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Cream Machine: 1930 “Ivory” Calthorpe

Clive Curry needed a motorcycle built before 1936 for a regularity run. He found one in a 1930 Ivory Calthorpe.

by Robert Smith

1930 “Ivory” Calthorpe 350

Engine: 348cc air-cooled OHV single with twin exhaust ports, 74mm x 81mm bore and stroke
Top Speed: 67mph (approx.)
Carburetion: Single Amac TT (stock), Amal 276 fitted
Transmission: Burman 3-speed gearbox, handshift, chain final drive
Electrics: 6v, BT-H magneto
Frame: Dual downtube cradle frame
Suspension: Druid girder fork front, rigid rear
Brakes: 6in internal expanding drum front and rear
Tires: 26 x 3.25in front and rear
Weight: 320lb (est.)
Fuel Capacity: 2.25gal Imperial (2.7gal. U.S.)
Price Then: £47 (1930)

Clive Curry had always wanted to participate in the Durban-Johannesburg trial, a regularity run in his native South Africa. But he lacked one essential ingredient: a motorcycle built before 1936, as the rules stipulate.

The “DJ” as it’s known, is no longer a race as it was from 1913 to 1936. Instead, riders must arrive at each checkpoint as close as possible to a specified time, in the style of the modern Motogiro d’Italia or the resurrected Milano-Taranto run. This is the story of how Curry acquired what is perhaps the perfect motorcycle for the DJ: a 1930 “Ivory” Calthorpe 350.

The Calthorpe

In taking any product to market, one of the most powerful ways to boost sales or justify a higher price is to offer a Unique Selling Preposition — or USP. It’s the feature or benefit that makes your product or service stand out from the crowd. For example, if you’re the car rental company that will “pick you up” from your home or office, that’s your USP. For many years, Royal Enfield’s neutral-finder gearbox was an important USP.

If you were a maker of mid-size motorcycles in Britain in the late 1920s, it was a crowded marketplace. Almost every maker offered an overhead-valve 4-stroke 350cc single. But because of the British industry’s reliance on outsourced components, the brands were often more-or-less interchangeable. Your new bike probably had a BT-H or Lucas magneto, Amac or Brown & Barlow carburetor, Burman or Albion gearbox and so on. The front fork was probably Druid or Webb. Even the engine might have been sourced from JAP, Blackburne, Matchless or Rudge. How does a company make its product distinctive?

From 1929 to the late 1930s, while most British motorcycles were finished in black, maker Calthorpe painted its bikes an off-white color they called Ivory. They were certainly distinctive, but were they any better than the herd? Was the color a USP — or just a gimmick?

Before Ivory

Like most British motorcycle makers, Calthorpe got its start making bicycles and bicycle components. George William Hands, though of British descent, was born in Bridgeport, Connecticut, but served his apprenticeship as a machinist in Birmingham, England. Partnering with one Arthur Cake, Hands formed Bard Cycles in 1895, but the company was insolvent by 1899.

By 1905, Hands had formed the Minstrel and Rea Cycle Co., which likewise produced bicycles and seems to have been more successful. Perhaps as a sign of what was to come, Minstrel and Rea cycles were particularly noted for the quality of their finish.

Hands also introduced Calthorpe automobiles in the early oughts, using proprietary engines from White and Poppe. So it followed that when the first Calthorpe motorcycle appeared in 1909, it used a 3-1/2 horsepower White and Poppe sidevalve engine. The single-speed, belt drive machine featured an innovative safety aid: When the front brake lever was applied, it also cut the output from the magneto, thereby adding engine braking to assist retardation.

Between 1910 and 1924, Calthorpe continued development of its motorcycle range still using proprietary engines, mostly from Precision, JAP, Blackburne, Villiers, and Pearson & Coles (“Peco”). It was for the 1925 season that Calthorpe introduced its own engine, an upright 350cc OHV single of mostly conventional design, but it featured the 74mm x 81mm bore and stroke that would stay with the 350cc single until 1936. Launched as the “Sports” model, it featured enclosed rockers with automatic lubrication (though the valves were still exposed) and an automatic recirculating oiling system for the engine’s double-roller-bearing big end. Primary and final drive were by enclosed chain through a Burman 3-speed gearbox. Sparks were courtesy of a CAV magneto, and carburetion by dual-lever Brown & Barlow.

