Engine swap

[helodog]

Can I put a 21 size engine in a boat that has a16 size engine with out having to change anything ?.

[Ron Olson]

Nope!
You'll have to change a lot. The motor mount is different along with the flywheel, drive coupler and plenty of other parts. Most of it depends on what you are planning to drop a .12 into. Most under .21 hulls won't take the stress of a good .21 motor, especially a plastic one.