CT3-  I purchased the piston and rings as a set. I installed the piston arrow to front ( exhaust). The rings are throwing me for a loop. I read the green ring goes on top but it is extremely tight & I'm not sure that I can compress it fully to slide the cylinder over it. Is the green ring for the top? I have the rings installed with the longest edge on bottom as my pins are on the top of the groove. 

One issue is making sure piston matches the rings...  some aftermarket parts are interchangeable with OEM, some aren't. 

Piston likely has a "K" stamped in the crown?  Rings are stamped near the gap.  Any stamping on Yamaha Keystone ring always* faces up. 

If I remember correctly, Yamaha rings have a "1" stamped in the top ring and a "2" stamped in the bottom ring.  The ring expanders are also different for top and bottom...  difference is shown in manual.

It sounds like you are trying to install a "square" ring into a "keystone" groove.  be careful so you don't damage grooves.  

Pictures of your piston crown and rings might be helpful...  and are you working with a matched piston/ring set?  OEM or aftermarket?  Piston and ring part numbers can get confusing so post those if you can.   

Edit *Enduronut asked me to clarify this.  I added the clarifier "Yamaha Keystone" and removed "always".  Other types of rings (Dykes for example) may not have the markings on the top.

Your message makes more sense. I found the numbers and the green ring has a 2N on it. Numbers up of course. The other has a faint 1 on it. These are OEM parts and sold as a set. I kept reading the green ring was for the top groove but it was so tight it made no sense. I have not forced the cylinder so no scratches yet. The green ring goes on the bottom. I was right the first time but all of the info said I was wrong. Thank you for this clarification.

Here are ring markings...  took a while to get my old camera to show them...  but camera sees them better than I do with a magnifying glass! 

These are both marked "1N" which means there isn't a top and bottom difference in this application or someone mixed the rings up with others since it's an open box.  The size is on the other side ".25" is first over.

 




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The cylinder went on as I remember. The top ring was 1 ( black) with letters up and the bottom ring was 2 ( green). It took a little tap to fit it to the case. Thank you, I can ride with a little more peace knowing I am not ruining a top end.- Karl

I see you figured it out...  Great!!!

But the belief about Yamaha selling them as a set can trip you up...  unless it's a piston and ring set still sealed in the factory box.  I've found a few sets of rings and sometimes pistons in open boxes that aren't the right parts. 

One more thing...  keystone rings have a slight taper on the top surface.  Ring groove tapers to match.  So a square ring won't go in.  Easy way to tell if ring groove is keystone or not is to try to put the ring in the groove "backwards". If groove is keystone (tapered), ring will only go in a tiny bit "backwards".  If groove is square, ring would slide all the way in. Also Yamaha piston should have a "K" on the top.

On Keystone rings, outside edge of ring is slightly thicker than inside edge.  Hard to see, but you can usually see or feel it... or certainly can measure with a caliper. 

It's important that rings match the grooves...  you can install keystone rings in square grooves but that can lead to catastrophic failure.  So I always check. 

Here's the piston for those rings...  0.25 oversize, check.  "K" on top so should be keystone rings, check.  Both rings have same markings so both grooves should be keystone, check (by trying to insert rings into grooves "backwards" and seeing they barely go in groove, see pic below.)  Inspect rings and they are both tapered keystone rings, check.  All should be good...  but don't forget to make sure ring gap in bore is not too tight.

 

Enduronut will know for sure but I think the green rings are chrome plated with a teflon coating?  The plain rings might be cast iron?  Yamaha came with chrome rings but offered cast ring(s) as an option for oversize sets.

I apreciate all of the info. I bought the rings and piston together OEM and they came in the original box, so I was confident they were a set. I was within tolerance so Endoronut sent me a std. package. Thanks again.

You’re welcome. I know I gave you way more info than needed. This kind of thing comes up fairly often so thought I’d use the opportunity.   

If I would have known Enduronut sold you the parts I wouldn’t have questioned them. eBay stuff can be sketchy reboxed crap or even the ad shows NOS OEM boxes and they send you a modern Chinese knock off set.