2006 RM125 Power Valve Rattle

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2/28/2018 11:45 AM

This has me stumped. I fully rebuilt my motor. Everything was extensively cleaned and prep'd. New crank, rod, seals, bearings, piston, etc. I put a forged CP piston in it since the factory one didn't hold up well to detonation at all. So initially I though it may be having a little piston slap which is normal for a forged piston till it warms up a little. I ran it for 2 heat cycles and it hasn't gotten any better or worse. With a stethoscope, the rattling is coming from the power valve. Using a borescope I inspected the piston and cylinder walls and they look great.

The only thing I can think of, the power valve was disgusting and covered in soot and slimey burnt oil. I cleaned the crap out of it and the ports. It was quiet beforehand. Now its loud. ? I'm also getting a bit of blow by out of the power valve breather tube. Which tells me exhaust is getting past the valve. Other than being dirty, it seemed to be in excellent shape.

I haven't gotten to ride it yet, hopefully Thursday or this weekend. I'm hoping it will just seal itself. Maybe at one point in time the metal was coated when it was new to help seal it?

Also, when I inspected the cylinder/liner earlier. I had the pipe off, looking up through the exhaust port, I pushed on the valve and it sprung right back into place. But prying on it up and down it does have some play within its bore.

Let me know what you guys think.

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2/28/2018 1:22 PM
Edited Date/Time: 2/28/2018 1:22 PM

Any idea which part of the powervalve it's coming from? Without sounding mad, put a handle of a T wrench to your ear and see if you can try and locate the noise by touching the cylinder while the bike is running. Only things it can be, off the top of my head:

- The retaining plate on the large central valve is held in place by two bolts. Perhaps these have worked out a bit and are allowing the retaining plate to vibrate against the cylinder
- Roller drums to each side of the central valve might be worn and vibrating. That guide and runner system doesn't wear very well. I smoothed mine out with a dremel and polished everything
- Linkage arm.

It's not the exhaust springs is it?

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2/28/2018 3:07 PM

I hear it more on the left side of the bike. But like I said, I can rock the center valve up and down with my finger, within its bore. Not very much. I need to ride it and see if it goes away under load. I did run a small 1" hone down the bore of the 2 side valves just enough to knock the carbon off and sprayed it out with brake cleaner. I cleaned all the valves, the center one had some wear towards the lower part of it. Looks like it had some kind of coating on it at one time but with heat and wear it's partially gone. The bolts for the center plate are tight. I used red loctite on them too and the center bolt. The linkage to the governor is tight and those bolts are loctite'd. I know nothing is loose, but I believe the valves are ratling around within their bores. I suspect it's the center one. For the bore on that, I just ran a wire wheel through it.

Maybe when I get home, just to identify that it's actually the power valve, I'll take the side plate off and rotate the power valve out and see of the noise stops. The front plate can't be taken off easily. Probably have to remove the motor mount bolts and rock the engine upwards.

The valves themselves are in excellent shape, I wonder if I can get them recoated in something to knock the vibration down if indeed that is the issue. New valves are stupid expensive. Looking at about $250

And no, not the exhaust springs. That would been way too easy. ?

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2/28/2018 3:19 PM

I recently rebuilt a 04 rm125 (same power valve design) and both of the side power valve inserts were worn where the pin goes. That grove opens and closes them so when it gets worn they will rattle and not operate correctly. Maybe look there.

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2/28/2018 4:08 PM

Hondas4Life3 wrote:

I recently rebuilt a 04 rm125 (same power valve design) and both of the side power valve inserts were worn where the pin goes. ...more

Those were nice and tight. And it operates smoothly. Im uploading a video right now for you guys. Definitely seems to be coming from the PV. When I open it, the noise quiets down. There is a touch of noise from the clutch hub bearing but you can't even hear it in the video.

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2/28/2018 4:09 PM

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2/28/2018 5:52 PM

If I were to get the front cover off, y'all think it would be fine to start the bike with the power valve removed to just completely rule it out?

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2/28/2018 11:00 PM

The breather tube is supposed to smoke a bit, that's why it's there. Also. The powervalves need oil from the premix

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3/1/2018 6:47 AM

Bruce372 wrote:

The breather tube is supposed to smoke a bit, that's why it's there. Also. The powervalves need oil from the premix

They're well oil'd by now, and I oil'd them during installation. I planned on riding it today, but it's freaking raining. I think I may just be a little paranoid.

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3/1/2018 8:55 AM

triple5moto wrote:

If I were to get the front cover off, y'all think it would be fine to start the bike with the power valve removed to just ...more

Yeah, you could run the bike for a bit with the power valve cover off, I've done worse smile.

The noise sounds heavy and deep to me, heavier than a light power valve part. Did you check the piston/cylinder clearance with a dial bore gauge? What crank did you put in? Was it in alignment and well balanced? Did you replace the main bearings? Any chance that they're not sitting perfectly true in their bore?

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3/1/2018 4:55 PM

It was a pain but i was able to pull the power valve with the motor still in the bike. There was wear at the end of both side valves like they were rattling. I think when I oiled them, there was oil inside the valve itself pushing the valve down even further. That's all I can come up with. I put them back in dry. There's still a rattle, but now when its idling I can play with the throttle and get it to go away. And as it was running the rattling was getting more faint. I suspect as they were getting lubricated again. Piston and cylinder still look fantastic. And there's no noise in the bottom end. I did a compression test last night and got 176 psi, 3 times. And the bike was cold.

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