And the fun continues! 3rd box of parts just showed up, good news is it was in better condition than the last 2. Cams look good so I called Millenium Technologies to see how much it would cost to fix the cylinders. Bad news is the cost is $1600us ($2400 aud). And of course there are no OEM pistons or oversized OEM pistons. Chinesium pistons scare the hell out of me. They weigh a lot more than the OEM pistons, so I would also have to re-balance the crank in addition to poor finish. A tiny bit more info here https://2fiftycc.com/index.php?threads/look-what-the-postman-brought-today.9525/page-24#post-130233 not that it likely matters.
Can you squeeze 0.875mm overbore out of the cylinder walls https://www.daytonaindonesia.com/product-detail/jupiter-z1-50.25-blank-head/26 Otherwise Mike Norman built Dave Moss his race engine for his MC22 with pistons from ebay - pistons worked fine, rings loss their tension a bit too quickly apparently - the ebay pistons are the same ones available on aliexpress - IIRC and available in oversize https://www.2fiftycc.com/index.php?...2-racing-in-california.8371/page-2#post-94334
Four oversizes available - get in touch with either Mike Norman or Dave Moss to get their opinions on these - Mike used them on the Dave Moss engine build https://www.aliexpress.com/item/32277416585.html If you trawl through these photos you'll find some with pistons which have 75 etched on them - I suspect that Mike went to 49.25 oversize in that build as there's also photos with what looks to be less material on the sleeves between some shots among the albums https://www.dropbox.com/sh/x1m7hzedjmceysg/AACtUSSb5MLZDe8Hbr3DoJFQa?dl=0
Any references on using those pistons? While the bore size is "near" I'd have to wonder about other specs. Mike Norman informed me the sleeves are cast into the cylinder, but we didn't go much beyond that.
That's in this post https://www.2fiftycc.com/index.php?...2-racing-in-california.8371/page-2#post-94334 Now this might sound crazy, but if you went to 49.0mm AND if ZXR250 OEM rings are available and perfectly compatible in all respects you could potentially use those This image album from Mike Norman on the Dave Moss build has him cutting the valve recesses https://www.dropbox.com/sh/x1m7hzedjmceysg/AAAnNGYQUYFZvmZhTAdhyDg4a/Moss MC22 2017 Build?dl=0&subfolder_nav_tracking=1 This image has the .75 stamped into the piston clearly visible https://www.dropbox.com/sh/x1m7hzed...oss MC22 2017 Build?dl=0&preview=IMG_5515.JPG