@cancer4u28! A word of advice.
If your bike is emitting while bluish smoke, then its better to get the whole head rebuild, which will include:
- New valves plus valve seals
- New piston
- New Rings (make sure to get Japenese rings)
It may look like 'unnecessary' and the mechanic might not also tell you that, BUT ... if you don't change them this time, your new rings will not last you more than 6-8 months, and then you will have to get the head opened up once again.
Make sure you DO NOT (in any case) get the Head re-bored to bigger. If its the first time you are getting the engine opened up, then you may not need to rebore it (re-bore will require a bigger size piston to fit in, which will technically be an "altertion"). IF it comes down to get the engine re-bore ... GET A BRAND NEW HEAD.