How to clean and prep your KX500 exhaust valves

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How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Tue Apr 10, 2018 3:11 pm

Some have asked my how I polish up my kx500 exhaust valves.
So I did one last night as a demonstration and took pics.
Probably one of my biggest things I have to share is not to remove any more material then you have to.
The center flapper is cast steel and has little pin holes and is generally very rough...
The first thing to do is remove the pins.
You can see from this pic that the ends are very worn.
Remember, for ever .001" of wear you loose .002" of lift.
It is not uncommon to see these worn .020" or more :shock:
.020" of lift will reduce your port timing probably about 2 degrees and create that annoying KIPS rattle which in turn is creating turbulence from the flapper dancing around. Yes, you are loosing HP if you hear that KIPS rattle.


KX GURU RACING KX500 EXHAUST CENTER FLAP 101.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 101.jpg (427.76 KiB) Viewed 337 times
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Re: How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Tue Apr 10, 2018 3:12 pm

The first thing I do is give the center valve a quick run on the wire wheel to knock some of the carbon and gunk off so I can see what I am working with.


KX GURU RACING KX500 EXHAUST CENTER FLAP 102.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 102.jpg (191.19 KiB) Viewed 336 times

That's better...
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Re: How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Thu Apr 12, 2018 4:11 am

Next, it's time to remove those worn out pins.
So I use a Slidegrip, Map Gas, and a vice.

Before you pull the pins out, measure them and record it.
I like to make mine about 1mm or .040" longer then stock per side.


KX GURU RACING KX500 EXHAUST CENTER FLAP 103.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 103.jpg (873.64 KiB) Viewed 332 times


Then, I heat the valve on the thin side of the pin...


KX GURU RACING KX500 EXHAUST CENTER FLAP 104.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 104.jpg (257.6 KiB) Viewed 332 times


Once the valve is hot enough, about 15 seconds, I hook up the Slidegrips and give it a couple of quick slide of the hammer and it pops right out.


KX GURU RACING KX500 EXHAUST CENTER FLAP 105.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 105.jpg (601.05 KiB) Viewed 332 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 106.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 106.jpg (222.02 KiB) Viewed 332 times
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Re: How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Thu Apr 12, 2018 4:13 am

There are some guys that will pull the pins out and put the worn end into the valve, or while the valve is hot, twist it 90 degrees.
And that's ok, I just like to replace mine.
I use 4mm drill rod.
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Re: How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Thu Apr 12, 2018 4:19 am

Pins out...


KX GURU RACING KX500 EXHAUST CENTER FLAP 107.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 107.jpg (275.58 KiB) Viewed 329 times


A little more on the wire wheel and were ready to get down to some pre polishing.


KX GURU RACING KX500 EXHAUST CENTER FLAP 108.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 108.jpg (304.85 KiB) Viewed 329 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 109.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 109.jpg (216.69 KiB) Viewed 329 times


Because the center valve is cast steel it is very rough.
So I use a hand grinder with a fine flap wheel on it.
Remember... You only need to take of a skim... just break that rough surface texture off.
Don't worry if there are some pits and casting flaws... It won't matter...

KX GURU RACING KX500 EXHAUST CENTER FLAP 110.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 110.jpg (329.47 KiB) Viewed 329 times
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Re: How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Thu Apr 12, 2018 4:21 am

As you can see, it looks rough but it's not really that bad :lol:


KX GURU RACING KX500 EXHAUST CENTER FLAP 111.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 111.jpg (309.44 KiB) Viewed 328 times


After I get the two surfaces cleaned up, I switch to another flapper wheel which is made from a Scotch-Brite type material.


KX GURU RACING KX500 EXHAUST CENTER FLAP 112.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 112.jpg (290.08 KiB) Viewed 328 times


After the flapper wheels are done I run it on a bench grinder or polisher with a cloth wheel.
I use some green polishing rouge.


KX GURU RACING KX500 EXHAUST CENTER FLAP 113.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 113.jpg (762.35 KiB) Viewed 328 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 114.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 114.jpg (230.75 KiB) Viewed 323 times


So, the more time you spend, the better and smother it will look.
It took me about 20 minutes for the disassembly and polish.
10 more minutes of time would have been crazy 8-)
Just go easy with the grinders, less is more.
If bikes are for kids I'll never grow up.

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Re: How to clean and prep your KX500 exhaust valves

Post by Sandblaster » Thu Apr 12, 2018 5:22 pm

Here is about 5 minutes more on the polisher..


KX GURU RACING KX500 EXHAUST CENTER FLAP 117.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 117.jpg (300.58 KiB) Viewed 285 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 118.jpg
KX GURU RACING KX500 EXHAUST CENTER FLAP 118.jpg (297.89 KiB) Viewed 285 times


As you can see, you get diminishing results.
Sure, it is better and I could get it better yet but for me it's plenty good enough for what it does :lol:
Next up is the drum valves.
If bikes are for kids I'll never grow up.

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