BY: Séan Hendley
PICS: Erwin Minnie & Zac Botha
Yeah, you read that correctly a 500cc two stroke Yamaha motocrosser built into a 2012 model YZ, with the latest chassis and suspension. The answer to the question is…. YES, YES, YES, YES!!! OH GOODNESS, (or insert your preferred expletive here), YES.
We heard talk of such a legend and went on a mission to track this Unicorn down. Our mission took us to the doors of Shimwells Yamaha in Boksburg where Zac Botha confirmed the existence of said fabled machine which belongs to one Mr. Gray Dick, who we suspect does intend to ride it a bit competitively here and there.
It started out life as a fairly decent 2012 Yamaha YZ250 2 stroke MX bike and for the most part it still is…. except where it really matters – THE ENGINE, (which surprisingly still retains some of its original parts), and is where 99.9% of all the changes happened. Canadian company BRC Racing develops and manufactures 500cc 2T engine kits. From what Zac tells us, anybody with reasonably proficient mechanical skills and a decent set of tools can actually build one of these in their garage at home, that is how good the kits are. The thing is though, they are not cheap especially with our wobbling currency. Depending on the exchange rate, shipping costs, import duties etc you’re looking at somewhere around 100k to 150k and that is just for the kit…. you still need to get the bike. But here there is a little bit of a reprieve, you don’t need to lash out another R120k odd for a new machine, Zac tells us the kit bolts into anything from a 2002 model onwards, (the steel chassis bikes do require a minor modification – but nothing too serious), however the preferred models are the Yamaha’s YZ 250’s from 2005 and upwards when they changed to the aluminium chassis.
Other than the sub frame, tank and plastics there has been almost no change to the 2T YZ’s from then to now. A pretty severe case of “If it ain’t broken, don’t fix it”, we just don’t understand why Yamaha hasn’t updated it with a happy button and a bigger piston with fuel injection.The stock Kayaba suspension and chassis as well as the clutch and one or two other bits and bobs are still considered to be exceptionally good and will easily handle all that extra power and still handle extremely well – we are told.
The beauty of this conversion, with all the love and nostalgia around 2 stroke bikes, especially big bore 2 strokes is that this uses standard modern OEM chassis, brakes, suspension and bolts in a brand new, (not a rebuilt or refurbished), OEM quality new 500cc engine with some lekker modern upgrades. So you know it is going to be reliable and rideable.
As mentioned, this particular machine is a 2012 and the team at Shimwells completely refreshed and rebuilt absolutely everything that remains of the original bike just because it seemed the proper thing to do. They then themed it with the latest 50th Anniversary edition body kit and graphics as well as the funky purple wheels, new tank and sub-frame to bring it right up to date. So if you have an old ‘02 and onwards, and especially an aluminium chassis model YZ lying around, still in reasonably good nick gathering dust in your garage and a spare R150k cash banging about, this might be a fun project.
What is all in the kit and what engineering mods do you need to do?
Well as far as mods are concerned, it is pretty much nothing if you buy the BRC radiator. If you decide to use your old radiator, then you have to relocate your inlet and outlet pipes which requires a bit of cutting and welding, and there are so many professionals doing it for fairly cheap here anyway. What makes this BRC kit so lekker is the fact that everything bolts directly onto the standard YZ chassis using all the original factory mounting points without any modifications whatsoever. The kit even comes with a full FMF exhaust system that uses all the same mounts as the standard unit.
We did ask about an electric start which BRC does claim bolts straight on but that would be an extra R35k odd depending on the exchange rate, this bike only has a kick start. We hear your warnings of 500cc 2T’s of old being violent on shins and calf muscles when kicked into life, but that has been sorted with quite a special decompression valve which you engage manually via a button, let it go and kick start like normal, as soon as the engine fires up the decomp valves disengages, how cool is that?
This is a very serious bit of tech once you get inside the engine. They have used inspiration from Honda’s CR500 beast to design this kit. So the piston, the conrod and ancillaries, the crank, the casings, the cylinder head, the decomp valve and the power-valve are all BRC developed, designed and manufactured and all work together as a proper OEM unit with OEM reliability.
HOKAAI….!! HANG ON JUST ONE MINUTE…!!! Power-Valve – REALLY? Yup, that’s correct, a simple, pneumatic power valve system for linear, smooth power delivery and added bottom end performance. BUT WAIT – THERE’S MORE! Big Bore 2 strokes were well known for buzzing and vibrating bedonerd. BRC have sorted that all out with an integral counterbalance shaft, really smoothing the 500cc out and making it more rideable. C’mon – Tell us you don’t want one now?
How many more times can we use “cool” or “lekker”? Well, watch this space! A particularly cool feature is the fact that your existing gearbox, clutch etc. fits straight into the BRC casings without any extra engineering needed. You also use your standard electrics loom, flywheel and stator coil as well as pickups. BRC have designed their kit to work off the standard YZ 2T spark timing and even your standard 250 2T carb with some adjustments to the jetting (obviously). Even the standard air-box and air filter are used without any modification, lekker man…. LEKKER.
Our next question was: “Surely, with all the extra torque and power you would need to weld a bunch of braces and gussets onto the chassis to stop it from twisting and flexing??”. Again – not, BRC reckons that the YZ chassis is that good that it doesn’t need any modifications at all, neither does the suspension, nor the braking system, nor the pivot point bearings or linkages – NADA! It even uses the same spark plug.
Now the question on everybody’s lips is – How strong is it? Well according to the BRC website you can expect “Explosive motocross power delivery with around 60 plus horsepower and somewhere just shy of 70 newton metres of torque all tailored for all out motocross”. Around 60 Hp and 70 Nm on a 2 stroke dirt bike, that’s going to get a grin on your dial. The guys at BRC seem to have really thought this through properly.
Yes, the cost does seem a bit eye watering, especially if you add in the electric start, (which quite frankly – you should), but when balanced against the price of the latest big bore 2T bikes on the market at the moment it really isn’t too terrible, especially if you have a good donor bike lying around that has already shown a return on investment over and over again.
Maybe this will revive 500cc 2T racing in this country. We believe there are 2 other of these YZ500’s floating around and used regularly in racing, with one down behind the Banana Curtain in KZN and one other side the mountain in the Cape.
If you’re keen, chat to Zac at Shimwells Yamaha.
