Can you please tell us what 1980 80cc 2 stroke you own so that we may gear our answer toward your bike? Is this a bike you ride or a child rides? It sounds like you have a family, but ride an 80cc bike. How tall are you?? How much do you weigh?? Most folks don't ride an 80cc bike is why I ask.
The point of taking the measurements on the ring end gaps, cylinder diameter and piston diameter is to know where they are at compared to the factory specification. For example: You buy a new trail bike and ride it for one year. At the end of the year, you take the top end apart and measure the parts. If the ring end gaps are close to half way worn out, then you know that at the end of the following year, it will be time for new rings. A common practice is to replace the rings, then next time replace the piston, piston pin, small end bearing, piston pin circlips and rings the next time. Different bikes have different maintenance time frames. I elieve the new four stroke 250cc MX bikes generally have a maintenance time frame of ring replacement after 15 hours at race pace. They are designed for high performance. Top fuel dragsters usually need to be rebuilt after every run down the track. Someone feel free to correct me on that, but I am close.
Like TRAIL said, it depends on how often you ride and how hard. You say you have a 1980 80cc bike. If it is on its original rings and piston, then we already know it isn't a MX bike seeing frequent action over 25 years. The piston, crankshaft, etc. would have broken by now, destroying the cylinder, maybe head and/or crnkcases, etc. All these are expensive parts. Some people want the best performance from their engines, some try to keep them from blowing up. I hope you are not about to try a big jump on your bike, because it WILL blow up with your non-maintenance style.
