NORTON MODEL 7
Many classic motorcycles are sold after being in storage for moore than a wee while, and are in need of ‘recommissioning’. Stuart Urquhart explores exactly what that might mean, as he makes the acquaintance of Norton’s first post-war twin
Many classic motorcycles are sold after being in storage for more than a wee while, and are in need of ‘recommissioning’. Stuart Urquhart explores exactly what that might mean, as he makes the acquaintance of Norton’s first post-war twin
As WW2 drew to a close, the UK’s motorcycle industry underwent massive efforts toto move production back to civilian supply. However the sudden withdrawal of military contracts hit the industry very hard, as did global rationing of raw materials. As a result, the UK’s factories couldn’t cope with a growing post-war demand for new models. To meet the shortfall in the UK’s showrooms, many dealers simply bought up ex-WD machines and painted them black.
However, it wasn’t long before the major manufacturers, including Norton, converted their pre-war models into post-war models by adding telescopic forks and chrome plated petrol tanks. Initially Norton continued to produce their popular pre-war 16H sidevalve model with girder forks, and only their ohv Model 18 and ES2 singles were updated with telescopic forks. Meanwhile, the launch of the Triumph Speed Twin in 1937 inspired other UK manufacturers to develop their own vertical twins in order to remain competitive. Many had been working on prototype twins before the war, but to Norton management this must have seemed an alien concept – especially as their competition singles had netted the Brummie manufacturer no fewer than 22 Senior TT victories. Consequently it was 1949 before Norton, rather begrudgingly, launched their first 500cc vertical twin at the Earl’s Court Show. Labelled the Model 7, the new motorcycle was largely based on their pre-war ES2 single, but fitted with Bert Hopwood’s newly-developed ohv twin engine. Advertised in Norton’s model line-up as the Dominator, it was a twin that would enjoy successful production, relatively unchanged, right up until the launch of Norton’s sensational Commando almost a quarter century later.
With much of its originality still intact, RC member Iain’s 1950 Model 7 has the aura of an unrestored machine. The bike was formerly sold by County Motors of Kirkcaldy and had remained in Fife until Iain bought it in the 1990s. He subsequently restored the machine in his living room, until work intervened and Iain moved lock, stock and barrel to Angus. Not long after, the Model 7 was featured in the 1997 German publication
Oldtimer Magazin, due in part to the influence of his friend and Classic Motorcycle Legends editor, Gordon Small. Almost 20 years later, his Model 7 again appeared in print; this time in RC, when Iain used the Dominator to transport his daughter to her wedding, and all wearing traditional Highland dress!
Iain’s ‘Seven’ came to me with a terminal clutch fault, a condition which had immobilised it for many months. I also agreed to sort any other faults that I might find, followed by a comprehensive service. A quick surgery in Iain’s shed diagnosed a locked-up clutch just as Iain had suspected, but the cause wasn’t immediately obvious. So Iain’s Model 7 was couriered to Fife and I began the
process of stripping the clutch.
Before the clutch becomes accessible, the footrests, brake lever and the primary-side exhaust system must first be removed. Iain had kindly supplied me with a manual, but it wasn’t until much later that I noticed the publication was for an ES2. However as we’ve already established, the Model 7 shares many parts with Norton’s best-selling single, so I wasn’t too concerned. But before I could inspect the clutch I would need to remove the outer primary cover, and, as many of you will have already guessed, this is a task fraught with torment!
The calamitous results of using modern silicone sealants on incontinent tinware are all too well catalogued. Suffice to say that several frustrating evenings spent with a rubber mallet and wooden wedges failed to budge the outer primary cover from its sticky, silicone grip. A sliding hammer inserted through the cover’s inspection hole was a last resort, but was hastily abandoned when it threatened to turn the cover inside out! And no suggestions or eureka solutions were offered by my curious fellow onlookers – apart from the usual sniggers of ‘perhaps you’ve left a screw in place?’
