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Power Valve - Look Normal to you?

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Pulled the motor on my 2005 YZ250. Did pressure test, which was perfect. Replaced the generator, etc.

Today I inspected the Power Valve. Knucklehead that owned it before me must have used red Loctite on the screws. Twisted the head off one off before I realized nothing was turning. Thank you heat gun. Took a couple minutes at 1200 degrees and a hammer tap to loosen the screws. Used an Alden extractor on the twisted off screw. Those things have saved me many times now. Excellent investment.

So, the reason for the post is my inspection of the power valve. When I moved it, it took a little tap to get the middle valve to pop out. I would guess if the bike was running this would have happened immediately. After it first popped out it moved freely. My big question is, does the linkage look normal in the closed position? Anything you see I should worry about? How about my piston, pretty great for 20 hours I would say.

Is this closed all the way? I don't think so based on the manual photo of how to install the "set pin". Looks like the fork below the bolt needs to be aligned with the hole behind it. See next illustration from the manual.

598246f8233db_YZ250PowerValveClosed.thumb.jpg.62384c92a6f06c4605a68100bcf24186.jpg Set-Pin-Installation.gif.c22b89e6bf1ffa69d14429ff91f6025d.gif

Here it is open. I think this is fine.

598246f95c3d5_YZ250PowerValveOpen.thumb.jpg.69763a0d0cb58b92ff2607eb97f61b4f.jpg

 

See any issues?

598246f6de7ad_YZ250PowerValveAssembly.jpg.a746223c40a619712224675d0cdac0c9.jpg

 

Piston couldn't have looked much better after 20 hours.

598246f5a4af0_Piston15hours.jpg.db339c61506d598eb5019b42a1fc870e.jpg

Edited by LSHD

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Picture 1 is not closed all the way. The fork opening on the top arm needs to be directly in line with the hole provided on the cylinder. That's where the dowel goes in to hold everything for removal and install.
Picture 2 does not look open all the way, top arm travels almost too but not contacting the cylinder casting at the top.
Picture 3 is very dry. Is that how it was when you remove the cover? That picture is not showing secondaries all the way open

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Thanks Klinger!

That is what I thought. This probably explains the off-idle burble I've been getting. I'll take it apart and clean it up. My guess is carbon buildup from years of neglect.

I took the photo after cleaning with carb cleaner. Of course will lube after I disassemble to find out why it's sticking. I think the frozen power valve cover screws kept the former owner from ever opening it up.

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Nice find.  If all three valves don't fully shut then it could cause any odd issues you have at low RPMs. And if they don't open in the normal staged way, then you could have problems with inconsistent power at higher RPMs.

Could be gunked up.

Also common is for the side valve pulley-guides to bind a little on the pins - which can be fixed by loosening the set screws and re-positioning each pulley until the whole thing glides smoothly (with a little oil to help it).

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11 hours ago, Kinger317 said:

That's weird, was original post edited with manual pictures added?

Yes. I added them a few seconds after your post. Was actually editing while you must have been posting.

Edited by LSHD

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Found some carbon along the tips/ends of the power valve itself and on the two side valves. 

 

QUESTION: The power valve had some light scratching through the anodizing. At $150, I don't plan on replacing it. I sanded with 600 wet/dry and polished with Scotch Brite. Okay to do this? I'll get a photo tomorrow.

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Sounds reasonable to me. Check it each year going forward for slop/play. That is hard anodizing on the surface for better wear protection. The aluminum core is softer so if you sand down into the core it will wear quicker.
I'm surprised there was carbon buildup and wear, what year bike is this and what do you run for mix ratio? Generally speaking is your jetting on the lean side?

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2005. :lol:

 

I run 32:1. There was just a little carbon on the "horns" of the power valve, about 1/8" on the outside edges. More significant was this scratching on the bottom of the PV on the cylinder end. Again, I'll get us a photo tomorrow and see what you think. I think if I check it annually I can catch it before anything bad happens due to wear.

EDIT: Carbon went about 1/8" up the sides of the PV horns, not 1/8" thick!

Yes, normally my jetting is a bit lean.

