Classic Trial - - CONTENTS -

It’s quite in­ter­est­ing to note that the con­nec­tion of the old and new in the ideas stakes al­ways fol­lows a fa­mil­iar trend in life. The tri­als en­gine is, in many cases, de­vel­oped for this unique off-road dis­ci­pline and in my opin­ion is a su­perb me­chan­i­cal

en­gi­neer­ing ex­er­cise. In the days of the Bri­tish dom­i­nance in tri­als the two- and four-stroke en­gines from the var­i­ous man­u­fac­tur­ers’ road-based ma­chines were univer­sally used in com­pe­ti­tion ma­chin­ery, with mod­i­fi­ca­tions. In more mod­ern times

we can wit­ness the same tri­als power plant de­vel­oped for the sport and used in the Scorpa and Sherco. Here we look at the Sammy Miller in­spired Hiro mo­tor which fol­lowed a sim­i­lar fash­ion, as it went on to power Euro­pean based tri­als ma­chines from

the cot­tage in­dus­try of Arm­strong/CCM and Trans-Am through to the prom­i­nent in­dus­try names of Aprilia and Garelli. Words: Steven Crane • Pic­tures: Sammy Miller Mu­seum, Eric Kitchen, Alan Vines, Toon van de Vliet,

Mauri/Fontsere Col­lec­tion and the Gi­ulio Mauri Copy­right, Solo Moto and Jean Claude Com­meat

Af­ter ap­ply­ing his en­gi­neer­ing skills to the mighty four-stroke Ariel 500 — Reg­is­tra­tion no. GOV 132 — Sammy Miller started overnight the trend of the tri­als mo­tor­cy­cle de­vel­op­ment with the two-stroke Span­ish Bul­taco in 1965. From then on­wards the world of tri­als would be changed for­ever, con­tin­u­ally in­flu­enced by that man Miller. He moved back to four-stroke mo­tors in the early seven­ties with Honda be­fore a brief spell was spent with the reed-valve in­duc­tion Ro­tax two-stroke en­gines with SWM. In re­al­ity though the dream had al­ways been to design and pro­duce a tri­als mo­tor­cy­cle, which now leads us into the Hiro en­gine story.


It was dur­ing the seven­ties that Sammy Miller and Alan Clews — the Arm­strong/CCM founder — had first come into con­tact when they spoke to dis­cuss the pos­si­bil­ity of Clews sup­ply­ing Miller with a sin­gle cylin­der four-stroke tri­als en­gine ded­i­cated to the needs of the tri­als mo­tor­cy­cle. Af­ter do­ing the maths it was soon pretty ob­vi­ous that the tool­ing and man­u­fac­tur­ing process for the project would not make it cost ef­fec­tive. It was dur­ing his time with the SWM project that Miller had started to look at the pos­si­bil­ity of find­ing a man­u­fac­turer who he could be­come in­volved with to pro­duce a tri­als en­gine.

In early 1978 ne made con­tact with Ital­ian An­drea Mis­coni, who owned the Hiro name which pro­duced mo­tor­cy­cle en­gines for man­u­fac­tur­ers such as An­cil­lotti and Garelli. They both had their own ideas and when Miller put his ques­tions con­cern­ing de­vel­op­ment and pro­duc­tion Mis­coni could an­swer all of them, and so an agree­ment was ar­rived at.

The new mo­tor would be a sin­gle cylin­der air-cooled type with an en­gine ca­pac­ity of 305.8cc, a bore of 78mm and a stroke of 64mm which was quite long for the tri­als ap­pli­ca­tion but would de­liver smooth us­able power. The five-port alu­minium cylin­der bar­rel would be at­tached to the crankcases, which would be based around a 250cc mo­tocross mo­tor us­ing a six-speed gear­box with ex­tra fly wheels on both sides of the crank­shaft. The car­bu­ret­tor would be in­creased from a 25mm Ø to a 26mm Ø Dell’Orto to im­prove the power de­liv­ery. To help keep the costs down it would use a nor­mal con­tact breaker ig­ni­tion sys­tem.

The Miller 350

The new mo­tor would be housed in one of Miller’s own tubu­lar steel ‘Hi-Boy’ frames. Miller had suc­cess­fully sold over 400 of the ‘HiBoy’ frame kits in­clud­ing around forty-five com­plete ma­chines us­ing the Vil­liers mo­tors in the late six­ties. It also ap­peared in a dif­fer­ent con­fig­u­ra­tion hous­ing the four-stroke Honda tri­als project dur­ing his work­ing time with the Ja­panese man­u­fac­turer.

The new tri­als project would use the mul­ti­tude of com­po­nents avail­able from sup­pli­ers such as Mar­zoc­chi for the front sus­pen­sion, Grimeca for wheels and hubs and Be­tor oil-filled shock ab­sorbers for the rear sus­pen­sion, with the other com­po­nents com­ing from Miller’s suc­cess­ful range of af­ter­mar­ket tri­als parts he sup­plied around the globe. Miller would build three com­plete ma­chines, to be named the Miller 350 model.

Sammy did the ma­jor­ity of the de­vel­op­ment work him­self in the early stages of the project but also en­rolled the ser­vices of Ge­off Parken and John Met­calfe to as­sist him.

