re-sizing rings

Filing the Ring Gap

When you receive your new rings, you will place them in the cylinders and measure how much clearance is left at the ring gap at various points in the cylinder. Slipping feeler gauges into the gap lets you determine if the clearance is sufficient and matches your tractors suggested specifications. To increase the ring gap, spread the gap enough to insert a file and move the ring back and forth occasionally checking the gap in the cylinders till you reach the desired clearance.

http://www.ytmag.com/articles/artint10.htm

I understand the process, I'm just worried that since the rings are already a little bigger, they might have too much stress when they are in there.

If you do end up taking off that much, I would recommend a ring filer meant for the job. Because your taking off so much, you need to make sure that the gap stays consistent and straight.

I understand what's involved in "gapping" the rings, but I'm asking if the size I have (0.5mm/0.020") is too large to adapt to the stock bore.

Think of an extreme case: 75mm bore and 175mm rings. I'd have to cut off 100mm or so out of the ring, leaving me with a little less than half a circle which wouldn't be able to bend to fit the bore, even with the right length.

Now, replacement rings can come a little off in size, and you can file them down to make them fit just fine. How big is too big? If I file these rings down, I'll have to take off about 1.5mm... it doesn't seem like much, but I don't know.