KX-500 Compression Release Mod! Easy Starting!!!

[Brett]

Why rebuild already, 200 miles is stuff all only 4 or 5 rides.  Did you check the ring gap of the old rings.  Thinking about it though the wiseco pistons are s**t and collapse readily.  You should also measure the piston with a mic as i bet it is now oval the wrong way.  Forged pistons of this size have no structural strength compared to a casting.  I was even squeesed my old one in a vice to put back into original shape but it was too late though cos i had allready baught a new piston.  Don't mean to bag ya but i just will not be convinced.  I have to admit though it is good to see the lining hasn't flaked at all, any chance of a photo of piston on side where release valve is?

[gowen]

Hmmm. Wiseco is my brand and has been for 15 years and no problems in every bike I've owned.

[Kawadougie]

You didn't read my previous post.    I've been running this piston and ring set for two years now.  I ran the compression release for about 200 miles with the old piston before a rebuild.  

[Torch654]

Did you realy put a smaller kicker on it? Evertone would think you were superman with a 125 kicker on it hehe.

[IridiumRed]

Thinking about it though the wiseco pistons are s**t and collapse readily.  You should also measure the piston with a mic as i bet it is now oval the wrong way.  Forged pistons of this size have no structural strength compared to a casting.  

Hey, this might be a big piston for a motorcycle, but remember, this would be a SMALL piston for a good sized american V8 (the small block chevy 350 was 4.00x3.48" Bore/stroke - about 100mm by 87mm, if i remember correctly!) And IF you have a motor that will be leaned on hard - raced, nitrous, lots of blower pressure, etc - you should run forged pistons

Its one thing to say that wiseco pistons are crap quality.  That may or may not be true, but I dont think you can say that a forged piston of this size has no strength.  That doesn't make sense to me.  There are forged pistons a lot bigger, they're tough as hell, and there are smaller forged pistons, also tough as hell........

Maybe i'm missing something, but i dont see what would make an 86mm dia forged piston weak - at least by design??

[gowen]

Ahh, I think he has forged and cast confused. Because I've shattered cast pistons before from age, but have NEVER NEVER EVER seen a Wiseco collapse or even come close. They do freeze easier without proper breakin or not letting them warm up. Iridium is correct, when my dad and I built the motor on my mustang we used Forged. Extremely strong and will withstand much more than s**tty cast pistons.

[Spider]

I find it hard to beleive that a company could stay in buisness as long as Wiseco has by selling a bad product.

2 cents worth
Dale

[Timbowe]

Wiseco have served me well. Been using thier product for 20 years. Faultless!

[Johnniespeed]

I have used Wiesco in every two stroke that I have ever took apart. I have never,  ever had a piston failure or siezure.  On another two stroke forum for non green bikes, they refer to Wiesco as "sieze-co" pistons. I guess some people have had problems, but  I am guessing it is due to piston to wall clearance and break in procedure. Forged pistons are stronger, but they expand greater than cast.
  While we are talking about pistons, how long do pistons last in the KX500? Do the skirts wear and cause the piston to get sloppy? Is the KX500 stock piston cast or forged?

[gowen]

Um to answere your question.. I had a "Wiseco" in my 500 for about 2 years of every weekend hard riding (except rain) and just had it freeze this past summer and that was my error (no 2 stroke oil during a drag race) . So I'm assuming a good  hard 400-500 hours is what I had in it? That would be 8 hour rides about every other weekend? And to be honest, I did not have any slop in the piston before locking it up. And the stock piston is cast.

[Rowdy-Yates]

Ive used Wiesco's in every bike I have owned!

[doordie]

I`m trying just now PROX in my MX-bike.
It`s lighter ,but don?t know how it last(only 4 hours on it)

//doordie

[Brett]

The issue with forged pistons of this diameter 86mm + is that when forging it is basically a big dick of one piece that gets pushed into the ally blank.  This method is perfectly fine and give great grain flow following the shape of the piston but being one piece has cannot give the webbing that a casting can.  A casting is often a five piece inner core that after being cast they get removed in a certain order.  due to this they can give very rigid design pistons with all the webs they have internally.  Forged pistons are perfect for 4 strokes due to pistons being very short and they have internal webbing as they don't have to seal of ports with the skirt.  Generally most racing 4 strokes have the gudgeon pin nearly touching the oil ring.  From many two stroke race engine builders i have spoken to they all choose pro-x pistons for the big capacity two strokes as they don't go out of round the wrong way.  Cast pistons being more rigid and often less ductile material which is more likey to shatter rather than oblong.  Cast pistons are also prone to shrinkage porosity in the heavy sections around the pin bosses.  You will get many hours out of a 500 piston due to the fact they put out stuff all specific power and also rev stuffall.  They reckon the hand grenade style racing 450 4 strokes these days have less piston life than a 250 twostroke as they are revving so hard and everything is on the limit to try and get as much power as a twostroke.

[Timbowe]

speaking of high reving 4 strokes, a dude from round here got shot of his CRF450 cause it stretched the valve stems! Not only once, 3 times!! A young chap I was talking to at the ride yesterday, said to me I,m saving up to buy one of those in a few years second hand. I told him there will be no running second hand ones worth buying...

[quincyman]

Here you go.  This is amazing.  The compression release works.  The mighty KX500 now starts as easy as a 125.  You pull the lever and it kicks through like nothing and usually starts first kick.  If you look at the photo, it is installed about an inch from the top of the cylinder.  It still has enough compression to fire.  I even put in the thinner head gasket.  Best money I've ever spent.  I was looking at buying a 250 but now I'm completely happy with my 500.  

Now that you have had this mod for a while, what do you think of it? Still no problems? I'm getting ready to make the plunge.