Quality and Reliability

Working to very close engineering tolerances on the production of the Rotax engines would be rewarded with an excellent reputation for reliability. Many critics of the change to a disc-valve engine pointed out that the system would require an ongoing development period to benefit from its attributes. The 250cc Rotax motor that SWM started with was from the Enduro machine with a 72mm cylinder, but to increase performance it was opened up to 76mm which increased the size to 276.6cc. Torque from the engine was a problem and to improve this the flywheel had a an extra weight fitted to it. Early test results in action were very encouraging, as the riders praised the power delivery and also the fact that it would rev out so high.

The other major benefit was the smooth power delivery. The engine provided four very close trials gear ratios using the straight-cut gear technology, with the other two available for open trail and road use.

The Dell Orto carburettors are well known for their quality performance and delivery of the air–fuel mixture, and after many tests the 24mm was standardised for trials.

The decision was also made to continue with a points ignition system which optimised a strong spark at very low engine revolutions. As the engine was developed in the trials world the power surge was the main problem, but a new design of the exhaust system soon eradicated this. After complaints about the cable operated clutch mechanism the internals were improved, which complemented the excellent gear selection.

After the first year of production a three-bearing crank was introduced to make a smooth engine even better. Apart from small changes to the engine which would be used in the SWM, Aprillia, Moto Gori and later the CCM/Armstrong, development would be very little. Each manufacturer would make their own changes in an effort to have the edge over the others.

Jumbo

With constant requests from the top riders for more power SWM looked around at what other engines Rotax were using. In 1982 they started to develop for trials the 350cc engine, which was originally aimed at the Motocross and Enduro market. Rotax had always been associated with the rotary disc valve, but this engine was very conventional and moved back to a normal induction system through a reed-valve block mounted directly onto the cylinder barrel. A novel idea was the addition of another lever for the clutch cable under the fuel tank to make the clutch action lighter. The spinning rotary disc valve was tried but soon abandoned. Vibration was also a problem with such a large, single cylinder twostroke. SWM persevered with this engine but really it wanted much more development. Armstrong produced a small batch of machines using this 350cc engine but in truth it was not ideal for the world of trials.

As SWM fell into financial ruin, with no money available to develop new ideas it was rival Italian brand Aprilia who took the lead and developed the engine further. Its TX 300 model was developed and fine-tuned as they were preparing to move into the mono-shock area, and further down the line they would ultimately deliver the trials world the very first production water-cooled machine in the late eighties.

Italian rider Danielo Galeazzi was always spectacular to watch in the WTC and a regular points scorer. He won the National Championship from 1980 to 1983 on an SWM.

After starting with Bultaco, John Lampkin moved to SWM with support from his uncle Martin Lampkin at the start of his adult trials career.

The Italian Moto-Gori machines, using Rotax power, made an impact on the UK trials scene with a team of riders including Mike Leddy, seen here at the 1980 Northern Experts. Other riders included Brian Higgins, Ian Wetherill, John ‘Wack’ Walker, Tony Calvert and John Hulme, to name a few.

Cheshire-based David Hooke was a mainstay of the Moto-Gori trials efforts in the UK.

Nigel Pearson from the Trials UK shop based near Leeds owned one of the early 200cc Moto Gori’s which were very popular as an easy to ride clubmen machine. We note that he is wearing no crash helmet but this image certainly captures the spirit of a true trials enthusiast.

In mid-1984 Steve Saunders rode this Rotax 350cc Armstrong in the American World round, but did not like the harsh power it delivered.

1985 SSDT: ‘Crazy Bert’ Phillipe Berlatier was always a very popular visitor to the ‘Scottish’. The Aprilia features rear air-shock absorbers before the move to the mono-shock model in 1986.

1985: French rider Phillipe Berlatier movedfrom Italjet to Aprilia knowingthat a new mono-shock machine was on the horizon.

1985: Armstrong produced a small batch of machines using the 350cc Rotax engine.

1984 SSDT: Howard Jackman is seen here with the 240cc Rotax Armstrong.