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…
My Commando was now a collection of parts loosely bound by optimism. The project was at its lowest ebb, a more or less organised collection of crates and boxes of bits. In a state of maximum entropy as Prof Brian Cox might say. It would take energy, enthusiasm and no small amount of cash to assemble those parts into a functioning motorcycle. Perhaps this is the reason some projects fail at this point, where progress, if it is to be made at all, stretches into the distance, uphill.
Resolve and enthusiasm alone were not enough, this required a plan and I had one. Even as I was merrily taking the bike apart, I printed off parts lists and diagrams and highlighted them with red for parts needed and green for those I could reuse. There was an awful lot of red on those sheets as I slotted them into a binder. This had tabbed sections for the main assemblies, diagrams and pages from the workshop manual and, later, my notes, sketches and checklists. Technical data went in the front, headed by my project outline sheets and current task list.
Over-egging it only slightly, I listed the parts needed by group in a spreadsheet. The sorting and filter tools made it easy see what was needed as well as parts already in hand together with pricing and supplier information. So much for organisation, now for the real work.
Ultimately, everything attaches to the frame, so that was my starting point, together with the swinging arm, engine mountings, stands, yokes and sundry brackets. I masked the headstock, yokes, swinging arm and obvious places where powder coat did not belong. What I did not know, but soon
learned, was that there were other less obvious, areas needing to be clear of powder coat.
I came across a series of practical guides to rebuilding a Commando on www.oldbritts. com, including one for masking parts before powder coating. This would have been even more helpful had I found it earlier, but that’s why we have scrapers and Dremel tools.
The guide was very clear about not having powder coating between the crankcase and its mounts. This is because powder coating is thick, soft and creeps from under tight, bolted connections. The loosened bolts then bear the brunt of the engine vibrations rather than transmitting them to the Isolastic mounts resulting in oval bolt holes and, eventually, sheared bolts.
Paint also doesn’t belong where a close fit or earth continuity is required. No doubt opinions vary, as opinions will, but I had no problems with assembly, electrics or loosening bolts after following the recommendations. The guide also points out, unkindly I thought, that blanking off the critical areas is easier and quicker than removing the powder coat afterwards.
Turning to the gearbox, I removed the quadrant, selector cam and neutral switch before beginning the messy job of cleaning the gearbox shell. On the plus side, the gears, selector forks, bearings, bushes and kickstarter were in very good condition. All I needed were new seals and gaskets, but I ordered a new ‘Superblend’ layshaft bearing, sleeve gear bearing and layshaft bush just to be on the safe side.
Given the general state of the electrics, I was pleasantly surprised to find the neutral switch worked. This does no more than light a lamp in the warning light console, so the unwary rider can still engage the starter with the bike in gear. I toyed with the idea of adding it to the starter circuit as an interlock, but not for long. There were enough potential problems in that area without adding more.
A quick risk assessment on the hazards of using the domestic oven for heating the gearbox shell led me to improvise a hot box. Comprising a Roses tin, camping stove, mineral wool insulation and espresso machine drain plate, it easily produced temperatures up to 220°C, as measured by my barbecue meat probe. That was more than enough for me to simply drop the new bearings into place.
Reassembling the gearbox was reasonably straightforward, other than pausing to remove and then refit the layshaft bearing the right way around. The selector forks were a bit of a fiddle, as was adjusting the neutral switch. Backing off the detent plunger helped with rotating the selector cam for this as well as fitting the selector forks and checking gear selection. I was, however, irritated to find that the new seal ‘set’ did not include the ratchet quadrant and kickstart seals.
The manual made no mention of removing the layshaft bush and I couldn’t find anything helpful on the Internet. Heating was no use because the steel shaft has a lower coefficient of expansion than the bush. In the end, I used a mini hacksaw (the type where the blade protrudes from the handle so it can be used in a blind hole) to cut a couple of slots in the bush. This relieved the compression enough to pull the bush out with an improvised draw tool. Leaving its replacement in the freezer for a while allowed it to be drifted in with a few sharp blows.
Remembering to fit the knuckle pin roller first, held with a spot of grease, I fitted a new gasket on the inner gearbox cover with Wellseal on one side and grease on the other to simplify disassembly. Then it was a matter of getting the mainshaft and layshaft lined up with their respective bearings and bush so the inner cover with its kickstart shaft and pawl could be juggled into place. I tightened the mainshaft nut to a nervous 40-50 lb.ft before fitting the clutch lever assembly, taking care to align the lever with the cable entry point marked on the cover.
