Turning a YZ250 MXer into a YZ285 off-road missile

When you hear the name Wiseco you think naturally think of dirt bike pistons. But Wiseco does a whole lot more than just forge pistons at their Ohio plant. They forge clutch baskets, inner hubs, pressure plates and a whole line off-the-radar parts for the automotive racing industry. Wiseco also likes to build bikes, both moto and off-road, which brought us to Ohio, the Wiseco factory, the annual Turkey Run and the Big-bore Wiseco YZ285.


The heart of the Wiseco YZ285 is the motor. The modifications start with an over bored cylinder (to 71mm (285cc), then the cylinder gets replated with Apticote. The cylinder gets ported and power valves cut and massaged. The cylinder head then gets surfaced to adjust the squish pattern and compression. Max Power does the motor work and will tailor the modification to whatever type of power you desire. Of course the piston is custom made by Wiseco and the compression of the now YZ285 is much higher than stock. To smooth out the delivery of the increased low to mid, an MSR 11 ounce flywheel weight was bolted on. The good air in coming in flows through a Boyesen Rad valve and the used air out passes through an FMF SST pipe and Shorty Silencer. With the mods come more power and more heat, so a Boyesen Supercooler water pump kit was fit. In the clutch department, Wiseco fits their forged basket, forged inner hub, pressure plate, fiber plates, alloy plates and clutch cover.


Firing up the YZ285 is not a task for a weak right leg. The added compression equals stiff kick-starter action. Luckily out on trail the heavier flywheel weight helps reduce the possibility of stalling and having to kickback. We noticed a slight increase in vibration with the bigger piston, but it proved to be worth it with the enhanced power boost from low to mid. It’s odd that with the bigger slug and flywheel weight, top end power only mirrors stock, but again the increased roll-on and heavily muscled mid-range are incredible pluses to the powerband. For the woods of Ohio the motor mated well to the tight conditions. It can be lugged around right off idle and with the smooth clutch action the power is even more controlled. If you like hard hitting power the YZ285 delivers it with a twist of the wrist and a stab at the clutch. The YZ285 is down right explosive when prompted yet is a smooth operator when traction and control are necessary.

The suspension duties were handled by Pro-Action. They revalved front and back with custom valving and springs. The forks also received sub-tanks. We spent one of our days on the trail and on the motocross track working with Pro-Action to get a good balance for off-road plushness and mellow motocross duty. Quite honestly it was a bit stiff and felt too moto for the off-road terrain, though when pushed hard it rewarded the rider with a very positive ride.


The only thing we’d change on the Wiseco YZ285 is the 19-inch rear wheel. For off-road nasties the added sidewall of an 18 is a must. We’d also like if it were a little easier to kick but that might be because we are spoiled by a world blessed with push button starters on a slew of off-road machines. We’d also think it would look better in our garage and not in Ohio at Wiseco. We will be back in Ohio next year for an amazing weekend at the Turkey Run and hopefully Wiseco will have another great bike to battle with the trees. Check out to find out more about what they have your bike.




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