Maintenance & Technical > KX250 / KX125
BEWARE of Pro-x Pistons (pics)
Wayfast1500:
I was having problems with low compression in my 2000 kx250. It turned out my cylinder was out of round so I ordered a brand new OEM Kawasaki cylinder from a local bike shop.
Since owning the bike I put in a wiseco piston after getting the bike to freshen up the top end. The piston that came out was a pro-x piston, and the skirt had a big chunk missing. Since I didnt put the piston in I figured someone must have dropped it while doing the top end and broke the skirt since I never saw any signs of scoring on the cylinder walls.
After the new cylinder setting me back $500.00, I decided Id settle on the cheaper Pro-x piston instead of spending another $130 on the wiseco. I put the new top end together, the bike started first kick, I let it fully warm up and idle for a few minutes then I shut it down and let it fully cool off and repeated this process 3 or 4 times.
The bike sat for a few weeks while waiting for other parts, I finally got everything back together last night, and decided to go for a break in ride since I was getting out of work early. I started the bike today and let it warm up while I put my stuff on and secured the truck. I was taking it to a big field so there would be no need for high revving or putting a ton of load on it.
I took off, keeping the revs below/bottom of the powerband and shifted it in to second taking it easy. As soon as I hit second I heard a ping and the tire locked up. I knew it wasnt a heat seize so I put the bike back into the truck and headed home.
I pulled the top end off and saw a identical chunk of skirt (same size, shape and location) was taken out of the new piston. It looks like the skirts on the pro-x pistons are too long and slam into the crank when it expands from revving. This piston did not have a minute of riding time on it, I was only 20' from the truck when it happened.
Brand new cylinder, you can still see the hatch marks.
Wrist pin half in a pro-x piston and half in a wiseco showing the difference in skirt length.
Both Pro-x pistons out of the same bike side by side showing the damage to the skirt is identical.
New pro-x piston
New pro-x piston, the rings were seated correctly its hard to see the split around the dowels.
I will be contacting Pro-x, I am not sure what will come of this but dont buy this product as you can see from the pics it isnt coinsidence 2 seperate pistons made years apart failed at the same place
maddoggy:
i'm sure you are not the only kx500 running a pro-x piston. makes me wonder about your rod length. not defending pro-x but i would measure your rod compared to a new oem rod. i don't know your bike but you may find a difference(your rod being shorter) especially if you are still running the same rod it had in it when you bought the bike. just a thought.
Wayfast1500:
It has a hotrod rod, but it's a stock replacement, the piston travels to the top of the cylinder.
seff23:
i've been running pro-x pistons for a while and never had a problem
Dutch-K5 Fan:
Many things of Prox are oem parts or made by the oem manufacture.
If I were you I'll go to your dealer and ask if he has a stock oem piston to match with your prox.
If the prox is longer, than it's not wright.
Maybe there has been some modifying done with your engine you don't know about??
Here some people modid some RM125 in 99 or so with longer rods and used a TM125 piston.
the wrist pin was higer in the piston to compensate the rod. Could run with a stock at low rpm, when revving it
hit the sparkplug and stopt. Maybe somthing like this???
Dutch
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