How to clean and prep your KX500 exhaust valves

[Sandblaster]

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
.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 (427.76 KiB) Viewed 13401 times

[Sandblaster]

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 (191.19 KiB) Viewed 13400 times

That's better...

[Sandblaster]

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 (873.64 KiB) Viewed 13396 times

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

KX GURU RACING KX500 EXHAUST CENTER FLAP 104.jpg (257.6 KiB) Viewed 13396 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 (601.05 KiB) Viewed 13396 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 106.jpg (222.02 KiB) Viewed 13396 times

[Sandblaster]

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.

[Sandblaster]

Pins out...

KX GURU RACING KX500 EXHAUST CENTER FLAP 107.jpg (275.58 KiB) Viewed 13393 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 (304.85 KiB) Viewed 13393 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 109.jpg (216.69 KiB) Viewed 13393 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 (329.47 KiB) Viewed 13393 times

[Sandblaster]

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

KX GURU RACING KX500 EXHAUST CENTER FLAP 111.jpg (309.44 KiB) Viewed 13392 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 (290.08 KiB) Viewed 13392 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 (762.35 KiB) Viewed 13392 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 114.jpg (230.75 KiB) Viewed 13387 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
Just go easy with the grinders, less is more.

[Sandblaster]

Here is about 5 minutes more on the polisher..

KX GURU RACING KX500 EXHAUST CENTER FLAP 117.jpg (300.58 KiB) Viewed 13349 times

KX GURU RACING KX500 EXHAUST CENTER FLAP 118.jpg (297.89 KiB) Viewed 13349 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
Next up is the drum valves.