tank and connected the fuel lines. This also seemed a good time to put oil into the primary chaincase, gearbox and oil tank, not forgetting to slosh some petrol into the tank.
Slackening off the oil line junction block at the back of the timing chest until oil started to run out before retightening it primed the oil feed line. I then turned on the ignition, checked for sparks and was surprised to find there were none from the right plug. Accurate wiring diagram or not, I had connected the link wire between the coils wrongly. I had also made it too short to connect to the correct terminal, but quickly made up another and soon had both plugs firing.
There are several recommendations for preparing a rebuilt engine for starting. I followed the ‘kick it over for five minutes’ routine. Even with the plugs out it wasn’t that easy, but after a few extra kicks for luck I fitted the plugs and turned on the fuel. Now then, tickle both carbs but do not flood, choke closed and a couple of priming kicks (by golly that’s hard). Finally, I could no longer put off the moment of truth and turned on the ignition before launching into a mighty kick. Then another, and another, and a few more.
I am not sure what I expected but it was certainly more than the occasional cough with at least an attempt at running. Part of the problem, I thought, was that I found it very hard to build enough momentum to get over the compression stroke and give it the chance to fire. I even tried one pot at a time but although both cylinders would fire occasionally, the engine would not catch and run.
Now you would think that, by this time, I had really settled into the habit of thinking things through before going any further. But no, the madness was upon me: it would go on the next kick, surely. My right leg was tired so I tried with my unpractised left. A few kicks later had me laid out on the floor nursing a sprained ankle. No, it hadn’t kicked back, but it came up solid on compression and my own inertia did the rest. That at least gave me plenty of time to think as I hobbled around for the next few weeks waiting for the swelling to subside.
Starter rollers, that was the answer, perhaps? I would have tried that had I been able to lay my hands on such a thing, but I knew that I really needed to find and fix the underlying problem. This whole ugly business of kicking the engine over made the electric start even more appealing, so I ordered the parts to go with the uprated, 1.4hp starter motor I already had. Fitting the starter was a longer-term prospect but my right
leg really needed the help.
There was nothing else for it but to go through everything again. One plug had a suspiciously high resistance reading for the centre electrode so I replaced it. My fuel level measurement rig had created a higher head pressure than from the tank. This led to low fuel levels with the carbs fed from the tank, so I readjusted them using a more realistic reservoir height.
My first oil leak appeared but was easily fixed with a screwdriver applied to the finger-tight oil tank drain plug before getting back to the starting ritual. This time I found the left cylinder would fire consistently but not n the right. The right plug was bone dry, obviously o getting no fuel, and it did not take t long from there to find that the pilot jet airway a was blocked.
My, how it was blocked, too. The only way to t completely clear the airway and the pilot jet itself it was to drill out the blanking plug on the opposite o side of the air screw – as suggested by b Bushman. This gave direct access to both sides s of the tiny (0.016”) jet so it could be cleared c with a fine jet cleaning wire. I then tapped t the hole 2BA and plugged it with a cutoff o pilot jet screw. Not taking any chances, I cleaned c out the left carb pilot jet and its airway too t by flushing with carburettor cleaner.
After all that, what choice did the motor have h but to start? Second or third kick as I remember, r and it ran well too. There was a good g oil return, the engine was remarkably quiet, q especially to the ears of a Triumph rider, and a the sound from the exhausts was glorious. I used a Colortune plug to refine the pilot jet and a throttle stop settings while taking care to
keep the slides synchronised. The result: first kick starting and reliable idling, now that was what was more like it.
I checked the head bolts, although only the top four pulled down a little further. There was nothing for it now but to ride it out into the sunshine for a brief tour around the estate. Gear selection could, should have been better, but they were all there and the brakes worked.
There was a small leak from the right fork drain screw that I sealed with silicone rubber. I checked the timing with a strobe and set it to 26-27o at 3000rpm and then booked an MoT test. Not that there wasn’t more to do. The frame number was hidden, so I carefully exposed it with the Dremel and flapper wheel and then covered it with clear lacquer. Some clod had drilled the threaded holes out of the mirror stem mounts, so I repaired them with thread inserts and fitted the mirrors.
Now I was ready for the MoT, and so was the bike after topping up the oil and front brake fluid. It is less than a mile to the garage so there wasn’t much time to get acquainted and to get used to the right-foot brake. The engine pulled well and the brakes were good, very good in fact compared to my drumbraked bikes. It was a big lump though and it felt top heavy so, being short of leg and light of weight, I was a little nervous of wheeling it around and stopping at junctions.
I pulled up next to an immaculate red E-Type at the garage and had a brief chat with the owner as our respective machines gleamed in the sunshine. Half an hour later I had my MoT ticket and a more relaxed ride home. All I had to do now was get the bike registered.
