Pro X vs Wiseco for CR125

Hi, I am debating whether to put a Pro x piston or a Wiseco in my CR125. Im building it to sell it to a friend who is gonna learn how to ride on it. Not beat the shit out of it or MX it, ride up and down our state park and learn the feel of the bike. I was thinking more towards Pro X because he dosen't know much about the right warming procedure and such, and its a little bit cheaper and its a cast piston. Any input? What would you use and why?

Also, If i put a Forged piston in it, since i bought a reconditioned but lightly used cylinder off of a mechanic I know very well, whats the process with measuring the cylinder gap? 

Always use OEM or Pro x when you can period.  Wiseco will work but I don't trust them after I lost 3 engine in 2004 over there crappy stuff.

Also, If i put a Forged piston in it, since i bought a reconditioned but lightly used cylinder off of a mechanic I know very well, whats the process with measuring the cylinder gap?

You will need a 2-3" outside micrometer and either a set of telescoping snap gauges or a dial bore gauge. Dial bore gauges are not cheap but are 10 times easier to use than the snap gauges. If you are skilled enough to get accurate readings off the snap gauge it is a much cheaper solution. You will want to measure the piston 90 degrees from the wrist pin about 10mm off the bottom of the skirt. This is where the piston will be largest. Measure a couple times to make sure you are getting an accurate number.

Now using your snap gauge or dial bore gauge measure top, bottom, and middle of the cylinder in at least two places (90 degrees apart works). Not only do you want to know the size of the bore but you also want to know if it is out of round or out of taper. I'm not sure the specs for out of round and out of taper on the cylinder but they are in the manual.

Once you have accurate measurements of the bore and the piston simply take the bore measurement and subtract the piston measurement. What's left is the piston to cylinder wall clearance. Wiseco recommends a minimum of .0015". All said and done my Eric Gorr engine came back with .0028" which Wiseco said would be fine despite my concerns.

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