It would be difficult to write a technical article on any of the Yamaha twin cylinder production racers without mentioning their road going cousins. In more recent time, the link may have been more for homologation purposes but initially it was a necessity.
The first real over the counter production racers, the 1962 TD1s, were based on the YDS2 sports 250 which itself was the second generation of the highly popular sports bike the YDS1 The YDS2 featured many improvements over its predecessor but not just in a few design details, but everything from the handling to performance and reliability factors and the TD1 gained Yamaha’s most up to date technology from a road bike. In reality, the YDS2’s improvements were gleaned from lessons learned from the Japanese premier event winning machines, the YDS1 Asama racers and the road race variant the factory RR250s or YZ24 250S.
This model was the direct descendent of Yamaha’s own original racing design philosophy; piston ported, air cooled twin cylinder engine which was fitted into the frame of the disc-valve RD48 works twin which was not, as so commonly written, a lighter gauge tube version of the YDS2. The disc valve technology used in the works bikes incidentally was brought in from Showa, who quite obviously had studied the Suzuki version of Ernst Degner’s MZ design when Yamaha bought them out.
The TD1 shared the YDS2’s engine layout and the following mechanical parts were employed:-
crankcases, crankshaft, clutch [with upgraded friction plates and springs], primary gears, gear change mechanism, gearbox shafts and some gears.
Other parts were unique to the TD1 engine:- high compression heads, chrome lined alloy barrels and twin ring pistons with reduced crown diameter to reduce the risk of seizure.
Mitsubishi MC-2RY magneto, Mikuni-Amal remote float carburettors were unique to the racer and alloy engine castings were sandcast in small batches. For reference and as with all the TD1s, the cylinder heads were smaller in diameter than the road going YDS2s and they featured an extra smaller external fin. So, if you try a road going cylinder head on a race barrel it will fit the studs but overlap the barrel, but if suitably modified, can still be used. Whilst the full production race TD1 was marketed, a race-kitted YDS2 was also available, designated YDS2R, as was a Scrambler, the YDS2CM, and an American only flat track racer the YDS2M Ascot Scrambler which featured a full TD1 spec.
The U.K. initially was issued with 2 TD1s which were delivered in time for the 1962 London Motorcycle Show where Geoff Monty became the 1st official Yamaha dealer, closely followed by Basil Keys of Worthing. The bikes proved to be a popular attraction at the show and Monty received one firm order there and then and which materialised into the U.K. in early 1963 and went on to be the first Yamaha to win a race.
The model was soon updated in the form of the TD1A in 1964. The TD1A was again based upon the YDS2 and was still advertised as the TD1, but it was in fact a very different machine to the first TD1. It featured a new frame, new forks, new yokes, new steering damper assembly new front mudguard, new tacho and bracket.
Essentially the complete chassis was totally uprated; this could well have been to improve production techniques. Whereas the orange red fuel tank of the TD1s had white YAMAHA lettering the TD1A had gold lettering. The engine remained mostly unchanged although pistons were updated to single ring and the bores were now anodised and new exhausts were fitted based on pipes trialled on the works TD1s raced at Suzuka in 1962 although the brackets now fitted on a separate mount of the footpeg mounting loop. The magneto featured a small upgrade to the MF-2RY. Just 16 TD1A machines were imported into the U.K. most notably going to Geoff Monty, Franco Sheene, Ted Broad and Roy Boughey.
By the end of 1964, the TD1A was replaced by the TD1B. The 1B’s engine, well the crankcases, crank and the gearbox basics were based on the new road model YDS3. The crankshaft featured a larger diameter boss on the clutch end and larger, more substantial conrod needle roller bearings. The race only engine parts were also uprated to suit the new crankcases. The cylinders still had the simple three port configuration and featured wider spread mounting holes to suit the wider spaced porting, as did the heads which also had reinforcing webs on the underside to reduce cracking.
The pistons now had the skirt length reduced and a 1mm skim was removed from the exhaust side of the piston crown to improve the timing. New wider diameter expansion pipes were fitted giving a marked increase in power at the expense of a more defined power band. The primary gears were now specific to the TD1B and were straight cut and to a ration to suit the race only machine. Gear ratios were also uprated to suit the new power characteristics, magneto and carbs remained the same at this stage. Initially the chassis and running gear were the same as the TD1A.
The TD1B was uprated for 1965, this time mostly cosmetically. A new more streamlined and white, fuel tank was fitted, along with a new seat. A heavier gauged swinging arm was fitted, along with locating lugs to locate the chain adjusting cams. In 1966 the 1B was again uprated. New slightly beefed up forks with an alloy top yoke, an improved M200 type magneto, painted expansion pipes with sprung mounted brackets replaced the old chrome units.
The carburettor float chambers were now hung from a bracket on the frame under the fuel tank, instead of the rear of the engine. Incidentally, in line with the new production techniques, the crankcases were now smooth die-castings instead of being sandcast parts.
By 1967 the YDS3 was replaced by the new and much improved YDS5. The YDS5 received a ‘proper’ clutch that was mounted on the gearbox input shaft. This was the biggest bugbare on the racing machines, and hence the TD1C was seen as a major improvement over the TD1B. As well as the clutch, the barrels were now fitted with five ports, receiving extra ‘S’ shaped boost ports in the cylinder walls to increase power delivery.
The TD1C became popular worldwide, with countless wins and lap records. In fact Yamaha used a works TD1C in some events in the Far East. Carburettors and magneto remained the same as the previous model, being the M200-02. Cycle parts were deemed good enough and remained the same as the last of the TD1Bs but in reality, the chassis was on the limit for the 40+ bhp engine and many machines soon received reinforcing strut bracing, aftermarket forks and suspension units, in order to gain some stability.
This led to many home grown privateer tuners to develop their own frames such as Ted Broad and Jim Lee in the U.K.
Article courtesy of Richard Tracy (www.ydracer.com)