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 5: Primary Drive, Pistons and Paint
All in all, it was a proper pickle. Tightening the clutch hub nut had overwhelmed the retaining circlip at the back of the hub and somehow locked the gearbox. It looked as though the mainshaft had been pulled out, but that was not possible. Had I not tightened the nut securing the other end and taken its picture? No, the gearbox sprocket and sleeve gear must have been pushed back into the gearbox and that would have the same effect. In any event, there was nothing else for it but to dismantle the gearbox and primary drive, and start again.
That was easier said than done. Getting the inner chaincase over the jammed spacer meant destroying the mainshaft seal but gave me access to the circlip so I could remove it and go on to dismantle the gearbox. If nothing else, this showed the benefit of using jointing compound on one side of the gaskets with grease on the other. Not only did the covers come off easily, I could leave the gaskets in place for reassembly.
With the cogs out of the box it was clear that the sleeve gear had moved, so I drifted it back out to seat against the bearing. It was then a matter of retracing some old ground as I refitted the mainshaft and gearbox internals, taking the opportunity to put a thick washer under the selector detent nut to make gear selection easier.
The new circlip finally arrived with other parts I had ordered and reminded me that few suppliers match RGM’s typical next day service. Mindful of Einstein’s definition of a fool: one who repeats the same process and expects a different result, I looked closely at the circlip and clutch hub spacer. The spacer has a recess on one side that should fit over the circlip to prevent it spreading under load. Clearly, I hadn’t seated its predecessor properly before tightening the hub nut.
Understanding the original failure gave me confidence to try again, beginning with a dummy run before installing the inner chaincase and primary drive. I torqued the nut up to 50lb.ft with just the clutch centre,
circlip, spacer and shims in place. Nothing moved so I removed the hub and finished reassembling the gearbox.
I was relieved to find there were still four gears and at least one neutral, but irritated by difficulties with stopping a small leak from the back of the rear master cylinder. This had to be removed to access the gearbox cover and proved a chore to refit.
With that job done, I refitted the inner chaincase, engine sprocket, primary chain and clutch, carefully checking the circlip and spacer. The torque reading climbed steadily as I nervously tightened the clutch nut, finally reaching 70lb.ft and leaving me with the simple task of bending the tab washer over.
I later read that the specified mainshaft torque is too high, with a recommendation to use a lower value of 40lb.ft. This was on the NOC site, but it gave no basis for the lower figure so I stayed with the factory setting.
Breathing a sigh of relief, I fitted the clutch plates, pushrod and diaphragm spring with its retaining large diameter, double ring circlip. On went my new clutch cable followed by adjustment to the pushrod clearance to produce a working clutch.
My mood lifted as I reassembled the primary drive, including the alternator and chain tensioner. I checked the rotor clearance with an 8-thou feeler gauge and found it was an easy fit all round. That left the chaincase steady nut to tighten and the gearchange crossover shaft to slide across to its splined sleeve connector on the gearbox selector quadrant.
Panels and Paintwork
There were two problems with my new, fibreglass left panel. One was the loss of its upper mounting bracket in the absence of the airbox. The second was that its bottom locating tab did not fit behind the Z plate as it should. The tab has a thick grommet fitted to make it a snug fit between the Z plate and battery tray after locating the rear of the panel on a peg attached to the rectifier mounting plate below the solenoid.
A patient Les Emery explained that the Dzus fastener mounting on the lower edge of the battery tray should not be there. Cutting off the offending bracket (that Dremel tool again) solved the problem. That left me to make a bracket for the upper panel mount and to find a suitable Dzus fastener. I attached the bracket to the frame with an extra grabrail clip and adjusted it so the panel was held in the correct position. Now I could prepare for painting.
My experience and that of others suggested that lining the petrol tank would be more trouble than it was worth. The tank’s inside surface looked sound but needed a good clean, beginning with a thorough flush with degreaser. I then amused myself by shaking a double handful of discarded Norton nuts, bolts, screws and washers around inside the tank to shift what I could of loose paint and scale. The final step was to treat it with a passivator to give the surface some protection.
My choice of colour was in no doubt, Candy Apple Red, by far the best colour for a Commando. Apparently, the factory thought the same because I found the left panel was originally red and, later, the factory record confirmed that it had been dispatched to Canada as a red bike.
