I have an AT2 that I'll be putting new rings in. I happen to have a set of NOS rings for the earlier 70/71 model which has a different part number than the AT2 . The number for the rings I have is 479-11601-00 and the AT2 number starts with a 314 and/or 316. According to Partzilla, the set I have won't fit a 1972 but does anyone know if this is really the case? Did they change piston design between the AT1's and AT2's? Since I have these rings laying around, I was hoping to put them to use. Thanks for any help.

The 479 prefix rings are "alternate parts" which might actually require an "alternate piston" to match. Yamaha made a lot of changes over the years to ring designs.

And yes, the piston design definitely changed in 1972 as it's a reed valve engine with windows in the piston versus the 69-71 that had a solid skirt piston. This doesn't mean the rings won't work... and the 479 prefix is for a 74 RS125 so there's a chance they "could" fit? Because there's also the unknown of exactly what piston in in the bike now? Even if you bought the exact rings listed they still could be wrong if piston was swapped over the decades.

One caution on the 314 and 316... both WILL NOT fit. 316 is the AT2 prefix and 314 is the CT2 prefix. If you buy 314 rings they will be for the 175 and will be way too big. This is a common problem as the parts lists are shared among similar models and when they "digitized" the lists, the important info like this was often lost. And it's why you'll see "magic" pistons and rings on ebay advertised to fit both the 125 and 175... that's impossible so you have to do your homework and model code prefix of the part number is an important clue.

My suggestion is to post up detailed pictures of the piston and rings you have in the bike and one of the experts might be able to identify which rings you need... or just contact Enduronut and buy a matched piston and ring set for the bore size you need.

Good luck!

Thank you, that's good information. Funny you mentioned the 314 and 316 confusion, that's exactly how I ended up with this ringset. I originally ordered rings for a CT1 but because of the alternate numbers, I ended up with 125 rings which I didn't realize until I went to install them.
Anyway, I don't have the cylinder off yet but when I do, I'll use your suggestion and post some pictures for the experts to decipher. Thanks again for your help