If you are wondering why we do not teach Rod ,piston, or value, work .

 This is our explanation! Internal repair on different engines have so many different various.

You would need expensive special tools for these different task for repairs.

70% of all small engines have aluminum cylinders. In order to rebuild a engine with an aluminum cylinders 1st you have to disassemble the engine next you have to check the cylinder wall to see how worn it is. It will have to be bored out because of being aluminum. The piston has steel rings and the cylinder wares because of being a softer material being aluminum. Therefore not being cost efficient  on repairing a engine prices on today's market