On the final session I was seriously contemplating the use of an angle grinder when I noticed a pool of oil below the cover – was it finally loose, I mused? Renewed tapping with a rubber mallet and periodic pulling and twisting was eventually rewarded by the most satisfying tearing sound as the outer and inner covers parted company.
So it was off with the clutch’s outer pressure plate, its three retaining bolts and clutch springs. This is followed by removing a unique outer steel band which once removed gives access to the clutch plates. As I began removing the individual plates I was already unearthing problems. Two steel plain plates had been fitted in succession, and as we seasoned RC fettlers all know, the common order should be plain / fibre / plain / fibre, etc. The steel plates were in serviceable condition and only required cleaning. The five fibre plate outer tangs however proved to be worn and would benefit from being filed smooth – a laborious but worthwhile task in rectifying clutch drag.
When I next removed the outer pushrod and its bearing cup, followed by the (second) inner gearbox pushrod, I thought I’d come across problem #2. Was a small inner ballbearing missing from between these two pushrods?
As I’ve come across this issue before, I reasoned that the lack of clutch adjustment could be caused by the omission of this ball bearing. So I inserted one, reassembled the clutch with a new set of clutch springs and bolts, but discovered the pressure plate wouldn’t fit because the outer pushrod was protruding too far. I realised a missing ball bearing wasn’t the solution after all – duh!
Frustratingly the manual was quite vague about clutch assembly, and moving on several paragraphs I turned my attention to the clutch adjustment (worm-thread) arm that lurks within the gearbox end cover – Norton aficionados will be familiar with this natty device…
On removing the cover I immediately noticed that the arm was positioned exceedingly high when compared to the manual’s illustration. It also appeared to be snagging with the gearbox’s inner shell whenever the handlebar lever was operated. And worse; both the cable’s end-adjusters were already fully extended, so lowering the arm by this method was no longer an option. But as soon as I lowered the clutch arm’s height, by screwing in the worm-thread mechanism, then normal clutch service resumed. I fiddled with the arm’s settings so that the cable would be the means of any future clutch adjustment – job done.
While inspecting the transmission, I’d noticed that both the primary and drive chains were extremely tight. However I couldn’t move the gearbox forwards or backwards to adjust either chain. This was because the upper gearbox adjusting bolt had a round head instead of a hex, and consequently it would not accept a spanner or socket. At the offending bolt’s threaded end, the fitment of a non-standard washer over its squared cam now prevented it from locking against the designated engine plate slot. Hence, when I attempted to remove the end nut, the bolt kept turning. I eventually managed to remove the bolt and nut using a Mole grip and spanner, but it was a lengthy, frustrating exercise. The offending part was replaced with the correct adjustment mechanism, which I’d fortunately unearthed in my Norton spares box. Now both the Model 7’s primary and drive chains could be properly adjusted.
RECOMMISSIONING
Bikes that have been laid up for a lengthy duration can suffer from common ailments. Predictably this can be an electrical fault, a fuelling or carburetion problem, or a mechanical failure of some description. The latter are usually the easiest to find and fix.
Basic ‘back to road’ tasks consist of cleaning and inspecting the carb/s; checking ignition timing, tappet and point clearances, engine compression and control cables. Thus while the engine was self-draining of oil I began checking the valve clearances. Both inlet tappets were tight and one exhaust tappet was loose – so all four were reset to their correct clearances. The magneto points were within a whisker of their 12-thou factory setting and only required a polish with fine emery paper. Ignition timing also proved to be spot-on, but a spark plug test revealed that the timing side plug wouldn’t spark. Swapping them confirmed that the plug was at fault and that both sets of HT cables and caps were working fine. A new set of spark plugs was ordered.
The Model 7’s pre-Monobloc carb has an accessible fuel chamber, but I decided to remove it for cleaning and inspection. I also replaced the manifold gasket (always worth doing). Clutch, front brake, throttle and choke cables were perfectly serviceable and only required lubricating. After removing the fuel reservoir cap, the float and valve cut-off heights were checked thoroughly. Some crud was removed from the float chamber basin and from the drain plug trap. Jets were removed and washed in thinners before being blown dry. I replaced any fibre washers and manifold gaskets before refitting the carb using a new set of locking washers.
