shaggyzr2
Active member
I've had good luck with SPI pistons, they are cast pistons like the OEM's so you won't have to worry so much about cold seizures, they are also much cheaper than wisecos. You could go with SPI parts and have around $150 in it. Or you could do OEM pistons with aftermarket gaskets.
So the forged Wiseco pistons take longer to expand than the stock cast?
shaggyzr2
Active member
Forged expand quicker
A couple of bucks
VIP Member
Expansion rates are different between Wiscos & stock. Different material and different process.
I gotcha now, quicker would make sense for seizures since the cylinder wouldn't have enough time to expand properly yet until up to temp. Thanks
Martin Hall
New member
That's interesting ! So just to be clear if you do run wisco pistons you shouldn't have a problem as long as you let the sled warm up properly? Or is it that they expand so much faster then the cast aluminum cylinders that they will cold seize at idle ? I always let my triple sleds warm up for about 20 25 minutes. I check each cylinder with my hand and the pipe, to assure the engine tem is up. Then I check my heat exchangers, if they are not warm the sled don't move because that tells me the coolent in the block has not reached a high enough temperature for the thermostat to open. Then no hard acceleration for the first 5 miles just steady fluctuation of the throttle. The
Martin Hall
New member
That's interesting ! So just to be clear if you do run wisco pistons you shouldn't have a problem as long as you let the sled warm up properly? Or is it that they expand so much faster then the cast aluminum cylinders that they will cold seize at idle ? I always let my triple sleds warm up for about 20 25 minutes. I check each cylinder with my hand and the pipe, to assure the engine tem is up. Then I check my heat exchangers, if they are not warm the sled don't move because that tells me the coolent in the block has not reached a high enough temperature for the thermostat to open. Then no hard acceleration for the first 5 miles just steady fluctuation of the throttle. The
For a trail sled i like to go OEM pistons as they expand and contract more closely with the cylinder they are fitted to. I just like the piece of mind as it only takes once to seize a piston. If you do go with forged pistons be sure to measure accurately and use the different clearance spec for that type of piston. You will generally need a higher piston / cylinder clearance when using a forged piston.
Martin Hall
New member
Well I got it runing good agine there was water in the gas when I cleaned out the carbs . Piston kit is on its way though. Whent with spi pistons. I am getting a brand new Polaris switchback assault 800 next week end !! The Yamaha will be my girlfriends sled