cr250 Power Valves

[the nitro man]

i'm rebuilding the top end of my 89 cr250 with a new sleeve & piston, & the machine shop that did the work took the power valves out to keep metal from getting traped insine. i put the power valves back in & they seem to be right, but what makes them open & close? their not spring loaded to close them, so what closes them? i figure exhause pressure open them, but not sure. how can i tell if their installed right? thanks

[terboed]

im not too familiar with the 89 but my 97 was from a gyro kind of a deal where at a certen rpm it would start expanding and push on a lever on the clutch side right behind the water pump. the lever was attached to a rod witch went up and connected to another lever in the cylinder block. and a series of more levers untill it turned the pv. mine and your motor are prolly different though. so this will do you no good. alot of the newer bike are servo actuated pv's and the ecu controls when it opens depending on rpm and throttle position via a tps sensor. these electronic pv's help out a great deal when it comes to making consistent power.

[fiveOnick]

I believe its the same type of setup, I have not looked in the lower end of an 89 CR but have assembled the PV's. They are controlled by that small lever on the cases, which most likely is turned by the rotation of the crank through the small amount of friction on bearings. At a certain rpm enough friction is exerted to turn the valve and pull open the PV's.