1964 Yamaha YA6 "Santa Barbara" 125cc Rotary-valve Single
December 1964 to February 1966
My first "brand new" motorbike.
In December 1964, my Dad could see that I was thoroughly hooked on riding motorbikes so he agreed to help me trade in my faithful old BSA on a brand spanking new shiny blue Yamaha YA6 125cc Rotary Valve single. For those who don't remember rotary valves, these engines were two-cycle (two stroke) and the transfer ports and exhaust ports were opened and closed by the piston as in a normal two-stroke. The difference was that the carburettor was mounted inside the crankcase cover where it fed through a rotary disc valve mounted on the end of the crankshaft. This allowed very precise and adjustable intake timing of the fuel-air mixture into the crankcase ... something that was just not possible with a "normal" two-stroke where the inlet port was uncovered by the lower skirt of the piston as it went upward on each stroke. This arrangement meant that a great deal more power could be wrung out of a small engine and that it had better fuel consumption than a regular two-stroke. The registration number was DC-895.
Here's the whole picture from which the one above was cropped. The YA6 is parked just near the bridge of Bridge Street Ballarat and one of Ballarat's historic old trams is lumbering towards us. Those were the days when the trams were our public transport running every few minutes, all day long, on about seven or eight different routes, instead of being confined to a short strip along the edge of Lake Wendouree on Sundays only. This shot was taken on 8th January 1966.
The Yamaha YA6 was the first model to feature Yamaha's dramatic new "Autolube" system. Two-stroke oil was kept in a separate oil tank from which a pump caused a steady but miniscule amount to kind of "ooze" into the bike's intake chamber (where the rotary valve was located). From the valve chamber it was carried into the crankase with the charge of fuel-air mixture where it lubricated the innards more by luck than management, just like any other two-stroke engine. The Autolube system meant that you never had to mix oil with the petrol and since the pump was controlled both by the speed of the engine as well as the throttle cable, it theoretically pumped in exactly the right amount to keep the engine well lubricated without the haze of blue smoke that followed the typical two-stroke in those days. In the picture at the right (click on thumbnail for a good view) you can see the layout of how the system worked. As the oil pump was critical to this system, the manual called for frequent checking and I soon became adept at tuning it very precisely, so that the engine was always well-lubricated but so that I never saw any blue smoke unless I pulled on the oil-pump cable with my hand to make it out-of-synch with the throttle cable.
Spark plugs and melted pistons:
The spark plug installed in the bike when it was new was made by NGK, a brand which nobody anywhere had ever heard of in Australia in those days. Every once in a while the plug would get bridged by a tiny bit of grit and when it did so, the bike would roll to a stop. Each time it only took a moment or two to pull out the plug, clean it and put it back and we were soon away again. However, I decided that it would be wise to carry a spare plug in my toolkit. I checked in the rider's manual and the only advice it gave was to fit an NGK plug. It showed pretty pictures of wet plugs, oily plugs, dried and blistered plugs and nice tan clean plugs and suggested which NGK plug should be fitted depending upon the condition of your original plug. I stopped at motor garages and most had never heard of a Yamaha. They could tell me what plugs to put in every model of BSA, Triumph, Norton, Indian or Harley, but a Yamaha was an absolutely unknown quantity. Eventually, in January 1965, I found a plug dealer somewhere who actually had the name "Yamaha" in his plug catalogue. The only models listed were "Twin" and "Single" and since mine was a single, I bought the recommended Champion brand plug. The next day, on Port Arlington Road near Point Henry, the original plug fouled, so I pulled it out and inserted the new one from my toolkit. As I crossed on a back road towards the Queenscliffe Road, I noticed that my motor was making a kind of "tinny" noise. A few minutes later, on the back road between Drysdale and St Leonards, the engine suddenly stopped firing but the normal engine braking effect was completely absent ... the bike just rolled on and on down the hill with the engine turning over but no sign of exhaust noise. I phoned my dad who was at Indented Head that day and he advised me to take the head off and look at the piston. When I did so, I found an enormous hole straight through the middle of the top of the piston. It turned out that the Champion plug was of the wrong heat range and that the "tinny" noise I had heard was called "detonation" and that the whole time that noise was present the aluminium of the piston had been melting away and getting blown out through the exhaust port and into the exhaust pipe which was now neatly lined with shiny aluminium. The bike was fitted with a new piston and I bought half a dozen shiny new NGK plugs of the correct heat range from Pratt & Osborne Motors in Geelong. I had learned an expensive lesson about two-stroke engines: they were extremely fussy about what kind of spark plugs you put into them.
