Model Engine Company of America
Which way does the piston & cylinder go back in.

Some engines have transfer ports through the piston as seen here and the picture below. This is a Schnuerle ported RJL K.61 and it has a large transfer window in the piston for the boost port. These ports in the piston are always opposite the exhaust. If you were to put this piston in backwards all the crankcase compression would leak out and the engine will not run.


READ ABOUT RING INSTALLATION and end gap location.

This is a loop scavenged, cross flow piston & cylinder out of a K&B 40. This has the transfer holes in the piston and cylinder. I refer to these as cheater holes because you can increase the flow through the bypass without altering the crankcase casting. This trick has been done for 60+ years.
You can always tell a loop scavenged engine by the baffle on top of the piston. On a loop scavenged engine, the baffle ALWAYS goes opposite the exhaust ports.
The exhaust port or ports are always symmetrical and are ALWAYS THE HIGHER PORTS. Closer to the top of the cylinder. Like this example you can see the "cheater holes" on the left and the higher exhaust ports on the right.

Sometimes there is no web or bridge between the exhaust ports, so you only have one wide, rectangular port.

WRIST PIN with pad

Usually the wrist pin with a pad will have the pad opposite the exhaust. The pad must always run against a portion of the cylinder. I can not pass over an open port. If it does it has the possibility of popping into the open port and causing damage.

WRIST PIN with snaps

This wrist pin can be installed either direction.

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