Before I could replenish the engine oil I wanted to investigate a very ‘wet’ looking cylinder head. Once I’d removed the petrol tank and disconnected its oil pressure gauge, I discovered oil droplets on the Y-pipe that feeds the rockers. The pipe had quite obviously cracked across its soldered ‘Y’ joint – a common occurrence and usually caused by engine vibration. This leaking joint appeared to be the major cause of the engine’s unsightly oily head. However oil was also seeping from the four rocker spindle and tappet covers, so I ordered a set of top-end gaskets and copper sealing washers from RGM.
A tip for solder repairing a copper pipe is to first wash the damaged area in paint
thinners until spotlessly clean, then simply rough up the repair with a wire brush or emery paper until it appears bright and shiny. You can leave the repair overnight or dry it immediately with a hair dryer before attempting to apply heat and solder. It is also advisable to protect other localised solder joints (such as on a Y-joint) with asbestos tape or by placing large nuts over the joints (or banjos) to draw away unwanted heat. Much heat is required to sweat old and new solder into the repair, so applying just enough heat to make the solder run is important. Moving the flame on and off the repair will help to control the heat being applied. Once repaired, a worthwhile trick is to cut the oil pipe in half and join both ends with a piece of rubber hose to help insulate it from vibration.
Next the petrol tank was replaced and the oil tank filled with new engine oil. With fresh petrol and two new spark plugs I was ready to kick Iain’s Model 7 into life. Never having started a Model 7 before, the pre-ignition setup was largely guesswork. Tickle the carb; set the choke to fully on; bring the engine past TDC (easy with the low 6.7:1 compression) and kick without any throttle. The engine produced a ‘phut’, as it did on my second kick. On the third stroke, with a little tease of the throttle, she fired up! Immediately I peered into the oil tank to check for the rush of circulating oil. The softly burbling engine sounded marvellous and as circulating oil returned to the oil tank, the oil gauge began its steady climb, flagging that all was well with the bottom end. But suddenly, the engine began to billow smoke from its primary side exhaust. My initial reaction was concern, but as the engine sounded very healthy, I continued to warm it up.
Over time a laid-up engine can collect oil in its combustion chambers which lies in wait to surprise old fettlers like me. Before starting any laid-up motorcycle it is sage advice to always check the oil tank has sufficient oil. If not, drop the sump plug and decant the sump’s contents back into the oil tank. Run the engine until warm, checking that oil is returning to the oil tank, then at the earliest opportunity renew the engine oil. If an engine continues to smoke, it can be an indication of a worn valve guide, broken piston ring/s or a worn cylinder bore (check in this order). Iain’s Model 7 had stood unused for many years and I had to drain the engine’s sump of most of the oil tank’s content – a common result of long storage. I was hoping that any oil within the bores would eventually burn off, but only a road test would provide answers, so I kitted up.
TAKEN FOR A RIDE
The back of beyond is minutes from my door and, given the cloud of embarrassing blue smoke I knew to be dogging my heels, I felt very relieved to reach the cover of trees. Ten minutes into the ride and the 500 twin engine was chuffing admirably, its smooth progress winning over this cautious rider. As you purr along the exhaust note from the twin silencers is certainly muted, causing barely a ripple through the greenery. When I opened her up along the occasional straight she was still remarkably quiet; I did however keep one distracted eye on the puffing exhaust. Yet already I was thankful for the perceptible reduction in this old cruiser’s attempt to mask her position. And as I became comforted by the clearing rear view, I began to appreciate what a wonderful and charming ride the Model 7 really is.
