Hi all,Getting into the rusty, crusty, CT1-C motor. I got the bike to run a few weeks ago. it started up fairly easily, got through the gears but really bogged when under load; 2nd to 3rd; top end is worn says me.. I am still a novice but learning quickly. Can anyone decipher the numbers on the top of the piston? I would like to replace it and will take the head to shop. What would be the next size bore and piston for this head? 
Looks like we can't load pics at this time.
Looking at the top of the piston; to the right side of the arrow is a 5 ; 14 ; K
Opposite the arrow markings are the numbers 9 6 3. This is a Yamaha piston. I am not sure if it is the original piston or not.
Many thanks.

 

I let the machine shop determine the size required. Sometimes the wear and tear on the cylinder is deeper than the next size up and might need to go 2 sizes up.

Also you have the coolest avatar.

Thanks very much for the reply. Are cylinder bore jobs done to standard increments?  Meaning  Honda bore jobs are different  than Yamaha bore sizes, etc.. The cylinder is pretty smooth. No deep scratches, etc. I am concerned that they bore it to a size where I can't get a piston and rings. Again I am a bit new to this.
Thanks for your help.
Thanks for the avatar compliment. Its a selfy..

The shop will bore to the point of clean and smooth cylinder wall and then increase as necessary to match the corresponding available size up.


Sometimes they are able to determine the size necessary before boring.

I believe a competent shop will measure the wear in your bore currently ,
advise how much bigger you need to go to clean up a fresh bore .
Then you obtain piston and rings of the appropriate size , and then have the cylinder bored to
suit the piston , giving correctly specified clearances .
You don't bore the cylinder , and then go looking for a piston .

Good advice. I will do that.
Thanks for the help.
 

I.m guessing it's still standard at 66mm. I see you say there's a 96 number on top so basing my decission on that as denotes some sort of std clearance with the smaller numbers past that. How bad is the cylinder to look at. Can you run a new std kit. Bogging under load doesn't neccesarily mean needing a rebore. Hows compression feel on the kick start if you lean on it, Should have good bouncy comp on a 175. You say goes through the gear but boggs on 2nd & 3rd, does it pull 4th & 5th. Just trying to save you spending heaps then finding the exhaust is blocked. I'm in exhaust mode mostly lol when it comes to performance or lack of. Not always right though.

Those markings sound like standard bore Yamaha piston so not too likely it's been bored way over. 

Good advice given...  problem is finding a competent shop these days.  Might be worth shipping it to Bill Bune or another reputable shop.