My initial search for a good, local spray painter fell flat but I was pleasantly surprised when my daughter handed me a
business card for Sarah of Saragon Custom Paint in Darlington. A young, possibly hopeful, lad had chatted to her about his bikes while she was working her shift at our local Sainsbury’s pharmacy. I don’t know how it came up, but he recommended Saragon and gave her the dog-eared card. Soon after, I talked to a rider on a VMCC run whose bike had a very good paint job. He also recommended Saragon which was good enough for me. Sarah worked out of a small lockup unit with just about enough room for her stock in trade of custom painting bike helmets, tanks and panels. She obviously worked to a high standard, but it was her enthusiasm that I really liked.
She knew exactly how Commando tank and side panels should be painted, including the lettering and pinstriping, and no, she did not want the decals. Taking a deep breath, Sarah explained, carefully, having dipped fingers in cans of Candy Red and Silver Flake to make the point, that she would firstly spray with Silver Flake, then mask the tank and panels with diecut logos and lettering. She would then spray the Candy Red on top so that the Silver Flake base gave it that special lustre. The final stage was to remove the masking, apply several coats of ethanol-proof lacquer and finish it off with high-quality wax polish.
So, leaving my tank and panels in Sarah’s capable hands, I continued with the mechanical work and fitted the now gleaming outer chaincase, gear pedal and left footrest. When I returned some weeks later I could hardly believe the transformation from pitted and dented dreary black to smooth, shining Candy Apple Red. This was really good work and at a reasonable price
considering the time and effort involved.
Once safely home, I rinsed out the tank and fitted the original filler cap with its new seal. New rear rubber mounts, a replacement rear mounting strap and cleaning the paint from the fuel tap sealing surfaces finished my preparation for fitting the tank.
Top end troubles
The news from Morpeth was mixed. My barrel was done, with each bore sized to suit its respective piston. This was a matter of tens of thousandths of an inch and I like that level of detail. The head, on the other hand, had a big chunk of alloy broken off behind the left exhaust seat. A picture of it showed the classic cleavage surface of a brittle fracture, possibly from someone attempting to fit a new seat with an excess of force and inadequate heat. This would tie in with the obvious work done to smooth the ports, but didn’t fit with an engine that had done so few miles.
Whatever the case, it was a serious problem. Richard Negus said he would try to get the damaged seat area built up with weld. He could then machine it back to its original shape to accept a new seat. Short of buying a new head, this was the best plan. I collected the pistons and barrel anyway so I could continue with that part of the rebuild.
As was the case with the frame, the barrel finish looked reasonable at first sight, but it didn’t stand closer examination. I had heard of stove enamelling as a suitable finish for barrels, but wondered how different this was in practice from powder coating. The powder coater I had used for years hadn’t had any problems with motorcycle barrels, although iron heads get too hot around the exhaust port. I cleaned the area around the broken fin where it was joined to the to the barrel and reinforced the joint with thin aluminium plates bonded with JB Weld before taking it to the powder coater.
The beautiful, shiny black barrel was back within a week. I rinsed and cleaned out the bores, oilways and pushrod tunnels and then lightly oiled the surfaces. This process revealed a small slug of silicone rubber in one of the oilways that had resisted all the cleaning and flushing. I hooked it out with a mini pick and breathed a sigh of profound relief that I had found it at this stage of the rebuild.
Work on the cylinder head was still progressing. I was happy to hear that the weld repair was successful and Richard would shortly get down to the machining work. Meanwhile, I fitted new coils to the replacement coil bracket. This required making up some spacers so the coils sat just clear of the bracket sides. The bracket had room for the Pazon ignition module to sit between the coils, where the ballast resistor would have been, so I made a top hat section bracket to hold it there.
Having enjoyed another day out in Northumberland to collect the head and tappets, I began work by cleaning out the inlet and exhaust ports before fitting the rockers and valves. Richard had advised against use of the deceptively named vapour blasting because it is a water-borne abrasive and there is a risk of abrasive slurry remaining inside the head. This was all very well, but my attempts to clean it with solvents and wire brushing hadn’t been effective. Besides, with the valves installed, I could easily seal the head with the rocker covers and blanking plates over the inlet and exhaust ports. Screwing in
a couple of old spark plugs and fitting caps over the oil inlets completed the job, so I could drop the head and carburettors off for ultrasonic cleaning and aqua blasting.
That left me to fit the refinished tappets and fit the barrel. This was not the easiest of tasks single-handed, but I managed it with the help of a couple of modified automotive ring compressors. There is no cylinder base gasket and the manual recommends the use of Loctite Plastic Gasket. This is because the barrel cannot be torqued down after some initial running unless the head is removed. Itself no easy task. Other brands are available and I used one of them but, as I had already seen, application of any liquid sealant needs to be done with care to avoid plugged oilways.
