440 Chrysler Marine Distributor Problems
(this would also apply to 383, 426 wedge and RB440 marine engines)
Chrysler Marine called them “thrust collars”. These "spacers" fit between the iengine block and the distributor and raise the distributor up ¾”. There are 3 different lengths depending on which marine engine you have. They were necessary on the starboard engine of twin-screw boats and in any engine that had the rotation reversed from automotive. The reason is that when you reverse rotation, the distributor thrust is upward rather than downward like GM and Ford and distributors aren't designed to handle upward pressure.
The port, or standard rotation engines like automotive, don’t need this thrust collar and can use a distributor length of 4”, on 440s. Distributor length is measured from the mounting flange on the distributor to the bottom tip. The reason CM used it was to keep marine distributor lengths all the same at 4 ¾”. Thrust collars are necessary on reversed engines but not necessary on standard rotation engines.
AAA MARINE PARTS WHOLESALE (aaamarine.com) usually has both, and you can mix them or use the thrust collar on both engines and 4 ¾” distributors-it’s your choice. firstname.lastname@example.org