Namura Piston

[Phelps]

dude i have been running numura's in my alky bike for well over 10 hours of hard riding. i have seen one numura skirt break in a cr250, but you should have seen how the bike was ridden. pinned in the corners with the brakes locked up and sling shooting out. yeah no shit they wont hold up to a constant 12k...... neither would a stock (art) piston or any other cast style for that matter.

[James-26]

Yea, I have read mixed feelings about these pistons. Some will say the pistons are great while others say to stay away. I was reading just last night where a guy said he only had 3 hours on his shee and one of the Namura pistons let go and fucked up his case. So IDK what im going to do. Maybe run them till winter or just suck it up and rebuild it right.

[zachmw]

I wouldn't stress out about it, if it was me I'd ride the piss out of it and when the time comes, replace them with what ever.

[midlifecrisis]

I wouldn't stress out about it, if it was me I'd ride the piss out of it and when the time comes, replace them with what ever.

X2, these things are pretty simple to rebuild, so ride it out for the season then do what you need to over the winter. I had never rebuilt a 2 stroke otor before I bought this thing in Februrary of this year. With help from these guys, and a clymer manual, it made it pretty simple, oh and before you need it, buy a correct flywheel puller, so that you have it.

 

Yeah the size of your present pistons in case you havent figured it out, are 64.75mm, and usually each time you resize it is increased by .25mm, up to 66mm, then you can resleeve, and start again.

[James-26]

 

Yeah the size of your present pistons in case you havent figured it out, are 64.75mm, and usually each time you resize it is increased by .25mm, up to 66mm, then you can resleeve, and start again.

 

So my cylinders have been bored .030 over? .040 equals 1mm over correct?

[James-26]

Well turns out that my pistons are not Namura they are WSM cast pistons. I have my engine tore down and googled the number off the top. I called SWM and I was told that there cast pistons are the same as Pro x pistons.

[midlifecrisis]

Well turns out that my pistons are not Namura they are WSM cast pistons. I have my engine tore down and googled the number off the top. I called SWM and I was told that there cast pistons are the same as Pro x pistons.

Yeah the .010 over is .25mm over , .040 over is 1mm over and so on and so forth. As far as the cast pistons vs. the forged, the cast pistons expand at a different rate than the forged and make them more unpredictable, although I believe that a stock piston is also cast.