I'm about to replace the piston rings in my 2005 banshee. So far I haven't been able to find the info in looking for. The rings that I ordered are slightly bigger than the bore of my cylinders so I'm going to have to grind them down. The rings also have a curvature at the ends and come to a bit of a point. Is it imperative that I keep that structure? Or can I grind them flat?

 

IMO, The info you are looking for won't be found because what you are doing isn't done.
If you need rings you use the same size. If you need bigger, you need to get a bigger piston and the cylinder bored to match.
I never just add rings. Always a new piston and rings.

 

So what do they sell piston ring filers for?

 

Filing the ends of rings down can be done on four strokes if you can't get the correct size rings, but two strokes have a cutout at the ring ends which fits over a pin to stop rings turning, so it is almost impossible to file the ring ends correctly on them. I do fit new rings only, if the piston and bore are within tolerances, when checked with a micrometer, but rarely get chance, as usual procedure for our customers is, bike starts using oil, customer runs it until all oil is gone, engine seizes, so needs a re-bore and oversize piston and rings.

 

To file the end gap.

"I do fit new rings only, if the piston and bore are within tolerances, when checked with a micrometer, but rarely get chance"
Yep, that's why I just recommend the new piston/rings.
Merryman, maybe you can comment on him putting a bigger size rings on a stock piston.

 

Pistons are actually 65.5mm, cylinders are at 65.7mm, was wanting to file 66mm rings down. I was wondering about those points on it is all. Is 2mm within tolerance so that I could use 65.5 rings?

 

To answer the ring question, Like merryman said, the rings are notched to fit the pin that's in the piston. Even if you was to file the notches down along with the ends, the rings wouldn't be round once compressed.
Like first reply from me. This is not done.
Techs, please correct me if I'm wrong.

If I'm converting correctly, you have .08 clearance which is out of spec. the pistons are set at .0025 - .003 clearance. Depending on who you ask, .06 is time to freshen.
That would mean that you need new pistons and cylinders bored to match.
I don't know why you would go to the trouble of it all to put it together less than 100% correct.

May I ask what your compression was before you took it apart?

 

 

I gotcha now. I may need to bore to 66. I had 140 left and 150 right. 2 of my rings were twice the gap called for so.