Quick newbie question. Just had the piston out of my ‘76 DT400 and all looks good, going to get the cylinder honed so want to replace the rings.  Piston has a 50 stamped on the top, so I’m guessing at 50mm oversize. Is that right as the other part number inside is too short to determine (50002) and measuring the skirt gives 85mm which is not on my parts list (starts at 85.96)?  I do have a new set of rings that have been sat in a box since I bought it 20 years ago. They look exactly the same size as the ones I’ve just removed but the box they’re in put them at .25 oversize....I think I’ll order new ones so as to be sure.......once I know the size!

50 is the second over piston, .5mm

Thanks, thought as much!

I won't tell ya what i did when short of rings--& money. Oh, ok then, joke's on me. My YZ465 was on first over 0.25 but i had new std rings so in they went. Had full comp & ran 100 percent. Old ones were very worn out though. End gap's not the big thing--it's wear as they go past each port especially the exhaust which is the big one--or even bigger still on a 465.