When he de­cided the time was right he looked at the idea of launch­ing the ma­chine into pro­duc­tion with an ini­tial pro­duc­tion run of 100 ma­chines. The Hiro mo­tor cost for pro­duc­tion was around the £350 mark and when all the other costs were taken into ac­count it was soon ob­vi­ous that it could not be turned into a fi­nan­cially vi­able op­tion and the idea was shelved, much to Miller’s dis­ap­point­ment. One of the three ex­am­ples can still be found in the su­perb Sammy Miller mu­seum col­lec­tion.


This brand name was cre­ated by the Swiss-Ital­ian Luigi Mal­try, with the col­lab­o­ra­tion of in­dus­tri­al­ist Paolo Cam­pan­elli who was the boss of the fac­tory bet­ter known for its mo­tocross and en­duro ma­chines dur­ing the seven­ties and eight­ies. The Transama 320 is one of those rare ma­chines that didn’t have much suc­cess in com­pe­ti­tion or on the sales chart but is in­stead bet­ter known for its rad­i­cal en­gi­neer­ing. A full story can be found in is­sue 4 of Clas­sic Trial Mag­a­zine.

The Hiro mo­tor was cho­sen for the project and was the same as that fit­ted to the Aprilia. The chas­sis was what sep­a­rated this ma­chine from all the oth­ers on sale. Mal­try adopted a sin­gle curved spine frame and hung the mo­tor from it. The fuel tank was lo­cated un­der the seat and used the main frame tube as a pas­sage for the air fil­ter, which was mounted on the steer­ing column be­hind the num­ber board. The swing­ing arm was unique in the fact that it had two mount­ing points which al­lowed a change in wheel­base. The chain ad­just­ment was car­ried by two ec­cen­tric cams fit­ted to the swing­ing arm pivot.

In ac­tion the ma­chine was very im­pres­sive and was im­me­di­ately put into pro­duc­tion, and the ma­chines were in deal­ers in early 1980. The ma­chine was very un­usual in ap­pear­ance and you ei­ther loved or hated it. Com­mer­cially it was never a real suc­cess and the last ma­chines were sold in 1985.


Not want­ing to waste all the pro­duc­tion costs in­curred with the de­vel­op­ment of the Hiro tri­als mo­tor Mis­coni spoke with fel­low Ital­ian com­pany and mo­tor­cy­cle man­u­fac­turer April­lia about the pro­duc­tion of a tri­als ma­chine. The Hiro mo­tor, which had been fur­ther de­vel­oped, would be fit­ted in the new April­lia TR 320 with the cylin­der ca­pac­ity in­creased to 321.6cc by in­creas­ing the bore to 80mm. Koku­san elec­tronic type ig­ni­tion was fit­ted and the Dell’Orto car­bu­ret­tor size in­creased to 28mm Ø.

The model was re­leased in 1981 us­ing sim­i­lar com­po­nents to the Miller in­clud­ing Mar­zoc­chi front fork, Be­tor rear shocks and Grimeca brakes. The later model, the ‘Trial 320’ ar­rived in 1982 and re­ceived only a few mi­nor mod­i­fi­ca­tions and a change in colour from red to white. They would change from the Hiro mo­tor to the Ro­tax in 1984.


Alan Clews had watched the Miller project with in­ter­est and de­cided that the time was right to launch his own vari­ant of a Hiro pow­ered tri­als mo­tor­cy­cle. You can read the full story of Arm­strong/CCM in tri­als in is­sue 11 of Clas­sic Trial Mag­a­zine but here is a brief over­view of the project.

CCM boss Alan Clews was the orig­i­nal im­porter of the Hiro en­gines with his mo­tocross ma­chines and, us­ing the Miller 350 as a bench­mark, he pro­duced a prototype car­ry­ing the Arm­strong badge. Two pro­to­types with dif­fer­ent char­ac­ter­is­tics were hand-built and tested by var­i­ous rid­ers be­fore Clews and Jef­feries de­cided on the fi­nal ma­chine to be used for pro­duc­tion.

Af­ter some ini­tial test­ing with Nick Jef­feries which proved suc­cess­ful he or­dered 120 of the orig­i­nal 305.8cc mo­tors, and the first pro­duc­tion run of the model named the CCM CMT 310 was started in June 1981.

The tubu­lar steel frame fea­tured an alu­minium sump guard as a stressed frame mem­ber but was very con­ven­tional in ap­pear­ance, and the first mod­els were re­leased to the Arm­strong/CCM net­work of mo­tocross deal­ers priced at £1,395. Based on the suc­cess of Jef­feries, John Lampkin tested the ma­chine and was happy to sign a fac­tory con­tract with Clews for the 1982 WTC sea­son.

In the tough com­pe­ti­tion of the WTC the few prob­lems en­coun­tered led to a new mod­i­fied model named the Arm­strong CMT 310 MKII. The mod­i­fi­ca­tions in­cluded a wider sump shield to pro­tect the clutch cover, Koku­san elec­tronic ig­ni­tion, lighter wheel rims and a new chain guide.

