For a while, the plunger cammy Norton fell out of favour with fast lads who preferred the featherbed frame. But Rowena Hoseason reckons that any 500 single which will take you to the ton is worth a second chance…
For a while, the plunger cammy Norton fell out of favour with fast lads who preferred the featherbed frame. But Rowena Hoseason reckons that any 500 single which will take you to the ton is worth a second chance…
When people talk about Norton’s cammy singles they typically mention the Manx first and the International… well, eventually, maybe, as a bit of an afterthought. Hardly fair, seeing as the International came first and the Manx model popped up post-war. The Inter was the 1930s race-bred roadster equivalent of the works overhead cam competitors.
Joe Craig and Arthur Carroll drew up the new Norton cammy engine for the 1930 season, to cure some of the groundbreaking CS1’s idiosyncrasies. The CS1 was an impressive engine, but it was technically tricky to keep in tune and riders found it tough to extract its peak performance. The Inter was a smaller machine overall, with a shorter wheelbase and lower riding position which favoured the vintage style of ‘lean out’ cornering, knees gripping the tank to stay in the saddle.
The new model paved the way for the cammy Norton to become a clubman’s racer rather than a pure works machine – it was perfectly possible for Inter owners to swap a valve or a piston without an entire team of mechanics. Inevitably the boys of Bracebridge Street offered private customers the option to upgrade their Inters with all manner of competition-spec components. In the mid- 1930s you could specify an Inter in ‘Manx GP’ trim, bristling with optional extras. After WW2, things became clearer with the launch of the customer double-knocker Manx model in 1949, while the Inter stayed available with its sohc top end. That doesn’t stop today’s sellers misdescribing an overpriced cammy single as a Manx when it is in fact an Inter, of course…
BACK IN THE DAY
Even among the actual Internationals, there’s a clear demarcation of desirable incarnations. Most folk feel that the truly unapproachable Norton is equipped with a featherbed frame, so the 1953-onwards version of the Inter, with all-alloy engine and laid-down gearbox, is usually the one which hogs the limelight. At the other end of the spectrum lies the simplicity of the Inter’s original iteration with rigid rear end and girder forks; a genuinely vintage experience from the 1930s. The final featherbed Inters might be the most powerful of the bunch and are blessed with the best handling of their era, but the early Inters are pretty frisky when the engine comes on song. Both types sell for seriously big bucks.
Then there’s the awkward interim model. The Inter was reintroduced after WW2 for the 1947 Clubman’s TT, where both 350 and 500 took top honours. This bike was little more than a refreshed version of the pre-war racer, but the customer machine which followed for 1949 was a more pragmatic proposition. For the first time, the public was offered a cammy engine in a chassis with suspension at both ends – but the ‘garden gate’ frame with tele forks and plunger suspension did not meet with universal approval…
The pre-war rigid bikes’ short wheelbase and low centre of gravity gave them responsive handling and instinctive steering. ‘Plunger suspension,’ observed Don Morley, who owned several Inters over the years, ‘especially if combined with tele forks, raises this level, adding considerably to the overall weight to ruin the entire equation. Indeed, these Inters suffer from stodgy and decidedly unsporting handling.’ He thought the 1949 incarnation of the Inter was ‘beautiful-looking but ultra-heavy and evil-handling.’
Historian Roy Bacon agreed. He thought the post-war Inter was ‘wonderful to look at’, but ‘it was no road machine. It rattled, it leaked oil and the cam timing battled with the silencer to hold the road performance down to around 85mph for the 500. The 350 was slower, having to drag along virtually the same weight, and thus its acceleration suffered badly.’
Even so, if you fitted a free-breathing pipe, then ‘a good 500 could make a memorable experience.’ Fitted with a Brooklands can, a plunger-framed 500 in a pre-war state of tune was timed at 97mph, and Bacon reckoned that ‘the engine, coupled to a close-ratio gearbox, had deep-down stamina. The plunger frame called for a firm hand and could roll at higher speeds, but would always work with a rider to keep him out of trouble and get him through a corner.’
Fast riders certainly could make the most of the racing version of Norton’s plunger frame. ‘It made the bikes much more comfortable to ride in long races like the TT,’ according to the firm’s works rider Freddie Frith. And indeed, Frith clocked the first ever 90mph lap of the TT circuit in 1937 on a cammy single in a preproduction plunger frame. However, as Jim Reynolds once observed, ‘action pictures of the time suggest a very physical high-speed wrestling match!’
These opinions explain why the plunger Inters have traditionally been less soughtafter than their siblings, and why their values haven’t risen quite so stratospherically. Although the Model 30 (490cc) and Model 40 (348cc) were the top of Norton’s range for 1949, those times were pretty tough. Gone were the gloriously high compression ratios of the late 1930s, when works racers ran 12:1 on exotic fuels – the 1949 Inters were fitted with compression plates to cope with poor quality, 72-octane pool petrol.
While the works bikes were still gussied up with trick bits, the road-going Inter specification was a bit less special than it used to be and shared many more components with the ohv roadsters. The sohc iron engine
retained its ribbed crankcase with built-up crankshaft, duplex gear oil pump, exposed hairpin valve springs surrounded by oil feeds, adjusters and breathers, with petrol provided via a TT carb.
