Frame #1 – 1975 Sparton 500

In England, Race by Tim Huber0 Comments

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In the latter-half of the 1970’s, manufacturers were pouring massive amounts of funds into the R&D of race machines. Yet for a time, the most powerful racer was a machine built in a chapel’s workshop in Caernarvonshire in the UK. Sparton Motorcycles was a collaborative effort between Spondon Engineering and Barton Motors. From 1974 to 1982, the engineering companies joined forces to combine their respective expertise as Spondon specialized in frames and Barton was a seasoned tuner and builder of two-stroke racing engines.

In ’75 Sparton built its own 500cc square-four engine based on a revised Suzuki RG500 motor. This powerplant would be the basis for Sparton’s future 500cc and 750cc engines that the boutique manufacturer would produce in minuscule numbers. Barton Motors got its start producing racing gearboxes for Japanese bikes before moving on to clutches and then cylinder barrels and heads. Rex White of Suzuki Great Britain would eventually approach Barton Motors, asking the small operation to apply its expertise to a 350cc Suzuki that Barry Sheene would be piloting. Barton took a Suzuki GT380 and turned it into a water-cooled machine that retained the GT380 crankcases and crank. Early testing revealed the machine to be seriously fast.

The 350 looked promising as hell, however Sheene was under contract with Suzuki who caught wind of the project and promptly shut that shit down. Without the additional development that the 350 still needed, the project would end up dead in the water – never having been officially raced – though Barton had still done some superb work that the motorcycle world began to take notice of. In ’74, the 350cc three-cylinder Sparton was becoming increasingly refined. Its engine featured a 52 x 54mm bore and stroke and used the bottom end from a Suzuki with special gear ratios. Sparton was pleased with the power the engine was making, but it was still noticeably heavier than Yamaha’s twin, so the following year Barton would utilize magnesium cylinder blocks and chromed aluminum liners. After a number of delays in the machine’s development – primarily waiting on the special piston rings the 350 necessitated – Sparton would opt to sell the 350 to Monster Car Hire at Thames Ditton for Peter Dalby to pilot, and then focus on taking what was learned from the 350 and applying it to a 500.

The first versions of the Sparton 500 engines actually featured a 458cc displacement using Omega pistons with a bore and stroke of 60 x 54mm, and still utilizing the crankcases from Suzuki’s GT380. Because the GT380 used cylinders that were widely spaced apart to enable optimal airflow around the barrels, the water-cooled Sparton was able to fit water jackets. A gear-driven water pump on the drive side of the Barton was another difference between it and the Suzuki, as well as a Krober electronic ignition which was driven directly from the other side of the crankshaft. Inside the crankcases a few other differences could be found. An extra bearing was added on the Sparton as a result of the small supporting area on the timing side of the crankshaft. An additional 525cc Sparton variant was created that used Yamaha pistons and made 100 hp.

The 458cc Sparton was now putting down an impressive 95hp, especially when compared to the GT380’s 37hp. Though Sparton had continued to establish its name and reputation among the racing and tuning communities, it was at the 1975 Isle of Man TT that the 500 would solidify its place in history. Martin Sharpe was clocked at 146mph at the speed trap. This was on par with the Works Kawasaki which was developed with substantially more funding and a much larger team. The following year, the Sparton would be ridden to victory at the famous North West 200, with riders Martin Sharpe and “Big” Frank Kennedy – who both competed aboard Spartons – claiming the top two steps of the podium that year. A revised 497cc short-stroke version of the Sparton reportedly put down somewhere between 105-110 hp and was capable of a 160mph top-speed. In ’77 Graham Wood – while competing as a privateer – would bag a dozen firsts aboard the Sparton 500.

According to one source, the Sparton engine cost £1,300 ($1,700) on exchange ($1,900 or £1,450 complete) compared to Suzuki’s RG500 which supposedly sold for more than double that. The more accessible price did come at a cost however as the Sparton suffered from some reliability issues as a result of using 380cc Suzuki crankcases. A major goal for Sparton was to produce machines that could rival the better-funded Japanese scoots of the era, so the introduction of a 500cc and 750cc square four was a natural step for the small manufacturer to take. The 750cc square four (called the “Phoenix”) used disc valves instead of reed valves which could reduce top-end power. The Phoenix operated similarly to the RG, though an array of internal improvements were made in an effort to strengthen the engine and bolster its reliability. Reinforced crankcases, internal crankshaft coupling was improved, the gearbox was strong and the clutch – which used Yamaha 750 clutch plates – was lighter than the RG’s. The bearing support and lubrication on the Phoenix was another improved aspect over the RG500.

By the beginning of the 1980’s, Sparton had only produced ten Phoenix units, (eight of which were 750’s and two 500’s). Sparton still needed real-world feedback on its machines in hopes of further developing them. The company stated it “wish(ed) to sell these engines to people who are prepared to work with us to solve any problems that may occur,” though the plan wouldn’t really come to fruition. Racers would continue to pilot Sparton machines to various victories including Graham Wood who would beat Ron Haslam aboard his OW31 Yamaha in 1978 at Donington.

This particular 1975 500cc two-stroke Sparton triple features Suzuki 380cc crankcases used with Suzuki flywheels. However, they’ve been machined to accept Barton crankpins, (Yamaha) TZ connecting rods with Omega pistons, and Barton water-cooled cylinders. The water pump and primary cover on this example were manufactured by Barton Motors, and the clutch is a Suzuki multi-plate dry type. Its ignition is Krober and its gearbox has been modified by Barton as well with some modifications to the ratios. According to the seller, the power on this machine comes to life around the 8,000 rpm-mark and is said to boast a rather unique exhaust note. Expansion chambers of the bike are original and this example is said to have excellent handling, as multiple sources online confirm. The original Spondon brake calipers have been “expertly restored” on this example too.

Very few of these machine were ever built, and they undeniably have a unique place in history, despite the company being one of the lesser known manufacturers. The original bodywork is one of my favorite features on this example, and though it would make a great living room piece, this example is a competent vintage racer that would be a blast to track. The fact this machine accepts an array of existing parts from larger manufacturers also makes sourcing replacement parts for this example a lot easier. You can check out a video of a Sparton 500 being fired up, it really does have a cool sound too:

You can find this 1975 Spartan 500cc two-stroke three-cylinder racer with frame number 001 for sale here on RaceBikeMart.com in the UK with a price of $52,750 (or £40,000).

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