Can someone break this down for me?

I see a lot of post about engine rebuilds... What does that mean exactly? Replacing the pistons? Also, why on these post are people boring out the cylinders to use a bigger piston...? Why not just replace the piston with the same size piston?


Can someone recommend a book or something?

 

Rebuilding is just tearing the engine apart and replacing worn out parts. Boring out the cylinder removes any deep scarring and scratches so the piston rings will seal against the cylinder better. Boring the cylinder out is also like putting a bigger motor in it, and we all know what a bigger motor means.

 

So because you have it tore down you might as well bore the cylinder to remove any scarring etc... and because you bore the cylinder the hole is now bigger and you need a larger piston?

I guess my question really is: Do you need a larger piston because you bore out the cylinder or could you bore out slightly and use the same size piston?

and thanks for your reply.

 

When a cylinder is bored, you buy the piston and the shop bores and hones the cylinder to the size of the piston. We're talking .003 clearance.
If the piston to wall clearance in in specs, then boring isn't needed.
This is usually known as "freshening up the top end".
IMO a rebuild is when the motor is disassembled and new bearings, seals, gaskets are used.