I mentioned last week that I picked up a bunch of drawings recently, and in the group was a microfilm reel with a rather interesting engine…

Yup, it is indeed an opposed piston engine, and an experimental US Navy engine at that.. And I can not find one single thing about this engine online, anywhere. Gray Marine is pretty well known for the work they did during WWII, specifically with the Detroit Diesel 6-71. Gray Marine would take engines built by Detroit, and convert them to marine use, one of which being the 64HN9 – a 6-71 with a high output governor, used on the Higgins Boat: The LCVP, or Landing Craft Vehicle Personnel.

I cant say I know alot about Gray, but I do know that they would commonly take off the shelf engines (like the 6-71 above), convert them to marine use, and slap their name on it with a new model number.

So, just what is the deal with this engine? Well, I have no idea, and I really hope some of the viewers can help with this one. I have never seen an opposed piston engine like this one. Its a 2 cylinder opposed piston, but note that each crankshaft (4 of them!) drives a bevel gear set, which in turn drives the main center shaft. Holy moving parts, Batman, this thing could almost give a Napier Deltic a run for its money. On the back end, is a reverse gear.

Unfortunately, I have not spotted a spec sheet yet in the drawings. It is not a very big engine though, only 26 1/2″ tall and only about 64″ long. So it could not have been that much of a powerhouse..

These are pretty big drawings, so click on them to see the full size. The one top view had to be spliced together from 4 separate ones.

So, anyone with ideas on this thing…comment or email!