Posts
14
Joined
12/30/2016
Location
Travis Afb, CA
US
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.
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.
- 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?
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. ?
The Shop
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?
Post a reply to: 2006 RM125 Power Valve Rattle