This story was originally published in the December 1976 issue of The Lap Times, the AFM’s official newsletter. Two-stroke fans might get a kick out of it.
Philippe DeLespinay at speed on the Garbage Can Special. Photo from (I think) Ken Mullins collection.
What is it, exactly? Some people think it’s a Yamaha TZ125, but Yamaha didn’t have a TZ125 in 1976. The eighth-liter race bike from Yamaha was a TA125, an air-cooled 2-stroke parallel twin. The TA125 was basically a hopped-up version of the RD125 street bike. Perhaps the GCS is a TA125 with a aftermarket water-cooling kit from somewhere in Europe. The bike has entered the AFM races as a “Mifuni 125,” racing in the 125 GP class. The owner calls it the Garbage Can Special. Whatever this bike is, it’s become the scourge of the 125 GP class, winning the last three races at Ontario Motor Speedway in 1976.
Water cooling is a big deal for a 2-stroke. Jetting an air-cooled 2-stroke motor is tricky. Jet it too rich and it doesn’t make much horsepower, jet it too lean and it overheats and seizes, or burns a hole in the piston. With water cooling you can watch the temperature gauge to guard against too-lean jetting and consequent overheating.
Intrigued by what appears to be a very different motorcycle, the Lap Times talked to the owner-rider, Philippe DeLespinay, to find out just what the bike is. It’s not a early-release Yamaha TZ125, nor is it a Yamaha TA125 with a water cooling kit. It is a well-thought-out, superbly-executed, home-built Grand Prix race bike. Practically everything on the bike is handmade or a modified production piece.
The center of attention is, of course, the engine. The crank cases are from a Yamaha TA125 but have been altered to accept different bearings with special retainers. The crankshaft also begins life as a TA125 part, but Hurley Wilvert does a number on it, reducing the overall diameter and fitting different crank pins and big-end bearings. The gearbox is still a 5-speed unit but some of the gears come from England, and all have been given a 5-degree chamfer to reduce weight and make engagement smoother.
The top-end is where things really get different. It’s still a parallel twin, but with a one-piece cylinder and water jacket, unlike the two separate cylinders of the TA125. The cylinder was designed by Philippe and sand cast in France, from where Philippe hails originally. The liners are cast iron, pressed in at a temperature of 400 degrees Centigrade. The bores as not chromed, as it’s easy to obtain cast iron sleeves and have them honed to match the pistons in case there is a drastic engine failure. The porting is typical piston-port style, developed by Philippe and Wilvert. Compared to the standard TA125 porting, the timing is less radical in the intake and exhaust and more radical at the transfer ports. Wilvert also built the expansion-chamber exhaust pipes, which are much shorter and fatter than TA125 pipes. The radiator is from a Kawasaki KR250 and the water pump, which is completely handmade, replaces the standard TA125 oil pump. With no oil pump the motor runs on old-fashioned oil-gas premix.
The cylinder heads are separate pieces that are recessed into the top of the cylinder jacket, instead of sitting on top TA125 style. The cooling fluid doesn’t pass over the heads but it surrounds them on all four sides for effective heat transfer. This feature allows fitting different cylinder heads without having to drain the coolant. This allowed DeLespinay and Wilvert to quickly try several different combustion chamber shapes during development.
That pretty much covers the engine alterations, and they work very well. The bike is intentionally run with slightly over-rich jetting yet it is still much faster than the standard TA125. The power band has been increased from 10,500 – 12,000 rpm to a very broad 10,500 – 15,500 rpm. The engine will spin to 16,000 without coming apart or seizing, and power is increased accordingly. Philippe claims the bike produces about 35 horsepower. If someone expresses disbelief at this number Philippe is quick to point out that the production Morbidelli 125s make about 37 hp, and the factory Morbidellis make nearly 40 hp.
[An aside: Morbidelli is an Italian firm that makes wood working machinery, but the 1970s owner was a motorcycle race fan and he also made a small number of 125cc race bikes for FIM (European) Grand Prix competition. Morbidelli is the only class-winning motorcycle in the long history of world championship racing that was not built by a motorcycle manufacturer, earning the 125cc championship in 1976 and 1977. The bikes and parts were nearly impossible to get in the U.S.]
You would think that having a reliable engine with more horsepower than anyone else in the class would satisfy most people. You could stuff it into a stock Yamaha TA125 chassis, hang the radiator somewhere near the front and have an instant race winner. Philippe and his pals don’t work that way – along with the custom motor are a host of chassis improvements. The frame began as a Jack Machin model from England, and then was altered to Philippe’s specs by C&J Frames. The front fork is a Cerianni unit with its internals replaced by Wilvert-developed pieces. The front wheel is built up from a machined magnesium hub carrying two unplated 2025-T6 aluminum brake disks. Brake calipers are from a Honda 500 four. The tires, front and rear, look like standard Dunlop K-81s, but are made with a racing compound on a racing carcass in Dunlop’s French factory, obtained through Harry Hunt.
Why does Philippe call it the Garbage Can Special? He likes to pretend he got many of his parts from the disposal bin. The original crankcases, brake calipers and radiator, maybe, but not much else.
It all adds up to a lot of hard work. Fortunately Philippe has had some help along the way. HTW Racing (Hurley Wilvert’s company) and California Cycle Center, both of Santa Ana, CA, have provided sponsorship. Harry Hunt donated tires and Bell Helmets has helped out. Even with the aid it’s clear that an enormous amount of time and talent has been spent on the project, and one begins to wonder, why so much effort for a few club race wins? Perhaps there will be a water cooling kit sold in the future. But talking with Philippe you get the feeling that he is not doing all this just to sell water-cooling kits to Yamaha TA125 owners. He likes to build motorcycles then win races riding them.
There is another possibility: the 125 project may have been a warm-up for the 250cc bike they are planning to build. The GCS is pretty trick and a fast 125cc bike, but wait until you see the 250cc version.
Postscript: To my knowledge the 250cc version of the GCS was never completed. Philippe is active on Facebook so perhaps he can add some comments to this page. According to sources on the internet Yamaha released the water-cooled TZ125 in 1979, making the GSC a bit less special. Still, Philippe got a three-year head start.