The job’s not finished until the paperwork is done
The DVLA application for registration of a used motor vehicle ( V55/5) wasn’t difficult to fill out, especially with the helpful notes that came with the Norton Owner’s Club dating letter. I also had a copy of the original factory record, the MoT ticket and the all-important ‘NOVA’ import certificate. What could possibly go wrong?
I’ll give them their due, the rejection letter from the DVLA came back in short order. Their reason was far from clear though: ‘Following a check on the date of the NOVA letter, it is necessary for you to contact HMRC before we can process your application’. Several phone calls later, I confirmed that the problem was that HMRC referenced the machine certification plate ( VIN) but the DVLA would only accept the frame number. That the factory record showed both numbers belonged to the same machine cut no ice whatsoever.
Another call, this one to the HMRC Personal Transport Unit in Belfast, was more successful. A lovely, patient lady listened to my tale of woe arising from the machine number mismatch. ‘I can change that’, she said. ‘Just tell me what the reference number should be.’ No forms, supporting documents, pictures or fees. Just a clatter of keys and it was done. I spluttered my profound thanks, wished her a good day and went back to my DVLA paperwork.
Shakedown runs
My logical self said this was effectively a new bike, one put together with great care and precision, carburettors notwithstanding. On the other hand, nagging self-doubt and old bike experience insisted that it would fall apart at the first opportunity, where there was no phone signal. I mean, look at the pig’s ear you made of those carburettors!
So, a series of runs close to home seemed in order. The first, some 15 miles, went splendidly although the gearchange was still poor and the gear lever rubber disappeared into the Lincolnshire countryside. So far so good, but this was mid-September and my plan was to get at least 500 miles on the clock for the first ‘free’ service.
Another day, another, longer run after topping up the oil and adjusting the clutch. This was a faster round trip of 70 miles to RAF Waddington for a cup of tea by one of the Vulcan bombers that bombed Port Stanley airfield in 1982. The Norton cruised comfortably up and down the A15 at 5065mph on the 1/3 throttle recommended by the rider’s manual. The gearchange was much better too, but I noticed oil was dribbling down the back of the oil tank before running along the swinging arm and lubricating the brake disk. At least there was no danger of it locking up now.
That one took some time to solve, and I am still not sure exactly what was happening. The leakage stopped at some point after fitting a new filler cap and washer, tightening and refitting the oil lines and avoiding having the oil anywhere near the maximum level. A related problem was the tendency for oil to run down the breather pipe, into the air cleaner and down over the back of the engine. This was solved by fangling a catch pot along the lines of the original but long gone oil separator. Hardly any oil collects with this arrangement because it eliminates the negative manifold pressure that was drawing oil down the breather.
I kept checking fasteners, especially the engine mounting bolts, as the miles accumulated. Indicator stalks loosened as did the mirror stems and rear light bracket. The gearbox level plug and tail lamp fairing screw went AWoL but these and a few other loose bits were quickly sorted with spanners, a couple of replacement screws and Loctite. I also experimented with the head steady retaining spring adjustment and found a setting that minimised low speed vibration at least as far as the rider was concerned.
Most of all, I was increasingly enjoying the rides, and was getting used to being perched on the bike rather than being at one with it. Though still not completely confident on it, I found the Commando’s performance, ride and handling impressive even with limited throttle openings. It steers well and is very stable on the often poorly surfaced bends characteristic of so many roads these days. Add to that the 850’s impressive torque and you have a machine that is a joy to ride on fast A-roads. The acceleration is remarkable, not so much scalded cat as raging bull. The fuel consumption is good too, usually over 60mpg. Something important for a bike with a measly 2.4g (11-litre) petrol tank and perhaps a result of the bigger, 21t, gearbox sprocket and restricted throttle openings.
Before I knew it, mid-October arrived with over 500 miles ridden around rural
Lincolnshire and Rutland. Kicking it over on cool mornings was increasingly difficult but I had no trouble starting a warm engine. A success, what else could I call it? More to do, of course, but I had a reliable, leak-free engine and a bike that really worked. I had what amounted to a new Commando for much less than the cost of a professional restoration, had thoroughly enjoyed the project and had learned a great deal. A bargain, then.
Looking at the bike and its gleaming paintwork as it cooled in the evening sunshine I thought of where this started. Flawed design or not, they really got the looks right and I now understand why Commando owners love their bikes. Now it was time to update my records, clean the bike and plan for its extensive ‘first’ service and fitting of the electric start in time for next year’s rides. Furthest run: meeting up with Frank W in Shropshire – a long way from Lincolnshire