Maintenance & Technical > KX500 Original

Kx500 head gasket cooling ports

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reklessj:
Wrong gasket bro!!

Bcsnowbiker:
Well that's the gasket that was in there and that is what my new aftermarket tusk one looks like, exactly the same.
Holes and everything line up right but the water jacket holes are small

sandblaster:
There is a balance between too much flow and not enough.
There has been a lot of discussion on what is correct.
You will also note that the holes on one side is smaller than the other to force the coolant to cool the top end evenly :-o

I have thought some about changing the holes sizes but have never done it as I have always managed to keep my engine at a good operating temp.

If you experiment be sure to document what you do.

Bcsnowbiker:

--- Quote from: sandblaster on May 14, 2019, 11:16:32 AM ---There is a balance between too much flow and not enough.
There has been a lot of discussion on what is correct.
You will also note that the holes on one side is smaller than the other to force the coolant to cool the top end evenly :-o

I have thought some about changing the holes sizes but have never done it as I have always managed to keep my engine at a good operating temp.

If you experiment be sure to document what you do.

--- End quote ---

Thanks for the clarification on that 👍
I hadn't gotten around to noticing that the holes were a different size yet
Speaking of head gaskets I measured my squish today at 2.2 mm with the 1mm head gasket. The 0.2mm head gasket would put my squish in the right zone. Do you typically run this gasket? Thoughts on the raised compression?
I know compression is usually good for bottom end, I want top, but is better for altitude, which I have, but also adds heat, never a great thing.
Gas wise I use avgas so 100mon is achievable though I typically mix with 95. thanks

sandblaster:
Chuck that 1mm gasket and get a .2mm gasket.

Oh boy, I'm gonna start some controversy here  :-o
The number one thing to remember is trapped volume vs compression ratio.
In other words, how much air by volume are you compressing and how many times are you compressing it.
All other head design aspects are important but secondary to trapped volume vs compression ratio.
At sea level atmospheric pressure is 14.7 lb per sq in
At 5000 ft it drops to 12.2  lb per sq in
So lets say that you are compressing X volume at 13.7:1 compression ratio
At sea level that's 13.7 x 14.7 = 201.39 psi cylinder pressure.
At 5000 ft its 13.7 x 12.2 = 167.14 psi cylinder pressure.
The higher in altitude you go the lower your cylinder pressure is.
On a KX500 for good all around performance you want your cylinder pressure to be around 170-200 psi.
Unless your head, cylinder, or cases have been machined (and by your measurements they likely have not been) using the .2mm gasket is your wisest choice.
Otherwise you are lowering your compression over stock numbers as you are adding approx 1.5cc volume per .2mm gasket thickness... In other words you have raised the volume by a total of about 4.5cc greatly lowering your compression ratio. Then factor in the altitude and your gonna have a real lemon using a 1mm gasket...

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