A three-spring multi-plate clutch transmitted drive to Norton’s four-speed positive-stop gearbox, now converted to foot change. The chain-drive magdyno was mounted behind the cylinder, ahead of the handsome, wraparound oil tank. The petrol tank lost its delicious scalloped edges but kept the cutaway to accommodate the carb.
The garden gate frame is similar to the one used on the ohv ES2 single, adapted to suit the cammy engine and fuel/oil tanks. While the Roadholder forks at the front end were an undoubted improvement over Norton’s Webb-type girders, the Inter lost its lightweight pre-war mudguards and was weighed down with a set of standard guards. The Inter was given different tyres to the ES2, and swapped from a 3.25 rear section to 3.50 for 1951.
Although the roadtests of the time overflow with gushing appreciation of the post-war plunger Inter, you can tell that it was a tricky creature to tame. ‘A trace of clutch drag made low speed gear changing slightly heavy,’ said
The Motor Cycle, ‘and it was not usual to obtain an absolutely clean change from bottom to second gears.’ They felt that the 32-inch saddle was pretty high, while the 29-inch wide handlebars were unusually wide.
Although this gave it ‘the feel of a big machine,’ the Inter was considered extremely agile, and its braking was flat-out fabulous: 25ft from 30mph is impressive by any standard. Motor Cycling noted that the rear springing felt quite hard in action, but certainly aided stability: ‘road-menders’ vicious cross-gullies could be tackled without gripeasing.’ Both publications suggested that the Inter was suited only to experienced, hard riders – and Motor Cycling had the decency to note that their bike was equipped with a special silencer: the customer machine would be quieter and somewhat… slower.
The reintroduced Inter had certainly lost some of the pre-war model’s sparkle, but it was only intended to be a stop-gap, while Joe Craig and his gang got to grips with the Manx motor and an all-alloy sohc engine which would slot into the featherbed frame from 1953. Even so, some technical trickery kept the plunger Inter competitive on the Island, where it claimed three wins in 1949, 1950 and 1951 in the Senior Clubman’s TT.
The plunger Inter was also a practical proposition for the man (or woman) in the street. Before WW2, intrepid traveller Theresa Wallach secured her gold star at Brooklands on a 350 Inter, lapping at over 100mph. Yes, I did type that right. A 350. At 101.64mph. OK, so Wallach chose her motorcycle wisely – the bike was hired (for £5) from legendary tuner Francis Beart – but her achievement is all the more mighty when you consider that it lashed down with rain that day…
The post-war version might not’ve been up to matching that feat, but instead a tele / plunger Inter carried Wallach on an epic adventure across America. For nearly three years, she worked her away around the USA, Mexico and Canada, maintaining her machine as she clocked up over 30,000 miles.
So take heart if you quake at the idea of setting up the Inter’s top end, with its cam driven via that handsome two-piece bevel shaft and an Oldham coupling. Don Morley suggested that any reasonably competent spannerman shouldn’t feel too intimidated by the Inter engine. It ‘need hold no great terrors,
for they are remarkably simple,’ he said.
Morley found the Inter motor to be much the same as Norton’s ohv singles ‘with a few extra but minor complications, like a need to shim the upper and lower bevel gears to obtain perfect mesh. There is little to worry about, given a source of shims, some common sense and a modicum of patience which are all needed for assembling, dismantling and reassembling the bevel gear housings as often as it takes until the clearances are right.’
The main thing with the cammy motor is getting to know it, so you can prevent any little issues developing into major aggravations. For instance, the smalldiameter feed to the valve guides – especially on the exhaust side – can get choked with cacarbon.bo. Modernode ridersdes may also want to consider carefully the merits m of the raceoriented close-ratio gea arbox which features a vast gap between firs t and second. Don Morley reckoned that the 500’s ‘wonderfully free-revving’ engin e with its ‘oodles of usable torque’ works w better with a wider-spaced gea ar set from an ES2: ‘less of a pain to use o n today’s roads.’
And there is every chance that if you buy a plunger Inter you will end up riding it – this is another motorcycle which has found more favour as a classic than it did during its initial outing. It may be heavier and slightly slower than the flyweight pre-war machines, but the Roadholder forks and seven-inch stopper are much more suited to 21st century traffic than 1930s girders. You could remove the compression plate and give the performance a bit of a bump… or leave it in situ and enjoy kicking over a big single without it snapping at your ankle.
Likewise, the plunger Inter is both lower and slimmer than the featherbed which followed it. (Nor is the featherbed frame of the International quite the same as the one with which the twin-cam Manx was equipped). If you want an exotic Norton which is beautifully balanced and easy to manoeuvre at low speeds – but which won’t shatter your spine as you rumble over every road ridge – then the garden gate variety has an awful lot going for it.
