Source: Bike Bound
A Good Swift Kick in the Rear: MotoRelic’s 540cc 2-Stroke Minibike!
Ever heard of the Yamaha SRV540? If not, that might be because it was a high-performance two-stroke snowmobile that came out of Yamaha in the early 1980s. It had a forward-mounted engine, aluminum chassis, slide rail suspension, oil injection, and a fan-cooled 535cc twin tuned to 55 hp in order to meet horsepower regulations for competition in a number of racing circuits.
Yamaha marketed it with the slogan “How to take a good swift kick in the rear,” and the advertising copy claimed the SRV was ready for anything, “come hell or high mogul.” We don’t know much about snow machines, but that sounds like a good time to us!
Now we try not to play favorites here at BikeBound, but Sean Skinner of Virginia’s MotoRelic makes that very damn difficult because his builds are just so good. Back in ’22, he blew minds with his Yamaha Orange Krate — an XS650 inspired by the iconic Orange Krate edition of the Schwinn Sting-Ray muscle bike of the 1960s. Nostalgia overload!
Style for Miles: MotoRelic’s Yamaha XS650 “Adult Schwinn”
Once that bike was sold, Sean found himself itching for the challenge of creating another full-on motorcycle out of a design never intended for such. Riding down the lanes of boyhood memory, he came upon another nostalgia-inducing inspiration — the pull-start minibikes of yesteryear.
“As a kid, mini bikes were always in the stable. Either a Honda Mini Trail or some 5-hp friction brake mini bike deathtrap. While traveling down a rabbit hole of air-cooled snowmobile engines, I came across the 1982 Yamaha SRV540 engine. Pull start and nearly 60hp in a very compact assembly. Perfect for an overgrown ‘Mini-Bike.’”
Brilliant! But the challenges of putting a pull-start snowmobile engine in an overgrown, custom-built minibike would be many. These would include adapting the engine (designed for a CVT track-drive) to a belt primary + Harley 5-speed transmission + chain final drive, narrowing a Honda ATC200 three-wheeler front end four inches (and reversing it) with a custom triple and RD350 neck, coming up with the riserless bar design, building the entire frame itself from scratch with an appropriate rake and trail, fabricating the aluminum tank (part of which is hidden beneath the seat), making an expansion chamber (Sean’s first!) for the 2:1 exhaust, and much, much more.
Friends and colleagues joined the action with Wes Boege at Counterbalance doing up the seat in a Pirelli pattern to match the tires, Jeremy Cupp at LC Fabrications helping with the lower yoke, and Maryland’s Right-A-Way Powder handling the Whiskey bronze and Illusion lime powdercoat. The only paint on the bike is the Cerakote pipe — everything else is powder!
As you might imagine, this 535cc two-stroke “minibike” offers all the smoky, loud, nostalgia-scented fun any grown boy or girl could dream of — bravo!
“Luckily the 540 2-stroke is very easy to start and doesn’t require the strength of a rugby player. This bike is about how you would expect. Obnoxious on so many levels. From the exhaust crackle and smoke, to the open primary dry clutch noises, to the hand numbing vibrations at full RPM. It’s definitely a handful!”
Just our kind of fun! Below, Sean walks us through the nitty-gritty details of each aspect of the build, giving us an interior look into his methods and process. This is a truly special one, and hats off again to Sean for thinking and building outside the box — and pulling it off so well. Also, credit goes to Jonathan Thorpe (@jthorpephoto) for the photos. Enjoy!
Yamaha SRV540 Minibike: In the Builder’s Words…
So this build came about after selling the Yamaha Orange Krate build. I enjoyed creating a real motorcycle out of a design that was never supposed to be a motorcycle. As a kid, mini bikes were always in the stable. Either a Honda Mini Trail or some 5-hp friction brake mini bike deathtrap.
While traveling down a rabbit hole of air-cooled snowmobile engines, I came across the 1982 Yamaha SRV540 engine. Pull start and nearly 60hp in a very compact assembly. Perfect for an overgrown “Mini-Bike.”
I searched the trusty Marketplace and found a great donor sled in running condition. I got it home, removed the engine, and sold the good leftover parts to recoup the money spent on the sled. The engine was completely rebuilt with all new bearings, pistons and rings, and a fresh bore. All of the original engine parts were vapor-honed to leave a nice new aluminum finish.
The snowmobile uses a CVT for the track drive. On the crank there’s a nice tapered shaft to attach a BDL belt-drive pulley. I had my friend RTD FAB make an adapter to mate the two together perfectly. For transferring the power to the rear wheel I decided to use a Harley 5-speed that was donated to the project (Thanks Dave). I disassembled the trans to rebuild it and cut off everything related to the starter and other unnecessary tabs.
Once the engine and trans were back together and the belt drive was installed I fabricated a holding fixture to keep them together as a unit then welded that to my frame jig. That helped me keep everything in line when making all of the mounts from the frame to the engine and trans.
For the wheels I found a set of vintage Henry Abe wheels. The front is a Harley and the rear is CB750. Both are 16in. The tires I used are the Pirelli MT60RS 150/80/16. To me they had the perfect look for this build.
