1963 Royal Enfield Mk1 Interceptor
Engine: 747cc air-cooled parallel twin, 71.5mm x 93mm bore and stroke, 8.5:1 compression ratio, 55hp @ 6,000rpm (claimed)
Top speed: 115mph (est.)
Weight (dry): 410lb (186kg)
Fuel capacity: 3gal (11.4ltr)
When I was in high school 45 years ago, there was an older kid who was unremarkable except that he owned two Royal Enfield Interceptors. That made him cooler than cool, because the merely cool rest of us rode more common British bikes or maybe something Japanese.
Greg Lawless bought this 1963 Interceptor for $500 in May 1973 as a college graduation present for himself. I suspect he experienced an immediate spike in his coolness. Over the last 42 years — including six moves involving three states — Greg’s put lots of miles on it and made many memories with it. Though his current collection includes 26 motorcycles, Greg says the Interceptor is the last bike he’d sell.
A little background
Royal Enfield was founded in the 1890s in Redditch, England, (just south of Birmingham) by two bicycle manufacturers who also made interchangeable gun parts for the Royal Small Arms factory in Enfield. For its logo, the new company chose an artillery field gun.
Royal Enfield’s first motorized bicycle, built in 1901, was followed by models incorporating such innovative features as crankcases with integral oil tanks (1903) and rubber “Cush Hub” drives to reduce chain snatch (1912). Royal Enfields were the first English production motorcycles with dry-sump lubrication systems and gear-type oil pumps (1913). The “Super 5” model, launched in 1961, was the first British production motorcycle with a 5-speed gearbox.
In 1948, the company launched the model that was to become synonymous with Royal Enfield: the redesigned overhead valve single-cylinder Bullet. This robust and versatile machine was utilitarian but also excelled as a competition motorcycle, especially in trials events.
Although Enfield ceased U.K. production of motorcycles in June 1970 to focus on military contracts (Royal Enfield had been making aircraft and guided missile components as well as motorcycles), Enfield Bullets are still being made in India, making Royal Enfields the longest continually produced motorcycles in the world.
Though never as large as BSA, Triumph or Norton, Royal Enfield had an advantage: Its small senior management team included enthusiastic motorcyclists and former competitors who knew what riders wanted. They fostered new ideas and encouraged the introduction of models known for innovative design and robust construction.
The Big Twins
Royal Enfield launched its first parallel (or vertical) twin in 1948, with a 64mm by 77mm bore and stroke and 25 horsepower. The basic design of the 500 Twin was to be carried through the subsequent, larger displacement models and included a long stroke for low-end power, a one-piece cast iron crankshaft, and separate cast iron barrels with aluminum heads and short alloy pushrods riding on a pair of camshafts.
Advanced features for the time included a full-flow oil filter and semi-unit construction, with the gearbox bolted to the rear of the engine. The frame was welded steel with a single downtube attached to the front of the engine-gearbox unit, which acted as a stressed member. The swingarm rear suspension was a first for a parallel twin.
In 1953 the Meteor 700 was introduced as Britain’s biggest parallel twin — BSA and Triumph offered only 650s at the time. The 36 horsepower, 693cc Meteor was primarily intended to meet the needs of the sidecar market. It was essentially a “Double-Bullet,” each cylinder having the same bore (70mm) and stroke (90mm) — and pistons — as the 350cc single.
The Super Meteor followed in 1955 as a more sporting Meteor. Made in response to U.S. market demands for more power, it made 40 horsepower and was the first Royal Enfield capable of 100mph. The 51 horsepower Constellation followed in 1958 with hotter cams, a single 10TT9 Amal carb and siamesed exhaust.
In 1961 the factory made a limited run of Constellation-based specials for the U.S. market, the 700 Interceptor. Set up for offroad enduro-style events, they weren’t popular and most of the approximately 160 bikes were retrofitted by dealers with aftermarket horns, mirrors and lights and sold for road use.
In late 1962, Royal Enfield bored and stroked the Constellation’s engine to 736cc to launch the 750 Interceptor Mk1. It went head-to-head in the showrooms with the new Norton Atlas 750 and, like the Norton, it was aimed squarely at the U.S. market. Both bikes were offered stateside before they became available in the U.K.
