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I have seen a few discussions on this site, curious about how these pistons are holding up, if there are any fitment issues or quality problems with them. Are these a real option for the 1300's or am I better of scrounging for factory oversize parts? My bore is currently standard.

If you're referring to the Japanese company selling well cheap pistons on e-bay, I can't comment on the Z13 ones, but I have a friend who fitted some to his H1 and was very pleased. I also fitted a set in an XS650 and they were fine.