I thought way too long on what to do for the front end. Most mini bikes have a continuous “fork” from axle to handlebars. To get that look I used a front end from a Honda ATC200. I had to narrow the front a whole 4 inches to fit the Harley front wheel. I sweet talked Jeremy of LC Fabrications to help me with the lower triple that needed to be made to allow the 3-wheeler forks to play nice with the RD350 neck I used. Everything welded up like it was meant to be.
With the front wheel fitted to the forks I could figure out the rake and trail for the frame I had to build. I ended up spinning the fork lowers around to give me a leading axle and that let all of the measurements fall into place.
As for the bars, I really wanted the one piece fork to look like the mini but coming up with a riserless setup was interesting. I came up with a similar design like how a mirror threads onto a motorcycle. The lower part threaded into the fork tube through the upper triple and tightened into position with a lock nut. The upper part of the bars bolted onto those. This gave me the appearance of the “all one piece” I was going for. And a truly one of a kind front end.
The tubing arrived and I got to work on building the full-sized frame that would end up looking like a Taco mini bike. Getting the lines and proportions correct was tough, but all in all I think it really worked out great. Everything was TIG-welded into place. Since the rear wheel was CB750 I used the stock Super Sport rear caliper and rotor.
For the rear master, that is from a late model Sportster. I liked it because it has a built-in return spring and lever stop. That made it super easy to fab up everything. The foot controls are all handmade and the foot pegs are from Johnson Engineering.
Once the frame was off the jig and the front end was on, I got to work making rear wheel spacers and getting the rear wheel on. I have to say that I really lucked out with the engine and trans balance center lining up perfectly with the center of the rear tire. This made the drive chain and primary belt alignment incredibly easy. And made the bike very balanced. Take the victories where you can!
With the bike now as a roller I started on the gas tank. The aluminum tank is bigger than it looks. Most of it is hidden under the seat.
The seat was shaped up and I sent it to Wes at Counterbalance for some black leather. I requested the pattern of the tires be added to the seat. He absolutely nailed the Pirelli pattern.
This engine was designed by Yamaha to have a 2-into-1 intake and exhaust. I had to extend the intake to clear the trans and completely make the expansion chamber, something I have never done. The “header” part of the pipe was something I had to make flow around the frame all while keeping it equal lengths. As for the rest of the chamber I found an expansion pipe from a Polaris that was very close in dimensions. I proceeded to cut up the pipe and re-weld it to the angles and direction I needed it to go. Then the whole system was cerakoted black. The muffler is from HVC Cycles.
Besides the pipe there’s no other paint on this bike. All of the colors are powdercoat. And that was laid down by Right-A-Way Powder in Middletown, MD. Whiskey bronze on the wheels and Illusion lime time on the frame.
Pull-starting a motorcycle is not something normally done. Luckily the 540 2-stroke is very easy to start and doesn’t require the strength of a rugby player. This bike is about how you would expect. Obnoxious on so many levels. From the exhaust crackle and smoke, to the open primary dry clutch noises, to the hand numbing vibrations at full RPM. It’s definitely a handful! More fine tuning to come when the weather warms up!
Follow the Builder
Web: motorelic.com
Facebook: www.facebook.com/Motorelic/
Instagram: @motorelic
Photography: www.jthorpephoto.com | @jthorpephoto
More MotoRelic Builds
Pullstart Powerhouse: Yamaha SRV540 “Green Monster” – A Good Swift Kick in the Rear: MotoRelic’s 540cc 2-Stroke Minibike! Ever heard of the Yamaha SRV540? If not, that might be because it was a high-performance two-stroke snowmobile that came out of Yamaha in […] Big Bore 400/4: Honda “CB466F” Café Racer – 466cc Honda Cafe Racer from Motorelic… First available in 1975, the Honda CB400F (“400 Four”) showcased Honda’s technical prowess. Here was a miniaturized 408cc version of their larger fours, complete with café-inspired styling, nimble handling, […] Style for Miles: MotoRelic’s Yamaha XS650 “Adult Schwinn” – For Sale: An XS650 inspired by the ’68 Schwinn Sting-Ray Orange Krate! For many of us, the love of motorcycles starts with childhood pedal bikes. Not only is the bicycle the first taste of freedom […] Raptor Red Roadster: Kawasaki KZ1000 by MotoRelic – Sean Skinner of MotoRelic builds a red-hot KZ… Introduced in 1977, the Kawasaki KZ1000 would set the standard for generations of liter-size superbikes to come. The 1015cc engine boasted 90 horsepower in factory trim, good […] Dirt Road Ripper: Yamaha XT500 by MotoRelic – “Foot down and elbows up! Braaap!” The Yamaha XT500 is one of the most successful dual-purpose machines of all time, a big-bore four-stroke that proved itself in professional desert racing and on thousands of miles […] Backroad Warbird: Honda V30 Magna “WeeVee30” by MotoRelic – One of America’s most talented builders creates a bike just for himself… In 1984, Honda unveiled the VF500C, better known as the V30 Magna — a potent 500cc cruiser whose sophisticated V4 powerplant boasted technology […]
“}]]