Assembly of the gear selector mechanism on the outer cover needs patience and precision, especially with the return spring and hairpin pawl spring. The pawl spring is critical for proper gear selection – or any selection at all if it is badly positioned. This is well described in the helpful NOC Service Notes.
The lack of a gear lever to help with positioning the ratchet and checking gear selection made fitting the outer cover difficult. I cut a piece of 0.3” ID steel tube, slotted it at one end and drilled holes for a tommy bar in the other. This allowed it to be secured to the splined quadrant shaft at the back of the inner cover with hose clips. I could then rotate the ratchet quadrant with a tommy bar. Although I couldn’t achieve the happy, symmetrical up and down gear selection described in the Service Notes, I could select all four gears and neutral reasonably easily. Remembering to tighten the detent plunger so it was fully home, I put a large ‘tick’ next to the gearbox rebuild item on my project sheets.
Fitting the new, bonded Isolastic assemblies into their mounts was doubly difficult with frozen fingers and cold elastomer. It took a few whacks with a mallet to start the Isolastic cores in the front and rear mountings respectively. This was followed by careful levering around the rims and additional persuasion for the Isolastics to slide into their respective, well lubricated mounts. From there it was a matter of adding the end caps, thrust washers, abutments and gaiters. The main stand was easy to fit at this point and made for real progress leading directly to installing the engine and gearbox.
I completed the engine bottom end overhaul by bank transfer and collection of the now sparkling engine from Richard Negus. It had not needed too much work but he had replaced the camshaft as we had discussed, big end shells, timing chain, tensioner and a few other bits and pieces including screws and studs. He also supplied a CD with his inspection report and pictures of the work. ‘ Thorough’ doesn’t begin to describe it and I hope or two pictures here will show what I mean.
With nothing on the frame to get in the way, I opted to fit the engine and its mountings as an assembly, starting by attaching the crankcases to the Isolastic mounts with a set of indulgently expensive stainless steel bolts. The front ones were just fine but the rear ones were 1/8” short. This meant the inserts in the nyloc nuts did not engage on the threads and could loosen should there be any vibration (ie. if the bike actually started and ran).
The supplier promised to send replacements once a new batch with the correct thread length was produced. These could be replaced in situ so I carried on and fitted the engine in the frame with the help of a friend with strong arms. We offered up the engine so the rear Isolastic mount aligned with its lugs and allowed me to slide the new mounting stud though to secure it. The front mount was attached in the same fashion with its bolt. That done, I slotted in the gearbox and secured it with its top and bottom mounting bolts, not forgetting the spacer for the top mounting lug.
Oil Tank Troubles
The large patch of epoxy on the bottom of the oil tank was not a good sign, and neither was the untidy brazing around the remains of the original threaded mounting underneath. The only good news was that the tank did not leak, even with the epoxy removed. Nonetheless, the bottom mount needed restoring to the state Norton intended.
I thought about this over the course of fitting the rear mudguard bracket together with the battery tray, rectifier and left panel brackets. Fitting a new steering lock provided one of those ‘ping – soddit’ moments with the roll pin but I managed to find it and get that job done.
You may think that my assembly sequence was a bit random, and you would be right. I have described the rebuild in logical stages, but the same day could see me working on elements such as the wiring, clocks, suspension and possibly a different bike altogether. It was a matter of maintaining momentum as well as keeping the other plates spinning. Except where the assembly sequence was important, if I was held up by one task or just needed to think, I switched to another. My spreadsheet, notes and task lists were very helpful, if not vital, for keeping track under these circumstances.
My oil tank repair involved cutting a steel patch plate to fit over the damaged area to avoid disturbing the brazing that at least kept the oil in. A friend let me use his lathe to make a threaded boss to replace the original and Flavell’s of Thornaby did a fine job of welding the plate and new bottom mount in place. All that remained was for me to add a couple of coats of paint.
Metalastic mounts are not confined to the engine. Two bobbin type mounts, attached fore and aft at the top, secure the oil tank. The bottom is fixed to the battery tray by a ¼” UNF hex screw. This is difficult to fit and can cause cracking around the bottom mount if one or both top mounts break, and break they do. The result is the sort of compound bodge of brazing, epoxy and duct tape encountered with this one.