AN INTER IN ACTION
Rowan Bond in Australia didn’t need too much convincing. He fell in love with cammy Nortons while watching them race in the 1970s, so when the opportunity arose to secure (most of ) one in 1983 he snapped it up. His 1949 Model 30 was incomplete and very rusty. ‘I found the rolling chassis and gearbox on a dump; the engine had been used in a speedway car.’ Assembling an actual motorcycle involved sourcing the missing components, replacing the ones which were beyond recovery, and building up the resulting jigsaw puzzle – and it took a while before Rowan could really get to grips with the project. Over seven years between 1993 and 2000, Rowan did the majority of the work himself, calling in expert assistance for crucial tasks.
‘My frame was broken so the front downtube was sleeved and pinned. The frame was quite horribly bent out of shape from lying in the dump with things tossed on top of it, so there was quite a bit of work straightening it for use. While it’s not in the featherbed class of handling, it does handle and ride very well. The Inter sprung heel is, I believe, much better than the same fitted to the ES2, due to the different dimensions. The suspension is much more compliant and the chain tension is maintained much better.
‘When I built my motor, I was assisted by an old friend who’s now unfortunately no longer with us. Garth was quite a whiz with bevel bikes, especially Ducatis and Nortons. He was quite experienced at putting them together, even though he used to make jokes about emptying the oil out of your right boot every 100 miles or so. As a result, my engine is almost oil-tight with only a few spots of oil from the cambox after a good 60 mile thrash at highway speed.
‘We used Three Bond sealant (the white one) wherever possible. The bevel housings have never leaked a drop. We made the cambox as oil-tight as possible by making sure that the circular alloy muff surrounding the cams is undamaged. Mine was broken, so had to be re-welded.
‘I also took great care in ensuring the sections of the rockers which act on the felt wipers were perfect and polished to a good finish. We also discarded the felt wipers. I fashioned some appropriately-sized neoprene cork sheet (left over from the discarded part of a car tappet cover gasket), which was wrapped on both sides by a red silicone sheet material of about 1.5mm thick. This material is extremely expensive and used in the mining industry. As we had lots of mines around our area, I was able to get a small offcut which would be big enough to do all the Inters left in the world!
‘ The sheet was bent in a U shape around the neoprene cork so it ended up with the two loose ends pressing on the rockers. I shaved both ends into a sharp blade in the same manner as a windscreen wiper and then put it all together. These wipers were used top and bottom and have worked spectacularly well for almost 20 years at keeping the vast majority of the oil in. I use mineral oil in the motor, normally straight 50, and use the highest octane fuel I can get, and always ensure it is fresh.’
In keeping with the intended purpose of the International, Rowan went for a highperformance spec; Manx cams, high-comp piston, TT carb, close-ratio gearbox and a tacho. But there are downsides to fast living. ‘When I first restored the Inter, I didn’t have the nut on the end of the camshaft tight enough, and it came loose, allowing the cams to move, and I bent an exhaust valve.’
Then in 2002, ‘the piston melted due to poor quality fuel. The bike was pinking badly, and lost considerable power. While trying to get home, I played continually with the advance/retard and fuelling as much as I could, but 60km from home the motor partially seized. It also broke a couple of teeth off the bottom bevels, which was quite a disaster. I sourced some bevels and a new piston, and got it back on the road in a few months.
‘After I trashed that piston, I went for a lower compression piston made locally here in Australia. Whilst ultimately the performance is not quite as good as before, it is much easier to live with. It has not let me down since.’ So what’s it like, living with a legend? ‘Starting is easy hot or cold,’ says Rowan. ‘I had the magneto refurbished at restoration, which helps significantly. Cold starting procedure is to tickle the TT carb until it floods, and close the air slide. After that retard the ignition about a quarter from full advance and give the bike a smooth but hefty kick. It will start on the first or second kick usually, even if it has not been used for some time. Fresh fuel is important. If you give it too much advance, it will give you a fearsome kickback, but just retard it a little from that point and away it will go… ignoring the pain in your foot and ankle of course!
‘ The close ratio box is not much fun around town or two-up. First gear is quite high, and there is a gap to second (It has the fabled 20/22 tooth combination second gear fitted) with the top three ratios quite close together. It is magnificent going up and down through the gears on a good windy road though. I hate riding two-up especially around town as the combination of the ratios, the TT carb and Manx cams makes it an interesting progression between traffic lights.
‘ The clutch seems to put up with the punishment of town riding quite well but does start to complain, being grabby after a while. Luckily, I live out of town so can stretch the bike’s legs almost immediately. It’s an absolute joy to ride once you attain about 40mph.
‘As for the brakes, well, they’re about what you would reckon for a 1949 bike. I did the best I could with them and used quite soft, organic linings which were done for me at a local brake specialist. They wear quickly but have nice feel and are quite powerful. Powerful enough to compress the forks significantly when strong braking is necessary, and the back wheel can be locked with relative ease. Having said that, it is prudent to ride with some anticipation of what is going on in front of you to make sure you can stop in time.’
So even though the ‘experts’ might not think so much of the plunger International, this owner definitely believes his effort and expense were ‘entirely worth it. I have a nice collection of bikes and the Inter is my standout favourite both to look at and to ride.
‘It’s quite rightly a classic ride, especially if you restore it yourself. On back roads and when it comes on the cam it makes a great sound, and has the performance to match.’