With Steve Saun­ders re­plac­ing John Lampkin in 1983 a new ma­chine was also un­veiled at the Scot­tish Six Days Trial named the Arm­strong CMT 320, fol­lowed by a 250 model in the June. The new ma­chine fea­tured a num­ber of sig­nif­i­cant changes and a move to a white-coloured frame and a price tag of £1,449. With no fur­ther de­vel­op­ment of the Hiro mo­tor Arm­strong moved to Ro­tax power in 1984 for its tri­als ma­chines.


This Ital­ian brand’s main forte in the eight­ies was the pro­duc­tion of a range of mopeds and small mo­tor­cy­cles, but in 1984 they made the bold de­ci­sion to en­ter the tri­als world with a Hiro pow­ered ma­chine. De­spite the ar­rival of the sin­gleshock ma­chines that would change the tri­als world for­ever, they went with a twin-shock ma­chine. De­vel­op­ment would be car­ried out dur­ing 1984 with ex-world cham­pion Bernie Schreiber from America. The first prototype would ap­pear in March with the Hiro mo­tor housed in an SWM ‘Jumbo’ model frame, which was no sur­prise as Schreiber had rid­den in 1983 for SWM.

The new chief en­gi­neer for the Garelli project was also an ex-SWM em­ployee, Ital­ian Dario Seregni. It was an easy op­tion to use the Hiro mo­tor used in the old Arm­strong and Aprilia tri­als ma­chines but it was now lack­ing in per­for­mance com­pared to what the other man­u­fac­tur­ers were us­ing. At the end of the year the new pro­duc­tion ma­chine was re­leased at the Mi­lan show. It had fol­lowed a sim­i­lar trend to both the Aprilia and Arm­strong tri­als ma­chines but had in­her­ited an alu­minium swing­ing arm. It would be named the Trial 320 model and looked splen­did with its red frame and blue aes­thet­ics, with a claimed weight of 93kg.

1985 started disas­trously, when Schreiber de­parted frus­trated with the lack of en­thu­si­asm as the Garelli fac­tory could not pro­vide him with a com­pet­i­tive ma­chine. The knock-on ef­fect was the loss of con­fi­dence with the buy­ing pub­lic. The ma­chine promised huge po­ten­tial but the fact was that twin-shock ma­chines had gone out of fash­ion. In all fair­ness the brand did try to res­cue the sit­u­a­tion and pre­sented a new sin­gle-shock model, the Trial 323 priced at a very com­pet­i­tive £1,595. Its main fea­ture was the re­pro­duc­tion of the piv­ot­ing link­age of the rear sus­pen­sion which was very sim­i­lar to the ground break­ing mono-shock Yamaha sys­tem.

Off the back of some good WTC re­sults from its new rider, Ital­ian Donato Miglio, 1986 was a pretty good year for Garelli and the ma­chines be­gan to sell.

A new colour scheme was in­tro­duced for 1987 with the frame now white in­stead of red and dif­fer­ent fuel tank de­cals, but it came with a price in­crease to £1,695. At the year’s end the com­petion de­part­ment closed the door on the tri­als ven­ture.


The Hiro mo­tor had proved very pop­u­lar due to its sim­plic­ity and ease of main­te­nance but it had suf­fered from the lack of de­vel­op­ment. The en­gine design when it was first used was quite mod­ern, with in-gear kick-start­ing and a six-speed gear­box, and it later ac­quired a Nikasil coated cylin­der liner and elec­tronic ig­ni­tion.

Alan Clews had played with a 340cc cylin­der size on the Saun­ders Arm­strong ma­chine in or­der to get more power from the mo­tor, and he also had the sec­ond and fourth gear ra­tios changed to suit the ex­tra power. If you own one of the Hiro pow­ered ma­chines to­day look af­ter it well as en­gine com­po­nents are get­ting very thin on the ground!

The fin­ished Miller 350 tri­als mo­tor­cy­cle as it would have looked had it gone into pro­duc­tion.

The Hiro was ac­com­mo­dated very eas­ily

in Miller’s Hi-Boy frame.

Some of the cylin­der­head cool­ing fins were

re­moved to let the ex­haust sit as low as pos­si­ble in the chrome

fin­ished chas­sis.

Pic­tured here on the Aprilia TR 320 is Jack Gal­loway in the 1981 Na­tional Alan Tro­phy Trial. Ar­riv­ing in 1982, the later model the ‘Trial 320’ re­ceived only a few mi­nor mod­i­fi­ca­tions and a change in colour from red to white. The first pro­duc­tion run of the CCM CMT 310 was started in June 1981. Steve Saun­ders was the new sen­sa­tion on the Arm­strong in 1983.

Ital­ian rider Danilo Galeazzi fol­lowed Schreiber to ride for Garelli in 1984.

De­vel­op­ment rider Bernie Schreiber on the

Hiro pow­ered Garelli.

Garelli in­tro­duced a new colour scheme for 1987 but it was too late. At the year’s end the com­pe­ti­tion de­part­ment closed the door on the tri­als ven­ture. De­spite the ar­rival of the sin­gleshock ma­chines Garelli went with a twin-shock ma­chine.

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