Edited by LSHD
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Here it is. Looks like a chunk of something gouged it. Could have happened a long time ago. Top end has about 20 hours on it. In the photo you can see I sanded it "smooth" with 600 grit and Scotch Brite.

20170804_110525.jpg.cd7e046effc3cf6b308a01b70e45f17f.jpg

20170804_110515.jpg

Edited by LSHD

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Just make sure that whatever "chunk of something" that scratched it isn't still stuck in the cylinder.

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Inspected it today. Could not see anything at all, not even carbon. I'm going to brush it a little bit with plastic Scotch Brite just to be sure.

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UPDATE - After lots of inspection and dicking around for hours I can't get the exhaust valve to not stick. Best I can tell, and based on visible hone marks inside the exhaust power valve chamber, somebody got a little crazy with the hone and widened the chamber too much. This allows the power valve to sit at an upward angle (rear end low) when pushed in and stick tight.  Doesn't take much thumb pressure to make it stick so tight the PV springs won't pull it out. Maybe when the engine is running the vibration will pop it loose, but I don't know.

OPTIONS - Don't know if Millennium or Powerseal can fix this or not. I am really tempted to just replace the cylinder and top end, since I don't want to mess with this again and I have more money than time.

Any suggestions?

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When I had my cylinder plated, they went a little crazy and plated into the PV bore.  So much so I couldn't get the valve in the last bit.  Had to get handsy with a rat tail file (dirty method, I know) and marked/filed the high spots till it fit smoothly enough to not stick.  Now that it's had some cycles on it they've worn together some and moves very freely.  Not perfect, but like you, i'm not going to spend $150 for a valve and $400 for a new cylinder, just to that they'll work 'properly'.  They function just fine as is, scuffs and all.

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Well, not like me. Because I bought a new cylinder. Old power valve is fine.

Sounds like a good decision

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Thanks Klinger. Appreciate all your support and feedback on this weird issue. Wouldn't have guessed PV originally, but the bike is 12 years old.

I'm a mechanical engineer and can't stand for something mechanical to not work right. Will feel much better when this is done right and I don't have to think about it. Rocky Mountain had some good prices going, so I picked up a new chain, Ironman sprocket, etc. In the meantime my 4 stroke (KX250F) is finally getting some ride time. :ride:

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On 13/08/2017 at 0:32 AM, LSHD said:

This allows the power valve to sit at an upward angle (rear end low) when pushed in and stick tight.

Hmm, weird one. Was everything coated in oil while you tested?  Did you try to exploit any movement in the plate the guides the PV centre rod piece?

On 03/08/2017 at 7:42 AM, LSHD said:

Knucklehead that owned it before me must have used red Loctite on the screws. Twisted the head off one off before I realized nothing was turning. Thank you heat gun. Took a couple minutes at 1200 degrees and a hammer tap to loosen the screws. Used an Alden extractor on the twisted off screw. Those things have saved me many times now. Excellent investment.

Amazing you got that screw out! Would have beaten me!

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12 minutes ago, numroe said:

Hmm, weird one. Was everything coated in oil while you tested?  Did you try to exploit any movement in the plate the guides the PV centre rod piece?

Amazing you got that screw out! Would have beaten me!

Installed just the exhaust PV and valve holder. With and without oil, a mild press in and the PV stuck. Added the valve shaft and spring to see if spring pressure would pull out the PV. Nope. Stuck like cluck. I could use two thumbs to pull it out. Pull, pull, pull...POP! Sticky as heck, even though plenty of play. I am happy to believe it is too much play and will enjoy the new cylinder, knowing this thing is now correct. May goof around with the old cylinder and see if I can get a better fit if I get bored. But ready to move on from this vexing problem.

 

EDIT: Valve would always stick if I push up and back or straight in and back. If I pushed down and back (tipping up the rear end of the valve), would seldom stick. That is what makes me think (plus the gouge marks) that somebody just took off a bit too much in the PV chamber.

 

Seriously, the Alden extractors work fantastic. If the recommended size doesn't work, go up to a size just under bolt diameter. Even if bolt comes out in segments, still works. Heat gun and some hard taps with a mallet are essential.

Edited by LSHD
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