FL motor case and an EL motorcase

[Paultrehberg]

Is there any difference between a knucklehead FL and an EL motorcase?

[Robert Luland]

One in the same. Bob L

[Rubone]

From '41 up they are completely interchangeable, however there are differences on the earlier EL cases having to do with the inside diameter of the casting. From '36-'39 the casting is smaller inside for the smaller diameter flywheels. The '40 cases changed to a larger ID but also had minor exterior differences. The FL came out in '41 and from late '41 up they share the same cases. It is easy to switch internals on later types. The only other identification other than the VIN is a number "7" stamped on the rear motor mount area to allow factory workers to ID what engine they had as the VIN was not placed on the cases until the build was complete.

[Jerry Wieland]

The 40 EL cases still used the early small diameter flywheels but had the baffling removed from the cylinder throats. FL and EL in 1941 got the big diameter flywheels.

From '41 up they are completely interchangeable, however there are differences on the earlier EL cases having to do with the inside diameter of the casting. From '36-'39 the casting is smaller inside for the smaller diameter flywheels. The '40 cases changed to a larger ID but also had minor exterior differences. The FL came out in '41 and from late '41 up they share the same cases. It is easy to switch internals on later types. The only other identification other than the VIN is a number "7" stamped on the rear motor mount area to allow factory workers to ID what engine they had as the VIN was not placed on the cases until the build was complete.