About two-stroke oils:
The manual for the YA6 told me that I must never use any oil other than "Genuine Yamaha Autolube Oil" in my bike. Now I have a tendency to be a bit of a pedantic perfectionist when it comes to obeying manuals. However I soon learned it was impossible to purchase "Genuine Yamaha Autolube Oil" anywhere around the places I was likely to ride. Occasionally I was able to find "Two Stroke Oil" or "Outboard Oil" both of which tended to be outrageously expensive. My Dad told me that in his day, everyone with a two-stroke just added plain cheap old run-of-the-mill, ordinary, everyday SAE 30 oil to their petrol tanks and hoped they were adding the correct amounts. I decided that since Dad often knew what he was talking about, that I would try running the Yamaha on SAE 30 oil. It never missed a beat. I kept accurate records in a Shell Driver's Log Book of all the oil and petrol I bought and after a while I was able to calculate that the Autolube pump was doling out the oil at an average petrol to oil ratio of around 50 to 1, so it was certainly far more economical than mixing the oil with the petrol in the fuel tank. In retrospect, I realise that it was also very much more environmentally friendly than two-strokes running on premix, although nobody really thought about such matters back in those days.
Polishing the cylinder fins!
In those early motorcycling days, I always seemed to have a lot more time on my hands than I do today. A lot of this excess time was spent cleaning and polishing the little motorbike. The whole bike looked gleaming and shiny, but the fins on the cylinder looked kind of dull. Therefore I decided to polish up the outside of the cylinder. A television advertisement back in those days showed a bloke polishing his car (a street Hot Rod) engine with Johnsons Duraglo floor polish. I figured if it would polish the engine of a car, it could also polish the engine of a motorbike. Thus it happened that one day I "borrowed" my mum's can of Duraglo and took it out to the motorbike shed. For a couple of weeks, I did the same trick and you could see your face in each one of the fins of that engine. One day I had the bike at the local motorbike shop for some reason when the chief mechanic told me, "This engine is running too hot." He got down and took a squiz and exclaimed, "What the hell has happened to your cylinder fins?" I told him I had polished them to make them nice and shiny. He told me that the cast iron fins would radiate the heat into the atmosphere much more efficiently if they were not polished. I knew from the manual that the cylinder consisted of an iron sleeve pressed in to an aluminium barrel, but what he told me made sense when I thought back to my high school Physics classes. So then it was back to work using lots of elbow-grease to remove the Duraglo from the outside of that cylinder. Somehow it did seem to run consistently cooler after that. Another lesson learned.
Memories from the YA6 era:
This bike was the first one I was able to go longer distances on. Only half of
the capacity of the BSA but much faster and more reliable. The memories thinking of
this bike brings back are:
The YA6 was used to commute between my parent's home in Ballarat and my work in Traralgon and made frequent visits to Geelong and Melbourne as well as turning up in various parts of country Victoria on all sorts of odd occasions, so it ran up well over a thousand miles each month. And I started to get sick of a bike that ran so slowly. So it came about one day that we went to Pratt & Osborne Motors in Geelong where, after I had borrowed the money from my Grandpa, I purchased a shiny red and white Yamaha YDS3, registration number DH-528, if I recall it correctly.
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