97 RMX250 power valve

Hi, can anybody tell me if I can remove and clean the power valve on my 97 RMX without removing the motor/jug.


Perhaps, but it would way more trouble than it's worth.


I don't think you could get enough downward pressure on the philips screws to keep from striping the tops. Then you would be pulling the cylinder anyways, and... have stripped out screws to deal with and replace too...


You could keep the head on the cylinder and pull both together to save yourself a head gasket if moneys a problem. Then you just need P.V. and base gasket, new ring(s), and I'd suggest a new plastic clip for the PV pushrod and o-ring for exhaust.

Good advice. Thank you.

As Jeremy mentions it is far easier to do the work with the cylinder removed, and I'll add those cross headed screws are pretty soft and susceptible to damage. Make sure to use the correct cross headed bit as there are philips and pozi drive types that do not properly fit if used on the wrong type of screw.


I prefer to loosen and tighten the screws with a quarter drive ratchet and correct driver bit as it is important they are tightened properly to ensure the guides are held properly.

If these screws are not properly tightened to clamp the guides the various PV blades and guides will be able to move and wear quickly with the force of the exhaust pulses hammering them every time the engine fires.


I managed to source high tensile screws to replace the standard screws, and a good wide washers to help clamp the guides.


And to finish, I can't stress enough how important it is for folks to check and maintain their RMX PV system as it can cause extensive damage if it is neglected to the point the guides or blades fail.

Thanks Dan. Any idea where I can find the cross head bits for these "Japanese phillips heads"

Found them. JIS- Japanese Industrial Standard.

Will be ordering a set.

I guess this is why all of my bikes end up with a stripped head on the air box/ carburetor intake boot clamp!!

Got my parts to freshen the top end. Took it apart to clean the powervalve. I found that the the guide set is failing. Each has a hairline crack at the thin part where the spring fits in the hole.

These things are expensive! Does anybody know of a secret place to get them cheap!?

The best price I have found is $230.00 usd.


The springs wearing through the guides is quite common. There is very little wall thickness in the area where the spring bore is. That said the design of the guide does mean both ends of the guide are still supported, so as long as the guide is not really badly worn it may well still be ok to use. New springs are pretty cheap so worth replacing them if they are showing signs of wear on the sides.


Was there any wear on the guides where they are clamped into the cylinder? The two guides need to be clamped firmly by the locating screws or they will rattle around and wear badly. Once that happens it becomes difficult to clamp the guides properly.


The mid plates are the real issue in the RMX PV system. The age of your bike suggests it should have the mid-plates with the small allen head and castellated nut through the plate. Earlier design just had a pin. Both designs suffer from the pin loosening off and starting to eat a slot in the plate to the point the plates drop far enough into the exhaust port that they catch the piston, which spells disaster...

Thanks for the reply.

That's good news if I can stull use them. The bike is my back up so it doesn't see a lot of use. Only has 2300 original miles so its a bummer that the spring holes are wearing through at this point.

They seem to be in good shape where they seat.

I will check the wear in the slots after they are fully cleaned and report back.

Here is a picture of the hairline crack in the valve.

I have checked for wear in the groove. Everything looks fine, and the guide screws have not loosened.

I wanted to check to make sure the powervalve control arm was not unhooked from the bottom end while I have the jug off, so I rotated the crank with the connecting rod. The control arm does not move, but it is not unhooked because I cannot remove it.

Does this arm only move at a certain rpm???

Please advise.

Thank you


I've stripped engines that had PV guides with significantly worse wear and cracking than the one in your pic. Reckon you will be fine running that guide for a good while yet.

Were the pins in the mid-plates tight and secure?


The PV system uses a governor to lift the rod that opens the valves. The engine needs to be revving quite high for the centrifugal force to be high enough to overcome the force of the PV return spring. You will not be able to turn the engine over by hand anywhere near fast enough for the governor to operate.

Edited by rmxdan

Decent. I was just worried about it chipping and getting into the cylinder. I am going to run them and check them over the next time I freshen up the top end.

Yes, the mid plate screws are good and tight. They also cleaned up nice.

All new screws and springs.

Thinner head gasket.

Almost back together.

By the way, picked up a set of Vessel JIS screwdrivers. Very nice.

Hey RMXDAN, you got time for a few questions about my '97 RM125? I just bought, and it runs but it's a beater.

First off, what is the function of the powervalve? Does it restrict flow out of the exhaust for more low-end?

Second question. My right radiator is all bent up. It doesn't leak, but I'd like to get it repaired or get a good one. Every schematic I've looked at makes it look like the radiator cap is on the right radiator. But on mine, it's on LEFT radiator. The outlets are pointed so that you've got to mount them this way. I've been looking on e-Bay for a good used radiator, and all of 'em have the cap on the right radiator, so it doesn't look like they would work for mine.....


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now