KX 125 going big!!

[RAH RAH]

Hey guys hows it goin?? I'm getting ready to rebuild a buddys' kx 125. He wants to go with a big bore kit and stroke it as well. What Im looking for are some good RELIABLE reports just so I can do the right thing and not have a stroker motor needing constant attention. Im not aware of what kits that are out there but I do know of some hot rod kits. He wants to buy the whole crank and rod assymbly as well as the piston kit. Are there any complete kits out there as in rod and crank or do they have to be assy. I dont really want to start a flame board here but what is the best size to bring a 125 up to. Ive seen plenty of bad results from what I believe is a 154 but not real sure.
Isnt there a trade off somewhere between the 150's and the 125's It seems that I had heard of it being like a 139 or something. Then again, thanks for the right help and the good and bad reports. :cool:

 

[CagivaWMX]

A 144 is the cheapest big bore kit upgrade. The myth of the 139 is that it makes more power than a 144. The fact is that was started by Rick Petersen and Max Power. The only thing a 139 makes over a 144 is more profit for Max Power. The 144 pistons are affordable and a catalog part through Wiseco. Max Power's 139 piston is over $200 and you can only buy it them. The Wiseco equivalent to the 144 piston sold by Eric is 846MO5800 and you can buy them from any Wiseco or Parts Unlimited dealer.

 

[RAH RAH]

thanks man, I definitely understand the marketability of those magazines.... I just want what works without all of the hype. It would be good if I just sent the 125 to eric and get back a 144. then again, I need to have the bottom end bearings checked by someone that knows. I might have a stroker kit on my hands. I havent checked them to see if there was any play or not. I was just told that they need to be replaced by the owner speculating. He might then still be more happy with a 144 rather than going even bigger.

 

[chrislaw1968]

A 144 is the cheapest big bore kit upgrade. The myth of the 139 is that it makes more power than a 144. The fact is that was started by Rick Petersen and Max Power. The only thing a 139 makes over a 144 is more profit for Max Power. The 144 pistons are affordable and a catalog part through Wiseco. Max Power's 139 piston is over $200 and you can only buy it them. The Wiseco equivalent to the 144 piston sold by Eric is 846MO5800 and you can buy them from any Wiseco or Parts Unlimited dealer.

the piston that came with my kit is a 836mo5800

 

[Eric Gorr]

There are 3 different types of 144 pistons made by Wiseco.
The 9816MO5801 is my custom piston that has been refined several times since 1991
the Wiseco catalog parts 846MO5800 and 836MO5800 are for the YZ and KTM/RM respectively. The YZ144 846 piston is the closest copy of my 9816 and interchanges. The 836 has a timing height 1mm greater, is flat-topped, and the cam shape is designed for triple exhaust port designs, whereas my piston is for delta shaped exhaust ports. We've used my piston in the RM and KTM before Wiseco made the 836 and didn't have any problems. But Wiseco has a special shape for the triple exhausts. Once a cylinder is set-up for one or the other piston, you can't interchange them because of the difference in the timing height.