Exhaust Valve Operation

gunslinger45 · Mar 10, 2004

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 · Mar 10, 2004

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 · Mar 10, 2004

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 · Mar 11, 2004

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.

Exhaust Valve Operation

gunslinger45

joelyles2004

gunslinger45

darringer

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