Small but well formed

You’re going to get that dirty? Well, yes, that’s what we do…

A good-looking 125 Yamaha catches the editorial eye at the International Dirt Bike Show. Its story is quite intriguing.

Afew years ago a colleague who is not really au fait with the ins and outs of the dirt bike world, was incredulous at the thought that someone would build a great-looking motorcycle and then pit it against the filthiest conditions possible. I was equally incredulous to think someone wouldn’t do just that as, after all that is sort of the point of the whole thing isn’t it?

You understand what I’m talking about though don’t you? The care taken washing the bike, the fettling session, the cosseting and then, at the track, winding it on with no thought but being first into the corner and passing your mate – whether you are fighting for first or second place or 21st or 22nd place – maybe wondering whether another bhp could be squeezed out of the engine with an update or a special part… we are actually all the same in that respect. It doesn’t matter whether our sport is the feet-up version or an enduro or an MX, a well fettled bike is always the aim.

While doing the circuit of the Central Wheel International Dirt Bike Show at Stafford County Showground last year, there on the National Twinshock and Evo MX stand were a couple of very smart Yamahas – this 125 and a 250 too. The bikes belong to regular racer Jim Shand and they were seriously well sorted. The 125 intrigued me because it didn’t look like I remembered them to look when

I was reading the press of 1980. I’ll allow at that time I was totally focussed on trials riding, with MX something I read about rather than being involved in. I did recall something being written at the time that said Yamaha had ‘mirrored’ the engine from the previous year. For 1980 the engine was still air-cooled as before, but the drive had been swapped over to the right-hand side rather than on the left, as in previous years. There appears to be no reason for this, other than ‘because we can’, though having discussed such things with people involved in other areas of Japanese thought, there will have been a reason for the swapping over and it might have involved needing to prove something or perhaps something somewhere needed testing out for a future project that might not have any motorcycle connection at all, but there you are.

When I caught up with Jim he confirmed things were not as they should be. “I bought the bike to use and race,” he says, “it was running too, but everything was so worn out I’m not sure how it was running.”

When presented with such a situation it focusses the attention – there’s no ‘will I or won’t I’ about it, as everything has to be done. “I’ve seen some bikes which needed work,” Jim tells me as we scoff Darren Hudson’s biscuits, “but this one raised an eyebrow.” First to go were the plastics. “I could have had them refurbished, but the cost of doing that was more

than the cost of putting new ones on and it gets even more cost effective if you’re not tied to originality.” With later plastics and seat in place the bike looks a lot different to the standard version, and just for the record I think either version looks fine, but this is Jim’s bike...

With the bike in bits in his workshop, Jim took a look at the frame and worked out what would need to be altered to fit an Öhlins shock. They might look similar to the standard set-up, but subtle differences meant a few brackets had to be altered on the subframe. All other surplus brackets have gone and this saves an ounce or three of course, but it also tidies everything up. The swinging arm has bushes and bearings in and they have to go together in a particular way – as we found out with our similar year IT465 – or nothing fits. It’s not hard to change the bits, though a little warmth helps things along.

Taking the engine apart it was clear that more replacements were needed. The big-end was worn out so the crank had to be split and a new conrod kit fitted. Further up the engine, though Jim didn’t say the exact words, I got the impression a finger rather than a feeler gauge could be pushed down the side of the piston and a rebore with a well-oversize piston was the only option. Do we even need to say that all the bearings were well past their sell-by dates? Well, they were, so every one was replaced, seals too. 

There is no doubt this 125 YZ is a smart machine.

1 1: Öhlins rear shocker needs a remote reservoir to allow for gas and oil expansion and cooling.

6 6: Big holes in the side of the airbox help the engine breathe, especially as a 38mm carb has been fitted instead of the 36mm standard one.

3 3: Plenty of room here for the suspension movement.

2 2: Raptor footrests are a popular fitment, as boots don’t slide off so easily.

7 7: This is the last year of the air-cooled engine, water-cooling was the way forward.

5 5: Tank mount protects from vibration problems.

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4 4: The electrics are easily accessible.

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8: For some unknown reason Yamaha reversed the layout of the 125… the drive went from the left to the right… then a bit later they redesigned the motor to water-cooled spec… 9: Re-packable silencers are a godsend to two-stroke racers. 10: Some parts are difficult to find, but Motokiwi in New Zealand has reproduced such things as flywheel cases.