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

[don46]

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.

MD, he's running a KX 250, defineately looks longer than the wiesco. for me I'm not a fan of cast pistons, forged only, let the debate begin.

[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.

MD, he's running a KX 250, defineately looks longer than the wiesco. for me I'm not a fan of cast pistons, forged only, let the debate begin.

ya i noticed the 250 thing but not until after i already posted it. i would agree on the forged piston. forged is almost always stronger than cast in any metal in any application. i still wonder about rod length though. it sure took a large chunk off.

[don46]

[/quote]

ya i noticed the 250 thing but not until after i already posted it. i would agree on the forged piston. forged is almost always stronger than cast in any metal in any application. i still wonder about rod length though. it sure took a large chunk off.
[/quote]

I would say no issues with the Rod, look at the picture with the wrist pin in the Pro x and Wiseco it looks like its at least .080 to .100 longer than the wiesco which would explain why its breaking as it expands .

[Wayfast1500]

It is a hot rods rod, stock specs it isnt a stroker rod or anything.  When I had the wiseco I had high compression base and head gaskets and if the rod was too long it should have hit the head.  Rod bearings are tight, no vibrations or sounds indicating bad crank bearings or a out of balance/out of true crank.  Ive had this bike to the limiter with the wiseco which was the piston in there right before I did all this work.

[kwakman]

it sucks that you spend a chunk of hard earned to get it running right and just end up with more problems.there was a video on youtube where a bloke had checked a brand new wiseco crank and found it to be a mile off what it should have been;to cut a long story short, it transpires that wiseco rotating assemblies (not pistons) are being made in china or taiwan or sumthin.pro x are supposedly made by oem manafacturers.if I were you I'd get onto them and throw the rattle out of the pram, but unfortunately that wont help your cylinder.Just because its a relatively rare occurence doesnt mean they should get away with it.

[Roostmad1]

i agree that it really sucks when this sort of thing happens,i feel for you mate,stay away from pro-x is most probably made in china crap now like most things,what i do now if its not made in new zealand,aussie,US or germany or japan that part will not be going in or on my bike period,i,ve had it with this chinese rubbish,it because they can get a chinese "unskilled worker for a bowl a rice a day!!

[1989kawasaki]

if that happened to my fully rebuilt 89 kx250 with a fresh replated cylinder and wiseco piston, i wouldnt know what to do / say.

[jonny500]

there is nothing wrong with prox pistons, i have used them for 20 years with  no problems. there are 2 main manufacturers of piston is japan the art factory and the prox factory. both suply the 4 jap oem parts. you will see on genuine pistons that the name , on some is cast inside. there is some thing adrift here. either you have the wrong piston/year of bike or your engine geometry has been changed. 87-89 , 90-91 and 92-04 are the different pistons for the kx 250. if some of the other members that have old piston laying round could measure there pistons we may find  a difference.

[jonny500]

also is the crank true. i noticed it only has damage from 1 crank half. if the crank is badly out of true it would cause the crank half to have a high spot. i quick test woud be to turn the crank while looking at the gap between the outer diamter of the crank halfs and the casings on each side to see if the gap has much variaton through out a revolution

[BDI]

It may have nothing to do to with the length. The piston may be to big for the hole and if you ordered the new pro-x piston based off the number on the top of the old pro-x piston that would explain the identical damage. It is my experiance that when a piston is to tight the bike will idle just fine but when you try to ride it the piston sticks as soon as you try to get into the upper rpm.