MGP YAMAHA XS500
Launched in 1972, the Yamaha TX500 was a hefty street bike. So how do you turn one into a Manx Grand Prix winner?
Sometimes a solution is staring you right in the face, but it takes someone else to quietly point it out to you. That’s precisely what happened when John and Colin Davies were looking for a machine to replace their Honda CB350K4 and CB500/4 race bikes that had reached the ends of their development.
“We’d been running the 500/4s for a few years,” says John. “They were never enough to beat the £80,000 Patons. Then a friend in The Isle Of Man looked at a Yamaha TX500, and said it might be just the thing you’re after.”
And so it proved. Last year’s Classic Senior Manx Grand Prix win for Lee Johnston on the Davies Motorsport Yamaha TX500 showed how a portly, unsung 1972 road bike could be transformed into a race winner. Johnston beat Stefano Bonetti (Paton) by eight seconds over a three-lap race – and set a fastest lap of 111.029mph.
That 2022 Manx win was the culmination of rigorous development work, meticulous preparation and Lee Johnston’s prodigious skills. Untapping the dormant potential of the TX500 was Colin Davies’ task.
“With double overhead cams and four valves per cylinder you’ve got a good start point,” says Colin. “But it’s a heavy engine – or at least it was when we began the work.” Colin, who kicked off his illustrious career servicing fruit machines, has worked with 250 Grand Prix winner Martin Wimmer, then Ron Haslam, Niall Mackenzie, Kevin Schwantz, Scott Russell and Team Roberts. It wasn’t until he teamed up with Glen Richards and latterly Alex Lowes in British Supersport and Superbikes that he got to work on four-strokes.
“Finding the horsepower was tough,” he says. “We started out with just 52bhp.” With a good Manx Norton making more than 60bhp and the exotic Patons producing around 75bhp, they were nowhere near being competitive. After four years’ hard graft their engine now delivers 71bhp.
Yamaha engineered the TX strong: “Really strong, the crankcases are way overengineered,” says Colin. The 180º crankshaft runs on three main bearings [all shell, like the big-ends] and a balancer shaft is chain-driven from the left side of the crank. Yamaha’s Omni-Phase Balancing System proved effective [if hard to service] for road riders, bu