Given that it is secured by its top mounts, the job of the screw is to locate the tank bottom on a grommet in the battery tray to stop the tank flapping about. A simple peg could do that, so I threaded a piece of ¼” rod and screwed it into the new bottom mount before fitting the tank. The peg made this a little more difficult, but it located in the grommet as intended, preventing lateral movement while allowing some vertical flexing of the top mounts.
Fitting the oil filter, new oil lines and their newly painted flexible steel sheaths was simplified by the absence of rear mudguard, swinging arm and main stand. Another task complete and checked off in the project file.
A Two Carb Problem
Twin carburettors seem an unnecessary complication, at least in the context of classic motorcycling. The extra top end performance hardly seems worth having a poorer response at low rpm and the pain of getting the carbs tuned and synchronised. My Tiger 650 works very well with its single carburettor so why not the Norton?
To say I agonised over this would be to overstate it, but I had a lot of trouble making up my mind. Going to a single carb would cost more, mainly because of the need for a two-into-one manifold, but not enough to be a deciding factor. Also, I had planned to use the original airbox as it carried the top attachment bracket for the left panel. The airbox could be modified for a single carb though and I went as far as to start making an adaptor plate for this.
Seeking advice from a higher plane, I asked Richard Negus for his thoughts. His reply, typically to the point: was that the airbox was too restrictive and only there because of tighter US noise regulations. He recommended a K&N filter specifically intended for the Commando twin carb setup. Decision made: I would persevere with the original twin carburettors but ditch the airbox. I am still not sure this was the best decision, but I subsequently learned a great deal about setting up a pair of Amal Concentrics.
There was no going back. The airbox could not be fitted once the barrel, oil tank and battery were in place. Fortunately, RGM were happy for me to return the new filter and other parts I had bought to replace those missing from the airbox. That done, I set the carbs aside for another day, a much later day as it turned out.
Fun With Forks
Now for the famous, if by 1975, dated, Roadholder forks. More new territory for me but, with guidance from the workshop manual and on-line material, the job of stripping and cleaning them was no trouble. They were in very good condition and only needed new seals and gaiters, although I replaced the rusted top nuts as well.
Even fitting the yokes was a snap thanks to the easy to fit, original sealed steering head bearings. Filling with fresh fork oil was tricky because the damper rods and instrument pods take up most of the space at the top of the stanchions. I used the recommended SAE-20 oil but have seen ATF recommended for an easier fork action. All that remained for now was the fiddly task of tightening the new top stanchion nuts to the specified 30 lb.ft while keeping the instrument pods in their correct positions.
I left the new swinging arm bushes soaking in oil for several days before pressing them into place with the new seals using a vice with soft jaws. With its new spindle and bushes, the swinging arm was a tight fit. Not a bad thing, but it made lining up the cotter pins difficult. All being well, it should bed in once we reached that still far away time of racking up some road miles.
Those of you unfamiliar with the Commando may be surprised, as I was, by just how much load the rear engine mount carries. It doesn’t just hold the engine, primary chaincase, gearbox, oil filter and centre stand, it also carries the swinging arm and, effectively, the rear wheel. This is good practise because it puts the swinging arm pivot in close to the gearbox sprocket to minimise changes in the chain tension with
suspension movement. It also ensures the sprocket alignment isn’t disturbed by flexing of the Isolastic mounts.
On the down side, the engine mountcum-subframe adds considerably to the otherwise light 24lb frame, putting it nearer to the Featherbed’s 34lb. More seriously, any slop in the Isolastic mountings will cause some interesting handling as the swinging arm explores the resulting lateral freedom. Correct adjustment of the Isolastic mounts to minimise lateral movement and regular checks on the many and various nuts and bolts is essential.
Lubrication for the swinging arm bushes relies on oil-soaked wicks at the ends of the spindle. That’s it! Sealed for life as they say. But how long is that? Copying the well-tried arrangement for AMC heavyweights and earlier Commandos, I drilled and tapped a hole in the right-hand Welch plug and sealed it with an old fork leg drain screw. This would allow the addition of oil from time to time. A corresponding hole through the right spindle wick allows oil through to the left side. I sealed the Welch plug itself in place with silicone rubber rather than the intended thump with a drift. Only time will tell if this proves effective.
