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About DanC

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  1. Hi, I'm sure this has all been answered before, I have tried searching but can't find concrete info - I have recently bought a 2012 300 exc. Seeing as my last stroke bike was a piston and cylinder nightmare I pulled the cylinder off it to check everything was OK before I start riding it but I cannot find info to confirm what I need to do next. I have measured the cylinder- Y axis: top = 72.02mm, just above ports = 72.02mm, just below ports = 72.03mm and bottom of the cylinder = 72.03mm. X axis: top= 72. 02mm and its 72.01mm all the rest of the way down. Can I re-use this cylinder or is it out of tolerance? I can't find info on cylinder tolerances. There is no visible scoring and I can still see the cross hatching from honing. The piston measures 71.93mm across the skirt, which is odd because it's stamped 71.925, I guess our calibrated micrometer is being operated badly by myself! This measurement gives it 0.1mm clearance. The piston also shows polishing, not scoring where it runs past the exhaust port, it no longer has the fine ridges it had in this area like it still has on the rest of the piston. Ring end gap is 0.3mm on the top ring and 0.25mm on the bottom ring, still in spec, 0.4mm max. I have read that they need 0.06mm piston to bore clearance but a brand new 72mm cylinder with a brand new size A piston at 71.925mm gives 0.075 clearance. So I'm a bit confused as to what is right. I'm probably paranoid due to a bad gasgas experience last year but I felt like the engine did rattle a bit, and I'm not convinced the fuel in it had the right oil mixed in, hence me taking it apart. Any info would be greatly appreciated Dan
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