Lean, mean and green
Kawasaki’s advertising slogan in the Seventies made much of the light weight and colour of their MX models, we check out an SR400 which epitomised the advert legend.
Take one ex-works team Kawasaki, add a bit about the company’s early MX forays, talk about the work needed and hey, it’s an SR400 feature.
It is a fascinating world in which factory team bikes live, and there are three separate elements to that world. Naturally there’s the race day, then there’s the paddock fettling sessions where minor and occasionally not so minor faults are repaired and things get checked over between races, and then there’s the factory race shop where the machine is built in the first place. The hallowed ground with locked doors and blanked out windows being accessible only to a favoured few – at least that’s what we like to believe.
Once their race life is over, these bikes generally head back to the factory, rarely to be seen again unless, as in this SR400’S case, it comes to an enthusiast who appreciates it for what it is.
Given the level of reworking owner Clive Bussey has done on other machines of his we’ve featured, we thought this one must have been almost too easy. “Well, not quite,” he grins, “but the hardest job was the frame as it’d been altered at the rear and was bent in three places.”
What Clive did was to remake the whole rear end to correct the damage and restore the chassis to its late 1974 spec.
“I know from information I got with the bike that this is the new frame which Christer Hammargren tried for the British MX GP in 1974. The engine positioning is slightly lower than previous versions and it’s also got reed valve induction.”
Clive also found the frame was constructed from lightweight chrome molybdenum tubing which had been TIG welded together – the whole bike is a curious mix of stock factory parts with specially fabricated bits and pieces here and there.
One of the trick bits was up at the front end where the factory had used magnesium Marzocchi forks, and it wasn’t only Kawasaki who used such suspension either as Suzuki used them too. However, for the rear end it was Germany’s Bilstein gas units which soaked up the rough tracks of the GP circuit. Clive also found the front hub and plate were pretty much stock items while the rear was similar to stock but sandcast magnesium for a greater weight saving. In fact this attention to weight is clear throughout the whole works bike thing as time and trouble has been taken to hollow out bolt heads, drill through spindles and shave valuable ounces off here, there and everywhere.
The SR400 engine was a slight drop back from the 500cc versions, which rumour has it were interesting to ride, and the slightly smaller capacity was decided on with a nod to the buying public who might not have the ability of the works team member.
In any case, what Clive found when stripping the bike was all the internals were in excellent order and he admitted breathing a sigh of relief over this as he said “there are a lot of special parts inside the engine even though the cases are stock, internally it was so good I feel it might well have been rebuilt late on in its race life and then done very little work afterwards.”
This thought is borne out by the top fin of the barrel having ‘Lux GP’ written on it in felt pen and the Luxembourg GP was the last one of the season in 1974.
Though the world was heading towards standardising gear changes being on the left-hand side, for a factory machine a rider could request the right-hand side and that’s what Hammargren did.
The cases themselves are stock ones but they house a one-off crankshaft on top of which is a special piston matched to the induction pulses of a reed valve system used for the first time at the British GP. The barrel and cylinder head are special works type versions as is the five-speed gear cluster in the box.
To match the power of the 400cc engine, the Kawasaki carefully chose more appropriate ratios to give their man as good a chance as they could. Also helping keep the bike driving properly is a billet clutch machined from solid. Providing the sparks is an electronic ignition system specifically created for this machine. The carburettor however, is a stock Mikuni and would have been used in the day, though it’s not the original one as far as Clive knows. “In the end all I really needed for the engine rebuild were new gaskets and seals so it all went together easily.”
An engine of this size being belted round a MX track in an international event gulps in quite a bit of air to help the fuel burn and the airbox is a large capacity one so there is always enough filtered air going in to the
carburettor. It is topped off with a lightweight seat and an interesting green glass fibre fuel tank. Interesting because at that time on road bikes in the UK glass fibre was banned from road machines as there were horror stories of badly made, large capacity café racer petrol tanks exploding in crashes. Properly made by someone who takes the time to do it right the material is excellent and stands up well to the rigours of racing. Even so, just to be on the safe side this one has been pop-riveted around the seam to provide an extra measure of security.
As I looked the Kawasaki over, Clive kept pointing out various little details which go in to making an excellent restoration rather than an average one. For instance, the rear brake on a standard bike would be cable operated, but on the works bike it’s a rod which requires a slightly different way of working. Then there’s the cables with aluminium ferules and adjusters over the stock steel ones… Luckily new cables were among the stock of spares which came with the bike. I gave the bike one final glance and realised I’d not asked the most obvious question of all… with Kawasaki MX bikes having the initial KX how come this is an SR? “It’s a code all works bikes have, SR = Special Racer.”
Ah, okay, question answered and yes, it is a special racer and it laid the foundations for Kawasaki to win world titles a few years later.