Clean Your Snowmobile's Exhaust Valve

Nov. 12, 2007 By Tony Severenuk

What is a Power Valve (a.k.a. VES, RAVE)
Two stroke motors are very simplistic compared to their four stroke cousins, but simplicity does come with a price. A two stroke motor doesn't come with a cylinder head with a dedicated valve train to time the intake and exhaust charge, so they rely on other, less accurate, parts to time the intake and exhaust charge.

An important part of a newer two stroke motor is the exhaust (power) valve. The power valve helps the engine to deliver torque in lower RPM's (usually below 7K RPM) while maintaining high levels of power and a wide open throttle (WOT). This is done by sliding back and forth in a dedicated passage inside of a cylinder, which modifies the cylinder port timing. As you can guess, the sliding part is an important piece of this equation.

Two stroke motors burn oil and gas when they are running and as a result all power valves will have to be cleaned eventually. A general rule I follow is to check them every 1,000 miles. However, valves should be checked more often if they are not properly tuned, if they idle excessively or if the owner runs cheap two stroke oil.

When the motor runs dirty the power valve tends to get covered with carbon deposits and it impedes the valve's ability to slide. When this happens the valve will "stick" in one position and your sled will either lose low end torque or high end power.

To start you need to remove the power valve from the cylinder. I would make sure you have a set of gaskets that seal the exhaust valve to the cylinder - as I tear the gaskets 50% of the time when removing the valve.  Sometimes valves can be a little tough to get out, but if you give the valve itself a small spray with fogging oil and pull the valve by gently wiggling it back and forth they will eventually come free.

Magneto side power valve after 1200 miles. You can see the carbon deposits on the valve.

To start, hold the valve down and spray carburetor cleaner on the valve surface to remove any oil from the valve. If there is not much carbon on the valves you can also use a Scotchbrite pad. If there are a few chunks of carbon you can use a razor blade to remove the larger carbon deposits and then polish the valves with Scotchbrite. In extreme cases I've had to use a small wire wheel with soft bristles to remove the deposits from the valves. Most valves aren't made of a very tough metal so you will always want to work with caution so as not to scratch the valves.

Once you get the carbon off the valves you can polish them with a Scotchbrite pad.

Once the valves are cleaned you will also want to check that the they are operating correctly outside of the sled. Press the valve back into the valve assembly and then place your thumb over the hole in the valve cap. The valve should come out a bit and then hold its position. If it drops all the way out, the bellows will have a pinhole or rip in it and they will need to be replaced.

Check that the valves are working properly outside of the sled

Before putting the valve back into the sled you need to check that the passage from the cylinder to the bellows is not blocked. Turn your clutches so the piston is at bottom, dead center. Place a small airgun on the passage and try to blow air through it. If no air goes through, you'll need to poke a small piece of wire in through the passage to clear it.

Check that air can get from the cylinder to the exhaust valve. Be sure to test with the piston at bottom dead center or else the piston will be blocking this port.

Once this is done install the new gasket (if required) and then install the valve back into the cylinder with a small amount of thread locker on the bolts to ensure they won't come loose.

 


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