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
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.