open your saved assembly. we changed piston and connecting rod. if solidwork ask you for rebuil, please confirm that. now insert this part
firstly make coincident this surfaces
use matte command and click on this surfaces.
make this surfaces coincident. confirm that
insert this part
make this surfaces coincident.
and this surfaces..
finally make this surfaces conctric. now add 5 more new part and make same things for them
your engine must be look like this