THE RISE, FALL AND RISE OF TWO STROKES
DEREK PICKARD explains why the once all-conquering two strokes disappeared from our roads and welcomes their recent re-emergence as real classics.
Just a few short decades ago, the march of the two-strokes seemed unstoppable. They conquered the many competition classes and everyone was talking about how fast such light and simple bikes were on the road. Only Honda resisted the movement but then released the successful 125 and 250 trail bikes causing the stroker fans to declare a near take-over of road bikes was on its way.
Those fans pointed to the bikes being simpler, having only three basic moving parts, were cheaper to make, went like hell and with oil injection lasted a long time. Unlike the vast range of four-stroke layouts, most strokers could be put into just a few classes: small single cylinder, small to medium twins, and triples. Japanese makers dominated from the early 1960s. Anyway, no fourstroke sounds as cute as a two stroke triple – real period music. The future looked assured: what could possibly go wrong? ‚
Just as they were reaching what seemed like an incredible growth rate came a massive change. Most major markets began to implement strict vehicle emission regulations and dirty engines were no longer legal. While makers like Bridgestone, Suzuki, Kawasaki and Honda got out early and stopped development, it was mainly Yamaha which used its considerable technical expertise to keep going for a few more years making extremely fast water cooled mid-size 250/350 twins. Inevitably as the emissions noose became tighter, the new model two-strokes disappeared from magazine launches. An era had gone. Within the following decade they nearly vanished from the roads and used ones proved difficult to sell. Many were junked.
As decades passed and the classic movement gathered pace, once-popular strokers began to be accepted again. And now their high price reflects the renewed demand. Most buyers are younger than traditional classic bike fans and are now looking to two-strokes to add to their growing collection of mainly big Jap fours. These buyers are impressed at the compact and light bikes that are easily kick started, make a totally different exhaust note and accelerate nearly as fast as much bigger four cylinder bikes. Another attraction is the very different power delivery feel where a two-stroke twin has the same firing impulses as a four-stroke four and a two-stroke triple the same as a four-stroke six. All this from such compact simple bikes too.
But all is not easy for classic fans wanting to add a sports stroker to their garage. Demand has pushed prices high and although parts are still available there is one significant area which is causing concern: while decades ago there were a reasonable number of two-stroke crankshaft rebuilders, now nearly all of those have gone. The ability to press apart two and three cylinder crank assemblies and reassemble them with good alignment may be straightforward from a trade point of view, but it has now nearly all slipped into the past. The very few people now doing it, have very long waiting lists. No sports two-stroke story can ignore the aspect of these bikes which riders love or hate – expansion chamber exhausts. These have the ability to boost power output but at a massive increase in noise.
While a stock two-stroke triple sounds impressively different, a piped twin can be nothing less than uncomfortably irritating. However, they are a definite part of two-stroke history which once gave rise to a large shed-based industry where heaps of makers in nearly all countries were making black bolt-on power exhausts. And in those days, many enthusiasts misbelieved that more noise meant more power. Unfortunately, one of the results of the expansion chamber business was that many owners threw away stock exhausts which are now nearly irreplaceable. And not every classic fan wants an overly loud bike.
Which brings us to 2021 – a massive leap from the stroker heydays of the 1970s. Although a growing number of enthusiasts are considering acquiring a sports twin from years ago, they have to join the high-priced supply queue and maybe settle for a restoration job as one of the few practical ways of reliving the type of performance bike fans once enjoyed incredibly cheaply. Bargain RD350s in good condition disappeared a few years ago.
Were they that good?
For the late 1960s and early 1970s two stroke road bikes really did offer a lot: the performance versions were cheap and went like hell. Although the vast majority were mid-size they met a definite market demand. And with oil injection the engines lasted well despite being thrashed by young riders. Leading producers like Suzuki and Yamaha did very nicely out of their impressive ranges which sold big globally.
What really went wrong?
The 1970s saw the emergence of the green movements all over the world with the auto industry getting a lot of the blame. Huge markets like the USA and Germany began to act quickly on vehicle emissions with definite ceilings of what could be legally registered for road use. As twostroke engines burned oil the bikes didn’t stand a chance and quickly became illegal. Although a few markets still allowed them on the roads, the volumes were down and Japanese factories were forced to bring forward their development of more four strokes.
The strangest application
A few decades ago, Yamaha fancied their chances in the big Indian market where the 350 Royal Enfield was a respected size and a good seller.
So the Japanese giant configured a version of their RD350 as a cheap 350cc motorcycle cruiser with a very modest stage of development to run on low grade Indian petrol. It was made at a third party Indian factory, called the Rajdoot and its detuned engine peaked at 27bhp. With a front drum brake in place of the disc it was produced during the 1980s. While the performance was better than the old Enfield the fuel economy was bad, the bike was too expensive and so the model was withdrawn. ‚
Two strokes today
How the mighty have fallen. From the most promising internal combustion plant seemingly ever-expanding in the 1970s, the current list of applications is very few. The biggest is a range of small power plants such as garden equipment and the largest is marine engines. In between there are applications such as competition off-road bikes, karts and ultra light aeroplanes.
Two stroke legends
• Australian enthusiasts love to recall how Sydney hero Joe Eastmure rode a 350 twin Suzuki to an outright provisional win the Castrol 6 Hour Production race in the early 1970s humbling the big fours.
• Trail bikes boomed in the 1970s and most were 250 two-stroke singles that sold big in most markets. And the DT175 Yamaha trail bike was so popular for city use it was Europe’s top seller for many years. • Yamaha’s production two-strokes dominated global racing for nearly two decades with air and watercooled twins and fours.
• Despite the boom, not all two stroke factories ran profitably. An example is Bridgestone which abandoned manufacture of an excellent range to concentrate on mainly tyres.
Two Stroke Performance (TSP) in Mornington, Victoria, is one of the very few remaining two stroke specialists. The small firm has only been in business a few years and was started to meet the demand from dedicated two stroke enthusiasts. They specialise in upgrades for KTM and Yamaha high performance dirt bikes. Dave McCarthy started the business as a dirt riding and engine modifying enthusiast who has developed from scratch the niche products which meet the demands of discerning buyers. The company even makes its own components and for cylinder heads that means machining the inner and outer parts from billet to precise dimensions. They adjust the combustion chamber, compression and squish to both improve and sweeten the output of high performing competition dirt bike engines – mainly KTM 250 and 300.