CCM Four-Stroke


The cot­tage in­dus­try of mo­tor­cy­cle man­u­fac­tur­ers that is so prom­i­nent in Great Bri­tain has an abun­dance of tal­ented engi­neers, who all have their own dreams and ideas of what they be­lieve will work in the hugely com­pet­i­tive world of off-road mo­tor­cy­cling. We wit­nessed this in tri­als with John Shirt Snr and the Majesty

Yamaha pro­ject, and Graham and Nick Beamish (Beamish Suzuki) with their own ideas for a pro­duc­tion tri­als mo­tor­cy­cle. Af­ter Sammy Miller blew the di­nosaur four-stroke sin­gle cylin­der tri­als ma­chines of old into ex­tinc­tion with his two-stroke Bul­taco in 1965 it ap­peared that four-stroke tri­als mo­tor­cy­cles were dead and

buried for­ever. In 1978, how­ever, a cer­tain Alan Clews had other ideas tick­ing away in his head.

Alan Clews was very fond of the four-stroke en­gines, us­ing pro­duc­tion stock in­clud­ing en­gines and com­po­nents he pur­chased when the mighty BSA Em­pire col­lapsed. He had tasted suc­cess in the world of Mo­tocross, or Scram­bling as it was called then, with his own ma­chin­ery pow­ered by the four-stroke mo­tors. Quite by ac­ci­dent he had taken a Bri­tish tri­als ti­tle in 1973 with Jack Matthews in the Side­car class on one of his early ‘Clew­stroka’ ma­chines.


Back in ‘The Day’ both Tri­als, a win­ter sport and Mo­tocross, a sum­mer sport, were very sea­sonal, which also af­fected sales of ma­chines. CCM ma­chines had tasted suc­cess and were a very well re­spected brand name in the Mo­tocross world. The ma­chines, us­ing four-stroke mo­tors, were pro­duced by a ded­i­cated work force but as with any sea­sonal prod­uct what do you do with that work­force dur­ing the close sea­son? An avid off-road fan, Clews had had sat back and watched the Honda tri­als pro­ject take shape in the ca­pa­ble hands of Sammy Miller in the early sev­en­ties which had pro­duced the TL 125cc and 250cc. The tri­als world was set alight when Rob Shep­herd won the 1977 Bri­tish ti­tle un­der Miller’s guid­ance. When the bomb­shell, that Honda would not be con­tin­u­ing with Sammy Miller, was dropped it looked like the four-stoke re­turn would once again be a dream. As it hap­pened Honda did con­tinue with Shep­herd, who would go on to take the first ever WTC win in the FIM world cham­pi­onship se­ries, but dis­posed of the ser­vices of Miller. Still very pas­sion­ate about the fourstroke tri­als en­gine, Miller ap­proached Clews with a view to pro­duc­ing a new mo­tor de­signed just for tri­als. Af­ter look­ing at de­vel­op­ment and tool­ing costs of a new mo­tor Clews de­clined the op­por­tu­nity to pe­ruse the ven­ture with Miller.

As the win­ter months of 1977 rolled into 1978 Clews was given the op­por­tu­nity to look at one of the Honda tri­als ma­chines and he went away with many thoughts run­ning through his head. He spoke about a CCM tri­als pro­ject with his good friend Jim San­di­ford, who was the suc­cess­ful UK im­porter of the Span­ish brand. He pur­chased a full front end of a Mon­tesa Cota from San­di­ford and the CCM four-stroke tri­als pro­ject was born. The idea of a tri­als pro­ject would also an­swer the ques­tion of what to do with the ded­i­cated work force dur­ing the re­main­der of the win­ter months.


Clews knew that the mar­ket­ing of a new fourstroke tri­als ‘Iron’ would be the easy part as he had the mo­tocross net­work of deal­er­ships al­ready in place, but the man­u­fac­ture of a ma­chine would not be so easy. With the end of the Miller Honda tri­als team in 1977 Clews went straight to ex-team mem­ber Nick Jef­feries and of­ferd him a con­tract to help with the de­vel­op­ment pro­gramme of the pro­posed new ma­chine. Jef­feries had learnt so much from the Honda pro­ject that Clews knew he would be a valu­able as­set to the de­vel­op­ment of the new ma­chine.

Both Clews and Jef­feries tested many of the new mod­els on the tri­als mar­ket be­fore they sat down and dis­cussed which di­rec­tion they would go in but they both agreed on the most im­por­tant fac­tor, that it would have a four-stroke mo­tor.

Af­ter dis­cussing many op­tions they went for a hy­brid BSA B44/B50 en­gine us­ing a bore and stroke of 79mm x 70mm, which pro­duced an en­gine ca­pac­ity of 343cc, the same as the old BSA B40. The spe­cialised Al­pha En­gi­neer­ing Com­pany would pro­duce the ‘Big End’ of the mo­tor us­ing a B40 con­nect­ing rod pressed in with a steel crankpin with a caged roller bear­ing for a smooth op­er­a­tion. The BSA B44 cast­ing would be used for the cylin­der head and bar­rel. The en­gine lu­bri­ca­tion would be taken care of with the oil car­ried in the tubu­lar steel frame. Smooth op­er­a­tion is es­sen­tial in a tri­als mo­tor and the pro­to­type fly­wheel weights would start at 5½lbs on ei­ther side of the crank. Mag­ne­sium Ital­ian Marzocchi forks would take care

of the front sus­pen­sion and at the rear they con­tacted Gir­ling, who they had worked closely with in Mo­tocross.

Af­ter the burn­ing of much mid­night oil the first four-stroke pro­to­type tri­als ma­chine was pre­sented for test­ing to Nick Jef­feries on Satur­day 4th Fe­bru­ary 1978. In se­cret over the week­end Jef­feries went to his lo­cal prac­tice area and gave the ma­chine a long work­out. As ex­pected with any pro­to­type ma­chine un­seen prob­lems soon came to the sur­face.

The mo­tor was over-heat­ing and the low-speed power was like an elec­tric light switch, ei­ther on or off. To help erad­i­cate this prob­lem the fly­wheel weight was in­creased to 7.8lbs on each side and to help the mo­tor run cooler the oil ca­pac­ity was in­creased. The rear shock ab­sorber po­si­tions were also changed. Af­ter more test­ing the han­dling was im­proved as the steer­ing head an­gle was pulled in by two de­grees and the swing­ing arm ful­crum point was lifted to im­prove ground clear­ance. When Jef­feries had ap­plied the power at the first test it pulled the sus­pen­sion down, which in turn re­duced the all-im­por­tant ground clear­ance. Even though the ex­haust sys­tem worked well it was changed to re­duce the out­put noise. To help with start­ing, and the power out­put of the mo­tor in gen­eral, a 24mm Amal car­bu­ret­tor was fit­ted and Clews ap­plied his four-stroke knowl­edge to fine tune its per­for­mance in cer­tain ar­eas.

CCM – Clews Com­pe­ti­tion Ma­chines. TRIAL MAG­A­ZINE

Which­ever way you look at the hy­brid four-stroke BSA B44/B50 air-cooled sin­gle cylin­der mo­tor, it’s ‘Big’.

It’s 100% con­cen­tra­tion for Nick Jef­feries as he stays ‘Feet Up’ on the sec­ond pro­to­type at the SSDT.

The fuel tank and seat were easily re­mov­able for main­te­nance. 70

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