Photo: Purpose Built Moto
Essentially, the versatile Yamaha SR platform is to a custom motorcycle builder what a blank canvas is to a gifted painter.
Upon meeting the bike-modding artisans over at Purpose Built Moto (PBM), this 1978 Yamaha SR500 was in dire need of some TLC. The mid-sized classic had been owned by the same family since the early eighties, but its air-cooled 499cc thumper stopped working once the odo reached 80,000 kilometers (50k miles). Mark and Jon Mitchell were determined to give it a second chance at life, though.
The father-and-son pair pitched their vision to PBM frontman Tom Gilroy, and things got underway in the early days of 2022. After a complete teardown, the Aussies busied themselves with an all-inclusive powertrain overhaul so as to not only get the SR500’s single-cylinder mill in working order, but make it perform better than it did nearly half a century ago.
For that to be achieved, they ported the cylinder head and fitted a new clutch mechanism, premium valve springs, and a high-compression piston. Additionally, the motorcycle’s stock carb was swapped with a higher-spec Mikuni Flatslide module, while a session of hydro-blasting got its engine looking nice and pristine on the outside.
As per their client’s request, Tom’s squad retained the donor’s standard wheels, but had them hydro-blasted, clear-coated, and ultimately cloaked in sport-touring Angel GT rubber from Pirelli. Next, they performed a good bit of frame surgery at the rear end, trimming and looping the bike’s subframe in preparation for a custom Brat-style seat.
Beneath the flat saddle lies Purpose Built Moto’s proprietary Black Box control unit, which enabled them to simplify the SR500’s wiring. Moreover, there’s a handmade aluminum fender attached to the rear skeleton, along with dual-function LEDs and an inconspicuous license plate bracket. All this equipment is supported by top-shelf YSS shocks with chrome-plated progressive springs.
Up north, the original forks are still in play, but they’ve been rebuilt inside out and stiffened up in the process. The following step involved the fabrication of a bespoke exhaust system to replace the stock pipes, and the final product consists of a high-mounted header terminating in a reverse megaphone silencer on the right-hand side.
Peek up at the cockpit area, and you’ll be greeted by a Biltwell handlebar equipped with stealthy grips, Accossato control levers, and PBM switchgear, as well as a Domino XM2 throttle and underslung mirrors. The standard dials were ditched to make room for Daytona Velona instrumentation, while the factory headlamp got rebuilt and fitted with tiny aftermarket blinkers.
A slim fender rounds things out at twelve o’clock, and the gorgeous finish covering the creature’s bodywork was executed by PopBang Classics. For the finishing touch, Tom’s experts had a thin stainless-steel rod welded onto the lower section of the factory gas tank, thus adding a bit of pizzazz to the SR500’s mostly muted aesthetic.
The father-and-son pair pitched their vision to PBM frontman Tom Gilroy, and things got underway in the early days of 2022. After a complete teardown, the Aussies busied themselves with an all-inclusive powertrain overhaul so as to not only get the SR500’s single-cylinder mill in working order, but make it perform better than it did nearly half a century ago.
For that to be achieved, they ported the cylinder head and fitted a new clutch mechanism, premium valve springs, and a high-compression piston. Additionally, the motorcycle’s stock carb was swapped with a higher-spec Mikuni Flatslide module, while a session of hydro-blasting got its engine looking nice and pristine on the outside.
As per their client’s request, Tom’s squad retained the donor’s standard wheels, but had them hydro-blasted, clear-coated, and ultimately cloaked in sport-touring Angel GT rubber from Pirelli. Next, they performed a good bit of frame surgery at the rear end, trimming and looping the bike’s subframe in preparation for a custom Brat-style seat.
Beneath the flat saddle lies Purpose Built Moto’s proprietary Black Box control unit, which enabled them to simplify the SR500’s wiring. Moreover, there’s a handmade aluminum fender attached to the rear skeleton, along with dual-function LEDs and an inconspicuous license plate bracket. All this equipment is supported by top-shelf YSS shocks with chrome-plated progressive springs.
Up north, the original forks are still in play, but they’ve been rebuilt inside out and stiffened up in the process. The following step involved the fabrication of a bespoke exhaust system to replace the stock pipes, and the final product consists of a high-mounted header terminating in a reverse megaphone silencer on the right-hand side.
Peek up at the cockpit area, and you’ll be greeted by a Biltwell handlebar equipped with stealthy grips, Accossato control levers, and PBM switchgear, as well as a Domino XM2 throttle and underslung mirrors. The standard dials were ditched to make room for Daytona Velona instrumentation, while the factory headlamp got rebuilt and fitted with tiny aftermarket blinkers.
A slim fender rounds things out at twelve o’clock, and the gorgeous finish covering the creature’s bodywork was executed by PopBang Classics. For the finishing touch, Tom’s experts had a thin stainless-steel rod welded onto the lower section of the factory gas tank, thus adding a bit of pizzazz to the SR500’s mostly muted aesthetic.
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