The riding position is the epitome of the classic armchair pose, so perfect for daylong cruising. The Model 7’s controls and its few instruments are well-positioned; except perhaps for the tank-mounted oil pressure gauge – once an attractive instrument that time has now morphed into an illegible blancmange, demanding a sharp eye and a supple neck. The Norton gearbox and the super-light clutch (ahem) seduce the rider with their silky-smooth operation. No doubt the agreeable transmission is further enhanced by the clutch’s rubber shock absorber, although on two separate occasions I couldn’t select top gear. Perhaps this was the result of a lazy return spring or just pilot error. Whatever, a mere foot-tap on the lever restored normality, and not once was there a hint of clutch-slip, despite the ‘one digit’ action clutch.
In reality, the buzz and glide of Norton’s post-war twin was quite becalming – until the bike crashed through a hidden chasm that was masquerading as a pothole. The rear suspension is positively rigid and any ‘plunging’ is quickly followed by the rider being rudely ejected from the saddle! Rear suspension-wise there is apparently some perceptible movement, or so I was assured by a friend strategically positioned to observe my vigorous bouncing up and down on the Seven’s rear end. At speeds of anything over 20mph, riders of this machine would be well-advised to scan for incoming potholes. Otherwise the handling is actually very good, as one would expect from a Roadholder Norton. With almost thirty horses to play with, this early Dommi is a hint of pleasures to come. Not as aggressive or sure-footed as its later featherbed brethren, it is nevertheless an excellent steed for making smooth progress.
The 497cc Model 7 has a fairly long stroke (66 by 72.6mm) and is certainly nippier and smoother than the equivalent capacity single of its day. A bewitching little motorcycle, it soon gets under the skin; as no sooner have you parked up, than it’s time to get back on and play again. The inherited ES2 frame provides a solid and dependable ride and it’s a similar story with the Roadholder forks. Press plaudits at the time reassured prospective buyers by saying that ‘the Model 7 sacrifices some comfort for excellent road-holding and precise steering’. Yes, the front-end ‘bangs’ through potholes while the rear can feel like Pompeii revisited on the odd occasion, but the Norton steers well and is never shaken from its line. Potholes aside, I found it to be a comfortable, everyday machine that is perfectly capable in modern traffic.
Both the front and back seven-inch drum brakes require a bit of stomp but, in combination, haul up this 66 year-old machine without drama. The front brake was nearing the end of its service life and perhaps a new pair of shoes would add some appreciated urgency in the braking department. In common with many British classics, the back brake was the better performer.
Fifty is nifty on the Model 7, although I did wind her up to a brief 70mph on one occasion, just to observe how harsh the engine might prove around its upper limits. But I’m glad to report that the ride was relatively smooth in comparison to some larger vertical twins I’ve ridden. Around town the whole package is light and responsive and easily weaves a path through the maddest of rush-hour traffic. Another pleasant surprise of the city ride was the number of grins and thumbs-up this old Seven received from attentive drivers and pedestrians.
Step back and the early 1950s Model 7 Dominator looks a very attractive motorcycle. And in common with all Nortons it has a racy and predatory look, emphasised by the generous and scalloped petrol tank which looks splendid in Norton racing silver and black. The beefy engine, deeply profiled mudguards, low plunger frame, single saddle and twin cigar-shaped silencers are typical styling cues of the period – yet somehow the Model 7 Dominator looks different.
My last job was to fit a Norvil sidestand that Editor Westworth had recommended to Iain. An excellent piece of kit, this item highlights a back-breaking problem that unfortunately blights this old Norton’s otherwise excellent
reputation: its centrestand, or I should say ‘offcentrestand’. The Model 7 is surely one of the most awkward motorcycles the poor (young or old) classic enthusiast has ever had the misfortune to wrestle onto its centrestand. No lifting grips or handles are evident, and the extreme effort is shouldered solely by one’s arms and back. It’s far from a well-designed lifting device and I would suggest that the fitting of a sidestand – certainly for those of us who value our backs – is an absolute must!
I returned the Model 7 to Iain in very fine fettle and I’m sure it will continue to thrill him for many, many years to come, such is the quality build and excellent engineering that is intrinsic to Norton’s first twin. But just so you know, dear readers, I’m first in the queue.