I have a 31p777 18.5 hp mower. Its only 2yr old . It broke the piston and crank. I need to rebuild it , I also need a shop man, to do this . But where do I get it . And where is the best place to get parts...

Briggs and Stratton Lawn Mower Engines - Small Engines & Outboard Motors - Briggs & Stratton

Engine breakdown diagrams are free. Manuals are collections for many different models. There is a nice FAQ troubleshooting section as well. You may need some special tools as well.

Prices were about the same as my local dealer. With my local dealer, I didn't have to pay postage.

When you say "ONLY" two years old, has it been two full years since your purchase date? If not, and it is not in commercial usage, you may be able to have it repaired under warranty. Although this failure is usually not covered by warranty because they will find some reason of neglect on the owner's behalf. They may say your air filter was dirty, etc... but if you have a shop close by it may be worth the try.