250-500cc Front Power Valve Cover Removal and Cleaning

Bike: 2000 WR250

I have run into an issue during the top end replacement. Currently the power valve is stuck in the open position. The cylinder was cleaned with easy off oven cleaner. I sprayed the left and right sides with carb cleaner.

I am now stuck trying to remove the front cover. The 4 bolts have been removed, but since this engine probably has not been disassembled for several years, the front cover will not budge.

My next option would be to use a torch to carefully heat the area in hopes to soften the material holding the cover to the cylinder. Does anyone have any other recommendations on how to free the cover.

Thanks in advance,

Eric

lightly tap it with the ruberised handle of a screwdriver, this will ensure you dont hit it too hard.
i assume the heads off the bike can you soak in in graffiti off overnight this will eat the carbon from around those power ports.
can you get the top cover off to expose the internal powervalve set up? if so then squirt carb cleaner down the holes to help free it all up.
be patient and dont hit it hard just tease it out.
good luck

dunk the whole jug in paint thinner and soak, then, carefuly score the gasket/parting line with a thin razor blade. rub some penetrant (kroil) or gasket remover in the joint. wait a while and gingerly work it all way round with a thin putty knife, little at a time like a paint can lid. add more penetrant as nec on any parts holding up the job and soak and wait. patientce is a virtue but it will come off. i dont like torches in these areas, turns oil to carbon and if there's anything remotely flamable that can catch, it will, and good luck putting it out then short of a bucket dunking. make sure you replace any plastic and rubber bits that get solvent and such on them.

Check the PV bearings too.

They are a PITA to change but they do go bad.

The whole PV setup on the 250/300 is a bid overly complex.

Make sure you use "clean" 2 Stroke oil for PV motors to cut down on carbon build up.

Try soaking it in a solvent like kerosene over night then try applying a bit of heat from a heat gun, this will negate the flammability issues with a torch and will soften the goo that is holding it all together. As juicy said give it a few taps with a rubber coated screwdriver or try a nylon faced hammer.it may need a few soakings so Take your time and it will come apart without damaging it.

Well, I was able to get the power valve cover off. Seems like there are many more issues I found. The power valve was missing an o-ring (caused the excessive oil in left hand PV cover), the bearings are toast, and the 2 side power valves seem to be sticking and causing issues with the smooth operation of the mechanism.

I would like to replace the 2 bearings in the side of the cylinder head that hold the circular power valves in place. Does anyone have any recommendation on how to remove these pieces. They are blind bearings with the gear in the center so I am not sure the best way to extract.

Eric

If I remember correctly, the gears have threaded holes (5mm?) that a slide hammer stud can be threaded into.

Thanks. That is what I found. I will look tonight and get the correct bolt for my slide hammer. I was also thinking about using a socket and 5mm bolt/all-thead to make a makeshift puller tool.

if you have trouble with blind bearings usually in crank cases, i shuv them in the oven @80 for half hour usually the bearings just drop out. i put the cases in the cold oven an let it warm up at a slow rate...

almost off topic but not quite.
any other tips???

Just wanted to provide an update and ask another question to those that have rebuilt the 2-Stroke power valve.

- Pulled bearings out. I found the correct bolt and built my own custom bearing puller. They were in really tight and I broke several bolts (highest grade I could find) in pulling it out.
- The roller bearings have been replaced with brass bushings (new husky part number).
- Found issue with head that there was a burr or slight out of round (not measurable) on the cylinder bearing surface. Took head to machine shop to ream each side.
- Bushing plus side power valve inserted and spin freely
- Replaced bearings on power valve shaft (old ones were very rough)

Each of the individual pieces (side valves and main power valve shaft) all move freely as individual components. When I assumable the system it does not move as smoothy as I would expect. When everything is assembled and I move the valve lever up and down by hand, the power valve just snaps open and closed, It is more of a jerky motion than a nice smooth opening. Is this jerky motionl due to the geometry of driving mechanism, or am I misting something in the assembly?

Also, when reassembly the front cover, I inserted all the o-rings for the water passages. Is there any additional gasket material (yam bond) recommended for the mating surfaces?

Thanks for all the help in this frustrating rebuild.

i just used the o rings its actually a really good design as max cooling around the hottest part of the cylinder.
the mechanism is it binding on oneside more than the other?
there are lock bars that if these are tight on the bearing case it caused notchy motion, like i think im reading from you.
the left side was the culpret,a tap with the handle of a screwdriver freed it up. also if you run the bike without those lock bars in the bearings were pushed out by the exhaust pressure.

Thanks for the reply.

I have the plates installed and the side valves rotate smoothly by hand before I assembly the power valve assembly. I can try to back the side plate bolts off a little to see if that is causing the increase in friction.

I guess my basic question is: Should the power valve assembly move smoothy when operated by hand? I can push up on the actuation lever and the spring has to fully compress and the pin contacts the power valve before it starts to open. Is this typical, or should the power valve be able to open under the force of the spring alone?

I will disassemble and see if I can identify which part is adding additional friction.

Eric

yes it should be smooth by fingers as there is a small plastic rod that will snap if the whole operation is tight.
just undo the 8mm bolts that hold one side on try it and then try the otherside.
the spring should smooth out the delivery of the mechanism but should move as you use the lever.
it should return on its own weight.
are your new bushes clean? a small amount of carbon or dirt from a thread can cause them to bind, also are they an exact size mathc of the originals as if they are over long this could be the problem right there.

good luck and no worries with reply