Norton thoughtfully fitted a timing scale inside a port on the front of the primary chaincase so you can check the ignition timing. I used a dial gauge to measure the piston depth corresponding to 32o before top dead centre. I marked this on the rotor with a punch mark and a blob of red paint for future reference. This set-up also allowed me to fit the Pazon trigger module in the points housing and set it to a slightly retarded 31o fully advanced, compared to the Pazon-recommended 32o BTDC and 28o for the original points and mechanical auto advance. This increased advance setting is possible because the electronic ignition has a more accurate, broader advance curve and the full retard setting is unaffected.
The cylinder head positively gleamed as I removed the blanking hardware but to underline Richard’s point, there was abrasive that needed cleaning out from the headsteady screw holes. So much for the ‘double washing’ after blasting! Just to make sure, I checked the narrow rocker oilways and they were clear. The head jointing face was a bit careworn, so I rubbed it down on some 400grit wet and dry paperr backed by a flat glass plate before fitting new stainless steel locking caps and screws to secure the rockers. The head was ready to fit but, firstly, it was time for a fortifying cup of tea and large piece of cake.
Fitting the head was every bit as difficult as I expected, but after removing and refitting it twice I was getting the hang of it and the
third attempt worked, almost. I was able to torque down the head bolts and nuts, but could not set the right exhaust rocker clearance because its pushrod had jumped out of its cup and jammed. Luckily, I could reseat it without disturbing the others, and so fitted the rocker covers and moved on to the exhausts.
Exhausting Times
The silencers were peashooter types rather than the bean cans fitted as standard – Commando owners certainly like their legumes! There was some damage to the right-hand silencer, including some minor dings and a rusty patch possibly resulting from battery acid leakage. Unlike the exhaust pipes, they were useable but the mounting brackets did not match and were probably the originals made for the bean cans.
With new front pipes and the correct silencer mounts on order I cleaned up the rusty patch on the right silencer and painted over it with silver Hammerite. My plan was to fit it on the left side so the damage did not show to anyone who was not lying beside the bike and looking up.
It was just as well that I was fond of Meccano as a kid. The need for frame isolation meant that the kit of plates, spacers mounting rubbers, nuts, bolts and washers went far and beyond your typical silencer bracket. The assembly included the pillion footrests, so that was some more parts out of my rapidly emptying boxes of bits.
A trial fit of the new exhaust pipes showed that they didn’t… fit, that was. It also revealed that, not for the first time, brake fluid was weeping around the rear master cylinder pipe joint. I tightened the offending joint and swore at it. This, surprisingly, worked and I have had no trouble since.
Admittedly I had bought Mk2A 850 pipes, but I could not think of a difference between the two 850 frames and engines that would cause the right pipe to rub up against the frame rail, and the left one to have minimal clearance from the primary chaincase and sidestand. There was nothing to gain from complaining so I made some spacers to push the silencers and pipes clear of the frame. Gritting my teeth, I put a small dent in the left pipe to clear the low point of the primary chaincase.
This tricky bit of fettling produced enough clearance for me to fit the collets and seating rings in the exhaust ports and tighten the exhaust lock rings. The fit remained acceptable after tightening the new, stainless exhaust clips and silencer mountings. It all
looked good too, especially with the tank and seat dropped into place.
At this point I had also fitted a few other parts, including the tachometer cable, a rather ugly but loud stainless steel marine horn and new rocker feed lines with stainless steel banjos.
Steady on there
A Mk3 Commando head-steady has thirtyfive parts including the fasteners. There is the head-steady itself, Metalastic mountings, plates, trunnion, spring, brackets and various fasteners. Had I known just this much about this model, the outcome of that pre-bid viewing might have been quite different.
It was only after a fruitless search through the parts box that I realised I had sold the spacers with the earlier type head-steady fitted to the bike when I bought it. These were simple to make from some ½” heavy wall stainless tube I had to hand. Less simple was the task of fitting the many and various other parts and getting them to line up, but I got there in the end.
The head-steady tension spring required adjustment but, presumably because of a difference in the pattern part spring rate, I couldn’t match the factory setting. The spring is there to help support the engine and provide a pre-set bias to the head-steady mounts. This improves isolation at low rpm. I set the adjuster to an intermediate position as a basis for tweaking the spring tension after some test runs.
Fitting the head-steady spring retainer included the coil bracket assembly. This attaches underneath and holds the retainer in place on the mounting plate behind the headstock. With that done, I connected the Pazon ignition module, the coils and trigger module. Making up a couple of short HT leads with suppressor caps finished the job as far as the ignition system was concerned.
All I needed now was fuel and carburation to set me on the home straight…