Enfield dynamically balanced its big twin engines, reducing vibration compared to large displacement bikes made by competitors, who used static balancing. The long-stroke design produced abundant torque from low revs, making the bikes very tractable and capable of impressive acceleration. On the downside, the separate barrels and heads meant that the engines — being stressed members — tended to flex, which, combined with poor crankcase venting, led to the bikes having a reputation for leaking oil, hence the nickname “Royal Oilfield.”
The Interceptor was upgraded in 1964 with a second petcock, float bowls on both Amal Monoblocs, magnetic instruments, Girling shocks, an auto-advance magneto, hotter “R” (Supersport) cams, and one less tooth on the countershaft sprocket for better acceleration. In the U.S., the 1964 model was known as the TT Interceptor. The single-carb Custom with standard cams was added in 1965, and the 1966 GT with twin carbs and sport cams gave three Mk1 models available that year.
The Interceptor Mk1a was introduced in late 1966. Produced at new facilities at Bradford-on-Avon, it featured twin Amal concentric carbs, coil ignition and better engine breathing. Two models differing only in cosmetics were offered in the U.S.: The Road Scrambler TT7 (upswept pipes, chrome tank and exposed chrome shock springs) and the Road Racer GP7 (flat pipes, painted tank and shrouded shocks, more like the old Mk1).
Royal Enfield produced its last twin, the Interceptor Mk2 (aka Series 2), from 1968 to 1970. The engine was redesigned to be wet-sump, the contact points were relocated in the timing cover, and Norton front forks and front brake were used. The Mk2 bikes leaked less oil than the Mk1 versions, but were heavier and slower. The factory had plans for an 800cc Interceptor Mk3 successor, but never put it into production, although prototypes were made and road tested.
The Royal Enfield Interceptor was considered one of the Superbikes of the Sixties. When a Mk1 ran a 13.8-second quarter-mile, Cycle World editors proclaimed it the quickest stock production bike they had ever tested. In addition, a bike powered by two Royal Enfield Interceptor engines was the first non-streamlined motorcycle to exceed 200mph, hitting 203.16 mph at Bonneville in 1970.
Greg Lawless’ 1963 Mk1 Interceptor was one of approximately 250 built that year and one of 979 Mk1s produced between 1962 and 1966. There were two variants of the Mk1 for the U.S. market — Greg’s is the second type with a polished alloy instrument nacelle (not black) and a polished alloy wing knob for the steering damper (rather than a big black round knob). Unlike the U.S. models, the Mk1s sold in the U.K. and the rest of the world had bigger gas tanks, twin-sided 6-inch front brakes and shorter swingarms and wheelbase.
The 1962-1963 Mk1 had twin 1-1/8-inch Amal Monoblocs sharing one float bowl, a Lucas K2F manual-advance magneto, a 6-volt alternator and a 4-speed Albion gearbox with a neutral finder. The gas tank had a single petcock (there was no reserve), and a Smiths chronometric speedometer and tachometer were standard.
In the 1980s, Greg rebuilt the top end with the help of J.B. “Bernie” Nicholson of Modern Motorcycle Mechanics fame in Saskatchewan, Canada. Oversize Hepolite pistons for 736cc engines were impossible to find, so Bernie provided 0.060-inch-oversize 700cc Constellation pistons, which are 0.020-inch oversize for a 736cc engine. Those pistons are still in the bike.
Greg undertook a major restoration of the bike in 2010, the end goal being a practical and rideable classic machine. He replaced the notoriously bad stock 7-inch single-leading-shoe front brake with a twin-leading-shoe unit from a modern Indian Bullet. He says it’s a big improvement, but planning one’s stops is still recommended.
Greg rebuilt the engine, giving it new valves and seats, new piston rings and new bottom-end main bearings and connecting rod bearings. It also got R-type cams, and a 19-tooth countershaft sprocket replaced the stock 20-tooth item. A Bob Newby Racing clutch and belt drive kit took care of clutch problems and primary case oil leaks. The stock Amal Monoblocs were replaced with modern 30mm Amal Premier Concentrics, and a modern BTH magneto replaced the Lucas K2F unit. This fixed an old problem of having up to 10 degrees of ignition timing variation between cylinders while also providing an improved spark advance curve. Electrics went from 6-volt positive ground to 12-volt negative ground, and with a Sparx single-phase alternator and solid-state rectifier/regulator/capacitor it can run without a battery.
