rings?

When should you replace piston rings? I bought an engine, hasnt run in 20 years. Pulled it apart and a few cylinders have slight rust that would clean up with a hone. Should I replace the rings? Not alot of hours on engine, no ring ridge but I cant see any hone marks. Wont use tractor much, a few pulls, alittle putting around. I will atleast hone the rust out. What grit hone should I use? Thanks for help!

first of all it would be nice to know what your working on.if you want to know how much wear is on the rings you need to take them off the piston ,with out breaking them. install one in the btm of cyl.as there is little to no wear there. then measure the end gap space with a feeler guage. you need .003 to .004 of clearance for every inch of bore.example- 4" bore would need at least .012 of gap. take note that the top of cyl.has wear so gap will be larger there.wear has to be checked on ring lands in piston also. too much side clearance and ring will not be held flush to cyl. wall. i reused rings twice so for in over thirty years. once in school on a 225 dodge slant 6cyl. because they were new rings in and out many times.the 2nd time on my 6.5 chev diesel because the ring set was 800.00 dollars and the old ones had little wear with 250,000 km. due to crank breakage. it has over 400,000 now. what i did was get a block and crank from auto wrecker and just transfered every thing from the old one to this one. i said i havent patched before but i am now and if it runs for 100,000 i will be happy.its still running to, top end all original also. but back to your tractor hone it out and install new rings as i am sure it needs them. another thing is a gas will show more wear than a deisel.