The 350cc “3-1/2hp” Sports was an instant success, such that for 1926 a “Super Sports” model was also available with Amac TT carburetor, BT-H magneto and “tuned to be capable of 75mph.” Both models continued for 1927, but now both fitted with the Amac TT and BT-H mag. A smart octagonal streamlined sidecar was also available.

Image by Robert Smith

The lever mounted to the end of the bar is the clutch, while the smaller lever is the compression release.

For 1928, the two 350s were re-positioned as the “Popular” and “Sport,” but with similar specifications. The first Ivory Calthorpe appeared in 1929, an updated Sport (now called the “Super”), with “domed racing piston” and a twin port head. (The Popular continued in black finish.) The Ivory could be ordered with a speedometer, Lucas or Miller lighting system and “specially tuned racing engine.”

By this time, Calthorpe had dropped all its other models and relaunched the 350 Ivory in 1930 with a revised “sloper” engine angled forward in the frame as was the fashion of the time. The engine’s bottom end now used ball- and roller-bearings throughout, abandoning the timing side bronze bush. An oil reservoir was cast into the front of the crankcase, and a patented oil feed to the engine used the timing gears as an oil pump. The cylinder head and the front fork were revised, the latter getting a new center spring.

The Ivory continued for 1931, but with a new 4-speed gearbox made under license from Albion. And for 1932, the 350 (now called “Ivory Junior”) was joined by a 250cc 2-stroke Ivory Minor and 500cc Ivory Major. In 1933, Calthorpe announced its “one model” strategy, that being the 500cc Ivory. The 250 returned in 1934 (as a 4-stroke) and the 350 reappeared for 1935. The 1936 range featured fully enclosed valves and included special competition versions of the 350 and 500; but these were still based on the 1930 engine, which was reaching its development limits (especially the 500), and reliability suffered.

Motor Cycling magazine tested the 1937 Ivory Calthorpe 350 “de luxe,” (now with 71mm x 86mm bore and stroke). They found that starting required “a little more effort than usual,” but noted that “Idling was excellent and particularly smooth. Indeed smoothness was a characteristic of the engine throughout the rev range.” On the open road, “the Calthorpe handles like a 250” with a marked “self-centering effect” to the steering, and when cornering “it seems automatically to adjust itself to the correct angle and hold itself there regardless of the road surface … At high cruising speeds, the handling is excellent and requires no effort.”

They found the Calthorpe would cruise comfortably “between 50 and 60mph and recorded a one-way top speed of 67mph. Acceleration from a standing start “was almost as good as many 500s,” reaching 56mph in a quarter-mile. Brakes were “well up to standard,” and fuel economy reported as 99.6mpg (Imperial). The testers also noted that the engine “remained remarkably free from oil leakage” throughout the test. Their only complaint: a definite flat spot in the power curve under acceleration, “which caused the engine to cough momentarily.”

But by 1938, the company was in financial trouble, and was sold to Bruce Douglas, nephew of the founder of Douglas Motorcycles. The Matchless-powered Calthorpe Cavalier was sold for one year, 1939, before hostilities interrupted (www.calthorpe.info).

The DJ Run

Between 1913 and 1936, what must have been one of the most challenging motorcycle races ever was run in South Africa between the coastal city of Durban and the interior hub of Johannesburg. The race ran over 420 miles (roughly the distance from Denver to Albuquerque, New Mexico) on the “unimproved” (dirt) roads of the day. The conditions were atrocious: deeply rutted wagon tracks, open “veldt” (prairie) with grasses up to 7 feet high hiding treacherous sinkholes and levees. Riders negotiated farm gates (which they were required to open and reclose), and at least one rider was almost decapitated by a wire strung across the top of a gate. Broken bones and fractured forks were common, but the first rider home in 1913 was A.W. McCaig of Johannesburg on a 544cc Bradbury, completing the course in 14 hours, 46 minutes at an average speed of 29mph.

Image by Robert Smith

The 348cc air-cooled single is fed by a non-stock Amal 276 carburetor.

The race was run every year from 1913 to 1936 (except for the war years). However, the death of a popular 25-year-old racer, Jock Leishman, in the 1936 event, decided the organizers that the race had “outlived its usefulness.”

