1931 Ivory Calthorpe 350cc Sports

• Purchased as a 'basket case'
• Restored by the vendor
• Modelled on a Calthorpe raced in Austria

Manufactured by the Minstrel & Rea Cycle Company, of Birmingham, the first Calthorpe motorcycle appeared in 1909. The following year there were no fewer than six Calthorpe models displayed at the Motor Cycle Show at Olympia. In 1928 the first of the famous 'Ivory' Calthorpes appeared, so called because of its distinctive finish to fuel tank and mudguards. By 1930 the Ivory had gained a new 350cc overhead-valve inclined engine with twin-port cylinder head. Two new Ivories were added for 1932: a 250cc two-stroke with Villiers-based engine - the Ivory Minor - and a 494cc version of the OHV model. The Minor lasted for little more than a season before the Calthorpe range was reduced to just the 494cc Ivory Major. The Minor was revived in 1934, but this time with a 250cc four-stroke engine, while the '350' returned for 1935 as the Ivory Junior. South London dealers Pride & Clarke held exclusive sales rights to the range for 1937 but Calthorpe would not survive for much longer, going into receivership in 1938. The brand was revived briefly post-war by DMW, though production machines used the latter's name only.

Built as a replica of an Ivory Calthorpe raced in Austria, this '350' is one of only 11 in the world registered with the VMCC. The machine was purchased in a totally dismantled state: wheels missing and gearbox dismantled but all parts wrapped in oily rags. The vendor dismantled the engine, finding that the high-compression had a hairline crack so would need to be replaced. The cylinder was rebored +0.030" and a suitable new high-compression piston fitted.

The crankcases were checked and the oil pump found to have a problem: the outer casing is made of Mazac, which was the downfall of many Calthorpe engines. The oil pump's Mazac end-cover would corrode, even in oil, and end up like a 'digestive biscuit' causing loss of oil pressure. Fortunately, on this engine it had not totally failed and a new end-plate was made in bronze; the pump was then checked and reassembled. A pair of pushrod tubes was purchased from Australia. The flywheels were built up and bearings replaced before the engine was finally reassembled. An oil pressure gauge has been fitted, typically showing 5-10psi when started and around 2psi when running. The BHT magneto was rebuilt and tested.

The gearbox had been dismantled but everything had been kept in oily rags and was in good condition. The vendor reassembled the gearbox, overhauled the clutch assembly and fitted new clutch plates. The Calthorpe steering damper control was specially made by a local engineering company: it was machined in aluminium to match the original broken Bakelite one reproducing all the original details. The details were laser etched into a block of carbon then spark eroded to recreate the originals. The vendor made new handlebars and had them chrome plated to match the original.

The vendor also made a new fuel tank using the original as a pattern, including the new hand change mechanism. The fuel tank and mudguards were sprayed in Ivory colour and Calthorpe transfers applied. A new rear wheel was built and a tyre fitted. The vendor managed to obtain a front wheel and brake hub. New brake shoes were fitted. The frame was sand blasted and painted, and the Druid girder forks refurbished, their worn bushes and link arms being replaced. A new seat was fitted. Straight-through exhausts were made and fitted, and copper inserts incorporated to reduce the noise level. Stainless steel clutch and brake end-levers were fitted. The original Helix twist-grip was refurbished and new original twist-grips and control cables fitted. A new Smiths speedometer was fitted. Restoration was finished in April 2013, and the Vendor took the Calthorpe to Isle of Man and rode it around the circuit several times: not to race, just for the experience!
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