Variations on a theme
rear anchor is when you take into account all the attendant pivots, rods and linkages used to get the braking force from the right foot pedal over to the left-hand face of the rear hub.
The more I ride the YM the more it makes sense and within 20 minutes or so we’re getting on famously flying around the lanes of Hampshire. I’m revelling in the torque this oversized 250 is putting out and really getting the hang of the middle three ratios that suit what’s best described as ‘spirited riding’.
Top gear, fifth is effectively superfluous for today’s photoshoot simply because it’s so high. Just like many Japanese bikes right up to the early 1970s, top gear is effectively little more than an overdrive. Working that elderly 305 motor is unquestionably a pleasure not a chore but I am conscious of an ever-present roar and it’s not coming from those rakishly slash cut silencers either. Most of the decibels are coming out from under the seat as the primitive, pressed steel, air box rasps away at the country air.
The set up makes for an extremely loud drone that, over long distances, could have some serious impact upon your hearing; ear plugs are probably mandatory when riding YM1s!
Other than the bike’s deafening roar and its engine speed clutch it’s actually a remarkably relevant machine to ride even more than half a century after its inception. Its road manners are more than acceptable, its engine still eminently usable in modern traffic. Both the YM and its 250cc YDS3 brother neatly mark a transition period in Yamaha’s development of the seminal lightweight two-stroke twin.
Our bike in camera is effectively a generation on from the four-speed YD1 and YD2 yet just one of a series to run engine speed clutches. The bike also still holds true to its German ancestry with vertically split crankcases and this will still be the case for the next pair of 250s as well.
The subsequent YDS5 and YDS6
250s will both run similar engines but with clutches mounted in the more conventional location. Ultimately the YM 305 series were stopgap models until Yamaha had the resources to produce a true, full on, 350cc stroker twin. And as luck would have it we just happen to have access to one, so look out for what is possibly Yamaha’s most significant twostroke twin ever and one most CBG readers probably have never even heard of!
The YM1 landed in the States just as the street scrambler scene took off. Essentially road machines with dirt trail pretensions, the genre proved to be remarkably successful and all the major players swiftly jumped on board the gravy train.
Prerequisites included high bars (often braced), exposed suspension and the obligatory high pipes. Yamaha had been in the vanguard of the faux off-road movement with a raft of converted road machines culminating in the YDS3 based 250cc Big Bear, named after a famous American off-road race.
The bike proved to be a huge hit and so it was inevitable the YM1 would receive a similar makeover. The resultant YM1C sold well across the 1966 model year and apparently was used off-road, some were even brave enough to use it in competition!
1967 saw a visually similar YM2C that actually embraced a key element of the all new YR1 Grand Prix road bike. Although the engine cases remained vertically split the clutch was now on the layshaft which necessitated a seriously revised gearbox. If any bikes mark Yamaha’s transition from vertically to horizontal split engine cases it has to be both the YM2C (along with its street brother) and the YR1 350.
By 1968, street scramblers were becoming yesterday’s must-haves and Yamaha had a much more focussed dirt bike in the wings. Designed with huge American input the DT1 trail bike would be the final nail in the street scrambler’s coffin.