But the spirit of the DJ lived on, and in 1970 the name was revived for a regularity trial for motorcycles made before 1936, meaning speed was less important than arriving at each checkpoint at the right time. Winner of the 1970 DJ Run was G.L. Palmer riding a 1926 Royal Enfield, with an aggregate timing error of 5 minutes, 34 seconds. The DJ has run every year since, now over two days, and with an entry list in 2019 of 79 riders (www.djrun.co.za).

Clive Curry and the DJ

Clive Curry is a recent emigrant from South Africa now living in British Columbia, Canada. Among the effects that moved with him to his new home was a 1930 Ivory Calthorpe 350.

Curry had always wanted to ride in the DJ but lacked one essential item — a suitable pre-1936 motorcycle. So he went looking for one. But the 350 wasn’t his first DJ bike. Nor was it his first Calthorpe.

“I was looking for a bike and I heard in my club that there was a mechanic who had a vintage bike he might want to sell. It was a 500 Calthorpe. But he just had the frame and a few bits and pieces. It was about one-third of a bike.” Regardless, Curry bought the collection of parts. But he still needed a running DJ bike. “I went to the start of the DJ one year. Picture about 130 vintage bikes in an underground parking lot!”

One of the competitors was riding a 1935 Velocette MSS. He didn’t get very far. “He just got out of the parking lot, and then the bike stalled. He couldn’t get it restarted,” Curry says. Regardless, it seemed like the perfect bike for the run, and Curry got to know the owner through the Veteran and Vintage club.

“Eventually I saw that the Velocette was for sale. So I made an offer.” After collecting the Velocette and getting it home, Curry started checking the bike over. “I looked in the oil tank and it didn’t look like nice clean oil,” he says. So Curry poured the oil out and poked around inside, finding that the tank also contained a hornet’s nest! After draining and cleaning the oil system, Curry tried to start the Velo without success. A new carburetor and a rebuilt magneto did the trick. So Curry entered in his first DJ around 2007.

“In my first run, we got to just past Ladysmith (about 150 miles from the start) and my front wheel bearing packed up.” That was the end of Curry’s first DJ. But he returned the next year, again with the MSS, and this time finished the run — in spite of a broken frame tube! “So I had a terrible ride with a headshake all the way through to Joburg.”

Image by Robert Smith

The large wooden box on the handlebars is a route sheet holder.

It was while he was searching for parts for the 500 Calthorpe that Curry found out about a complete Calthorpe for sale in Johannesburg.

“I met [DJ luminary] Mike Milner-Smyth, who said he knew a person who had a Calthorpe up in Joburg. It was the Calthorpe I actually ended up buying.”

It turned out the 350 Calthorpe had quite an interesting history. It had been rebuilt specifically with the DJ Run in mind. But the owner died after only a small number of entries. However, his widow took over the Calthorpe.

“She remarried and did quite a few DJ runs on it,” Curry says.

At that time, she decided not to part with the Calthorpe. But not long after, Curry saw the same bike for sale on South Africa’s Junk Mail online marketplace. A price was agreed, and Curry collected his new machine. And though it was running, it needed a lot of work. In particular, the valves guides were badly worn, so a cylinder head rebuild was in order.

Curry first entered the DJ Run on the Calthorpe in 2009, with follow-up rides in 2011, 2012 and 2013. He finished all four runs, though of course not without incident. That said, the most serious problem with the Calthorpe was difficult starting on one run that required a push start each time he stopped. Curry estimates that through its three owners, the Calthorpe has completed at least 20 DJs!

The DJ Run also allows competitors to choose whether to run in faster or slower groups.

“I got my best position on the Calthorpe when I finished in the slowest group. I think if you go in a lower speed group you’ve got a better chance because you can correct your time much easier. But it’s bum-numbing!”

Another problem Curry discovered running in the slower groups was clutch wear from slipping the clutch. The clutch plates would score the basket, which needed repairing after each Run.

“And the bike wants to go faster, so it’s much more fun if you do it without worrying too much about your position and just having a fun ride.”

Overall, though, Curry is very enthusiastic about the DJ Run.

“The organization that goes into it is really fantastic. There’s a camaraderie there that you can’t believe. Everybody sort of pitches in and helps out. And unfortunately, it’s getting to the days now where those sort of people are dying out. And I don’t know how much longer it will carry on. But luckily there are some young people that are coming in.

“But you need the people that are retired and have the time and the money to be able to organize things like that.” MC

Published on Feb 13, 2020

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