Greg installed a Mk2 Interceptor-type oil cooler and carried out a few other modifications to improve engine lubrication. To address the lack of engine rigidity due to the engine’s separate cylinder barrels and heads, Greg fabricated a stainless-steel head-steady plate that significantly reduces engine flex and in the process improves oil-tightness.
Originally Chinese Red, Greg repainted the bike in HiFi Blue (a stock color for 1964) — a three-stage application with silver base, blue midcoat, hand-painted gold pinstripes on the tank, and a clear topcoat over stripes and decal. Finally, the frame, swingarm, headlight housing, fork covers, taillight housing, and miscellaneous black items were powder coated.
It’s easy for Greg to compare his Interceptor to other vertical twins — his current stable includes a 1961 Norton Manxman, a 1962/70 Greeves Triumph 500, a 1968 BSA Firebird Scrambler, a 1975/72 Rickman Triumph CR650 and a 1974 Norton 850 Commando Interstate.
Greg says the Interceptor’s engine is wonderfully balanced, and even with the heavier oversize pistons, he says it is the smoothest 360-degree vertical twin without a balance shaft that he has ridden. It has gobs of torque and pulls stronger at low rpm than any vertical twin he has ridden except his Norton Commando.
One advantage of the engine’s separate barrels and heads is cooler running and easier access for maintenance and, because the gearbox bolts directly to the back of the engine, variation in primary chain tension is minimized. The integral oil tank means fewer external oil lines (and fewer leaks), and the engine design allows for swapping cams without disassembling the crankcase.
The neutral finder lever on the gearbox is also a nice feature. The transmission can be a little agricultural in its shifting, and the stock clutch tends to drag, so it’s nice to be able to heel-tap the neutral finder when coming to a stop in any gear (except first) to find neutral.
On the road
Greg says the bike is nimble, yet also stable at high speed thanks to the longer U.S.-spec swingarm. “It’s the first bike I went over 100mph on,” Greg says, “in fact 110mph two-up in 1973. Only scared my rider — well, me a little.”
Maintenance is relatively easy. One bolt retains the outer primary cover and there’s good access to the spark plugs, rocker arms and magneto points. The oil drain plug is on the side of the engine case and the somewhat effective felt oil filter is easy to clean.
Support groups include a Royal Enfield owners club and a website specifically about Interceptors. Two excellent long-standing sources of parts and advice are Hitchcocks Motorcycles and Burton Bike Bits. Allan Hitchcock, in particular, has a reputation for being a tireless champion of the marque — not only keeping new-old-stock and pattern parts but also fabricating special bits and engineering new, improved solutions to old Enfield shortcomings.
Greg and his Interceptor are now in their fifth decade together, longer than many marriages last. Indeed, elevating the bike to its current lovely condition has been a labor of love. It has paid off though — the Enfield looks stunning and runs strong. Exactly what you’d expect from a marque whose motto was: “Made Like a Gun.” Pretty cool, huh? MC
The Final Chapter: The Rickman Interceptor
The final chapter of the Interceptor story includes two specials not built by Royal Enfield, but based on the Mk2. In 1968, Floyd Clymer, Royal Enfield’s Western U.S. distributor, made plans to market a line of motorcycles in the U.S. under the Indian name. He intended to put Mk2 Interceptor engines into a chassis built by Leo Tartarini of Italjet in Bologna, Italy. The first few Indian Enfields were launched in 1969, but Clymer passed away in January 1970 and the project floundered. The unused Interceptor engines ended up in a warehouse, needing a new home. Enter the Rickman brothers, renowned for their exceptionally well-made frames.
Don and Derek Rickman’s Interceptor-powered special weighed 60 pounds less than a standard Mk2 and featured their fabled nickel-plated chrome-moly duplex “Metisse” frame with swingarm pivot chain adjustment, Ceriani forks, Lockheed disk brakes front and rear, and a fiberglass tank, seat and fenders. Between April 1970 and January 1972, approximately 130-137 Rickman Enfields were produced, making them rare and highly sought-after today. — Corey Levenson
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