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KIPS Advice - 04 KX250 Top End Rebuild

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I have removed all the KIPS parts and I have a few concerns that I think you more experienced members can help me out with. First, the main exhaust valve has some area on the bottom that is scratched. It looks pretty lousy but it really isn't very deep. Before I took it out I moved it in and out of the bore and it felt very smooth. Is this a big problem and should I replace this part? You can also see on the cylinder itself where the main exhaust valve was scraping. I don't know what caused this, but there wasn't anything in there and the KIPS wasn't bound up or anything. Maybe sand or something - I don't know. I am the second owner on this bike and I don't think it ever had a top end done. Here are a few pics of this. One is of the top of the valve and it looks much better.

KIPS04KX2501.jpg

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The subvalves look better, but on both of them there are two or three gear teeth that have shiny spots where it must have rubbed or been bound up a little. It could have been the same event the damaged the main valve that did this too. I know the aluminum subvalves are softer than the steel parts like the operating rods/racks so I suppose they will wear out earlier. There is nothing that I think would keep them from functioning fine for a long time to come with regular cleaning. These pics are of before cleaning of the subvalves and after cleaning all the parts. I used oven cleaner, but I left it on for no more than a minute or so and did a few applications. It really took off some stuff that I figured was never coming off, but I stopped where I thought the parts would be as good functionally as they could be. More oven cleaner and more time and they could all probably have no stains on them....

KIPS04KX2506.jpg

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Cost to replace the main valve is $90. The subvalves are $35.50 each. ~$160 thru TT but I am hoping I won't have to replace these.

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looks like carbon build up. im not sure bout the main, but the subvalves look fine. its not a precision fit like a piston/bore fit, but it should still fit well and slide smoothly

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I'm surprised at how KDX-like the 250 powervalves are! My '05 125 valves are nothing like that. Shows what I know, I guess.

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Looks fine to me also. Living in the exhaust port is a tuff life, lol. It will work better clean.

Ed

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Looks fine to me also. Living in the exhaust port is a tuff life, lol. It will work better clean.

Ed

I'm glad these parts look OK to re-use to you guys. I'll get the cylinder as clean as I can and put it back together with a new piston, rings, bearing, pin and gaskets and I do believe it will run like new. Have you all used any kind of gasket sealant with any of the top end gaskets before? I have a cometic top end set and it says you don't need to use anything except to grease the o-rings with something suitable. I had no leaks before, but it seems like the surfaces that seal at the cylinder base gasket are not even all machined. Some of it is machined and some of looks like it is just smooth cast surface. I figured it would all be machined to make a nice flat sealing surface. It has never leaked since I've owned it...I guess I should check the sealing surfaces with a straight edge if I can buy or borrow one.

It's kind of a bummer that 2 stroke development has slowed down so much, but with different materials maybe these parts could last longer and require less cleaning... I don't know what KTM has been doing or Husky or Yamaha for that matter (or Kawasaki in their non-USA markets), but why not make these valves out of titanium or something? Sure, the cost would go way up, but then lifetime might increase a lot too. You might be able to clean and reuse the same parts your whole life. Maybe you could plate the subvalve bores and the main exhaust valve bores with Nikasil too. I don't know...just thinking. I'm sure the thermal expansion coefficient has a lot to do with the choice of materials so nothing seizes, but that is something engineers could solve.

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