Exhaust Valve Operation

[gunslinger45]

I've got my engine apart (top end) and when I observe the exhaust valves I don't see them move when I turn the crank. I would think that the rod that comes up from the crank case would be operated when the engine is turning, but I'm not seeing this. The valves work fine when I operate them by hand. Any thoughts? The bike is a 1988 RM 250.

Thanks in advance.

Trevor

 

[joelyles2004]

The rod does actuate the poervalve, but it works off vacuum (Rpm's) when the motor is up to speed. I was currently looking at the same thing yesterday on my top end. Wondering why the powervalve rod would make the valve move. I have a 1997 RM250.
The end of the rod that goes into the bottom end just free-moves on a shaft

Joe Lyles

 

[gunslinger45]

Thanks Joe, I hadn't thought of that. Speaking of vacuum, I have a follow on question. On this bike that I picked up, there seems to be a spot for a tube or hose on the left side of the engine, actually on the left side of the exhaust valve assembly. Any idea if there should a tube running from this spot to somewhere else? Is it just a vent port? I also have a similar fitting on the crankcase without a tube, but I assume that one is the crankcase vent, right?

Thanks,

Trevor

 

[darringer]

Actually, the bottom of the shaft is connected to a ball-and-ramp type governor. The faster the rpm, the more the balls move outward by centrifugal force, moving the powervalve rod. You are correct that it is a vent for the powervalve on the left side of the assy. It runs to the bottom of the motor and vents to the atmosphere.