Small, But Perfectly Formed
Words: Dave M
Photos: Dricot Thierry
Anyone who follows the world of custom motorcycles with any kind of passion and enthusiasm (or maybe, like me, is just an anorak) will know the name of Krugger.
It's a nickname, and it belongs to Fred Bertrand, the acclaimed Belgian bike builder and double AMD world champion of custom bike building. Fred's built a number of ground-breaking customs over the years, and his latest build was as individual as any of them. Taking a different approach to his normal builds, this one was in collaboration with Yamaha Europe, when they asked him to build a bike from their current range – one that would fit in rather neatly with their Yard Built programme.
However, Fred side-stepped the Yamaha drive for promotion by picking a bike from the Yamaha range that is somewhat different to the water-cooled twin and triples picked by other builders, as it isn't an MT-07 or MT-09, nor is it a vee twin cruiser, but it's the oldest bike in the current Yamaha line-up, although how much longer it remains in production is something of an uncertainty thanks to ever-tightening emissions rules. The model in question has been in production for decades, first joining the line-up in 1978! Fred chose the SR thanks to its simplicity – not only in that it's a single cylinder engine, but also in that it doesn't have all the electronics that most modern machinery comes with. Okay, so the current SR has fuel injection, but Fred was going to do away with that anyway...
Compared to some of Fred's previous builds, the Yamaha was fairly straightforward, using the original frame, forks and wheels, while the engine remains fairly standard. Well, internally it does, but there's quite a serious modification to the induction side of the combustion process...
Having hurled the fuel injection as far as the confines of his workshop would allow, Fred set to joining together a 48mm S&S carburettor, some stainless tubing, and great big eff-off bellmouth and an ever-so-dinky Aisin 300 supercharger. The 'charger is the type that Subaru use for some of their smaller cars, and it's driven by a belt running from the left-hand side of the crank, neatly tucked above the output shaft and sprocket. Unusually, Fred has the 'charger inlet pointing forward - which makes for a really nice placement of the carb, pointing forward and into the airstream – but results in the 'charger's outlet, which strictly speaking needs to go into the inlet ports as directly as possible, having a 90º bend. Although this does look exceedingly cool... The other side of the combustion process sees a bespoke stainless steel exhaust built to follow the lines of the frame.
While the frame is that with which the bike left the factory, Fred has modified it somewhat, clearing up the junction with the steering head and removing any unnecessary brackets and lugs, and creating a new rear loop for that diminutive seat unit. The ultra-slim profile has been achieved by cutting the standard tank down and narrowing it so that it sits on top of the frame's twin top rails, although it has also been lengthened for the cafe racer look. That tiny tail unit somehow manages to hide all the electrical components for the bike, although with the loss of the fuel injection there'll be far fewer things to hide!
The wheels, brakes and forks are all standard, although the forks have been lowered, and a pair of Fox shocks fitted at the rear give a balanced stance. The top yoke has been modified, and a pair of one-off bars (can a pair be 'one-off?) hold Beringer master cylinders and Motogadget switchgear.
Unusually, Fred wasn't alone when he made the decisions on the modifications for the little SR, for he worked alongside Bernard Ansiau, a fellow Belgian and a MotoGP mechanic who has swung the spanners for loads of world class racers, including Mick Doohan, Kenny Roberts, Wayne Rainey and, currently, the Doctor himself, Valentino Rossi. Between the two of them, they wanted to give the little cylinder a feeling that it was somehow connected with Yamaha's motorsport heritage, and it's no coincidence that there are visual similarities to the early TZ race bikes. And, of course, there's that Yamaha speed block-style paintwork! And you'll notice that the blue blocks in the paint also contain lots of names. They're all riders that Bernard has been involved with in his long career, and there's a special light-hearted homage to Valentino under the back seat... Another subtle nod towards racing is that the bike wears Dunlop K81 tyres, which are based on the pattern of the first tyres to lap the Isle of Man TT course at an average speed of 100mph, although they are made in a modern compound.
The SR400 (and it's 500cc brother) is hugely popular in Japan and, with builds like the Krugger supercharged SR, you can bet that there'll be more people elsewhere on the hunt for one to use as a project...
Yamaha SR400, Aisin 300 supercharger, one-off stainless steel exhaust, one-off plenum chamber, S&S 48mm carb.
Yamaha SR400, welds tidied, modified at headstock, new rear loop.
Standard lowered forks, standard wheel, disc & caliper, modified top yoke, one-off bars, Beringer master cylinders, Motogadget speedo & switchgear, Dunlop K81 tyre.
Standard swinging arm, wheel & drum brake, Fox shock absorbers, Dunlop K81 tyre.
Modified SR400 fuel tank, custom tail unit & headlight cowl, RG500 style front mudguard.
One-off loom, all electrical component in tail unit.
Paint & polish:
Blue & white Yamaha Speedblock design.