Bolting on new NJB rear suspension units finished the job, although I later found they were a little longer than specified and, if anything, I needed shorter ones. No problem, an understanding Norman Blakemore was happy to make up a shorter pair, as a straight swap for the standard ones.
Left: The Commando project folder, my security blanket!Below: The Commando frame is well designed and light, probably half the weight of an AMC heavyweight frame and 10lb less than a Featherbed. The problem is that just about everything attached to it is heavy. Leaving the swinging arm bushes in place to mask the bush mounting holes was a mistake. The powder coaters had a big problem with oil sweating out of the bronze bushes when hot. Fortunately they manged to overcome it
Left: Rear engine mount: removing powder coat from critical areas. The final step was to apply a thin coat of paint to protect the bare metal. This is a vital component carrying as it does the gearbox, crankcase, rear suspension, centrestand and, effectively, the rear wheel
Right: Masking washers for the Isolastic are still in place. The final step was to apply a thin coat of paint to protect the bare metal
Right: The essence of a Commando, ingenious and reasonably effective solution to taming the vibrations of a supersized late 40s engine. Even so, it could only buy some time to design and build a modern motorcycle. Not enough time as it turned out
Left: Just keep adding bits until all the crates are empty…
Note the narrow ligament between the bearings, this can crack with hard use or ham handed bearing fitting. The inner race of the smaller, layshaft bearing is flanged and should pull out to be fitted on the end of the layshaft. In this case, the inner race flange is at the back of the bearing and requires a second visit to my hotbox
Camplate and quadrant fitted. Looking good, no wear evident
New big end shells fitted and the crankshaft halves bolted together
A ‘Wolverhampton’ cam starting to wear. Serviceable but probably not for long
Crankshaft halves in excellent condition
Just clean them up and put them back
Engine and gearbox installed. You can see the potential already
If the kickstart starts rotating on its own with the engine running, this bush (and possibly more parts) need replacing
Outer cover with temp gear lever fitted. Note the neutral switch below the improvised gear shift
Rebuilt engine bottom end. Richard Negus works fast; I was still taking the bike apart at this point
Oil pump and new timing chain and tensioner
Reassembling the crankcases and crankshaft
Cogs back in the box. Getting the hang of this gearbox assembly stuff…
The forked clutch arm must align with the clutch cable entry point
Main stand fitted. The design allows the spring to be fitted first so you can use the stand legs as levers to line up the mounting holes and fit the bolts
Fitting the steering head bearings. The red plate is the replacement certification plate carrying the machine (engine) number and date, carefully stamped by me. It is not much more than decoration as the DVLA go by the frame number. This wouldn’t matter if HM Customs hadn’t logged the machine number on their NOVA import certificate rather than the frame number
Forks stripped. Just need a good clean and reassembly with new seals, gaskets and so forth
Forks refurbished. Oh those gaiters again … but another task completed
Sensible, sealed ball bearings mean no faffing about with individual balls spilling out of their tracks as you try to fit the yokes. Nothing to adjust either
Above: Original airbox with part-finished adapter plate for single carburettor use. This was abandoned in favour of retaining twin carbs with a free flowing K&N air filter
Left: Note the mounting lug for the brake calliper on the left fork slider. This change, from behind the right fork leg, was to cure the problem of the earlier 850’s pulling to the right even when the brake wasn’t being usedBelow: Swinging arm and new parts. Another weighty object … but it probably needs to be!
The modified Welch plug. Very difficult to access once the Z plate and rear brake master cylinder are fitted. This may be why Norton opted for the oil soaked felt to keep the swinging arm lubricated. Note the oil filter tucked in under the swinging arm mount
Left: Swinging arm fitted. Note the rubber plugs to keep the weather out of the cotter pin tunnels. They worked, too
The story so far. Oil tank and shocks fitted, along with the instrument pods. Note the rear frame loop and the complete lack of support or bracing. This needs to be borne in mind before fitting a rack or panniers
Oil tank repair plate and boss. A fine piece of metal bashing and turning, even if I do say so myself
One oil tank bodge. Could have been worse, he might have used chewing gum…
Oil tank patch welded in place. Much less than a new tank