Stainless steel power valves?

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#1
We were putting together the 240 the other night but had to wait to install the the top end because of ANOTHER broken power valve. It was the left side this time. (we must have missed it when we tore it down 4 months ago) Then we were remembering how many times we have had to replace the aluminum pieces on both bikes. It is getting very old.

To the point, my hubby said that he would like to make the aluminum power valve pieces out of stainless steel! He is an engineer at a very nicely equipped machine shop so it would not be a big deal. Is this a cool idea? I am tired of spending $30 a pop everytime I rebuild the top end.

Don't the KX500's use steel power valves? Why put aluminum on the KDX's? Am I the only one whos valves keep breaking? ... the nub in the bottom of the right and left sides and the gear teeth seemed to get chewed up. Any comment or suggestions?

Brenda
 

WoodsRider

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#2
Brenda - Unfortunately the '89 - '94 KDX power valves were more prone to breakage than the '95 - current KDX power valves (which are very similar to KX power valves). The problem with making them from stainless steel is a thermal one. As any material heats up, it expands. Aluminum has a different coefficient of thermal expansion than stainless steel, which may cause problems during operation. Since the aluminum valves tend to break when they become siezed, it is basically the weak point. If you strengthen this weak point, something else is going to break which may be more expensive to repair.
 

smb_racing

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#3
it appears to me that the valves don't break as much as they strip out. I'd lay down my good money for a quick fix, but ultimately you have to jet the bike cleanly to prevent carbon buildup. So far I'm doing alright with keeping my 240 cleaned out :)
 
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#4
On the last top end, I replaced the valves so they were clean to start with. When I took them out this time, there was no biuld up and they were quite clean, so i just think it is the material that is the weak link. My hubby does know that the two metals expand at different rates so he will compensate for that.

Woodsrider, you said they break when they become siezed. What would cause them to sieze, besides mass amounts of carbon build up?

Brenda
 

WoodsRider

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#5
Brenda - When looking to implement a material change to a component, you have to use the "fuse in an electrical circuit" analogy. The fuse in a circuit is designed to fail before other, more expensive, components are damaged. Anyone who has even a little knowledge of electricity knows that if you are blowing fuses you do not simply install a larger fuse.

In your case, you are saying the valve material, aluminum, is the weak link (fuse). If you fabricate new valves from stainless steel (a bigger fuse), will this create other problems within the assembly? To answer that question, you'll need to find out what is causing the valves to break. This may or may not be worth your time, but there has to be a reason why Kawasaki changed to the KX style power valve in '95.

Carbon build-up is the main reason for the power valves to seize.
 

Canadian Dave

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#6
Brenda being the head is still off the cylinder have a look at the holes the bottom of the sub port valves fit into. Over time they can become enlarged and sloppy. This sloppy fit can cause the values to become misalign and if its bad enough they will bind in the bore. There are a couple ways you can fix the problem. One is to take a punch and make indentations around the hole, normally at 4 points. This will cause the metal to deform some making the hole a little smaller. You then resize the hole with an appropriate size drill bit.

The second method is a more permanent fix. If you have access to some basic machining equipment and the know how you could install a bronze bushing for the valve to rotate in. If you really wanted to go hog wild perhaps even a small needle or roller bearing?

If your sub port valves were clean and in good condition yet still snapped or stripper this is likely the problem.

Polishing the valves will help prevent them from sticking. You might also consider having the valves hard anodized?

Hope that helps,

David
 
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#7
Thank you for all the great responss. Woodsrider, your analogy was great. I completely understand what you are saying.

Dave, I am hoping that the holes are the weak link. It seems to make sense because of the way they break. I already have the 240 bolted together so I will wait until the 200 needs a top end before I check it out. I also have a brand new, still sealed in oily plastic cylinder that I can use for measurements. I really like the bushing/bearing idea and will do that the next time around.

The polishing idea sounds like fun and all, but too much work for me. I already did the hard anodizing about 4 years ago and it didn't do squat. I thought for sure we had something there, at least longevity. NOPE!

Brenda
 
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#8
Woodsrider,

The KX500 has the same p.v. setup(different physical size) as the 89-94 KDX and uses steel or stainless powervalves so I don't really think it's designed to act as a "fuse". Aluminum rotating in aluminum is not a good thing no matter how you slice it. I really can't see any reason Kawi used aluminum parts.

Dave,

I have tried hard anodizing the parts but the results weren't impressive. The hard anodize adds thickness to the surface of the part and I didn't remove any material prior to having them plated. I like your bearing idea, may try that next time.