How to precisely identify 1971 Detroit 6-71's

I have just bought a 1978 Uniflite fishing boat that has two Detroit 6-71 and I need to be able to identify exactly what I have. Apparently, there are several types and it would be nice to know what I have. I'm pretty sure these are 2 stroke engines and I'm pretty sure they have Roots blowers. I'm too much of a rookie to identify who makes the exhaust system. Maybe someone can help with that as well.
I can certainly get some photos (or possibly a link to some photos) if that helps.
Thanks for the help.
Jim

Re: How to precisely identify Detroit 6-71's

engine photos will help, also serial numbers and model numbers. serial # start with 6a-------,model # under serial #. just off one engine will do.
yes they are 2 stroke engines, as for the exhaust system that was supplied by the boat builder.

Ok Marv, Here's a couple of photos of the engines.
FYI, I found out that the transmissions are made by Twin Disc, and that they use motor oil rather than transmission fluid.
I'm still wondering about how the cooling system and exhaust work. Surely, these components will need some maintenance, or flushing/cleaning. I say that because I'm pretty sure that seawater is used cool the engine, and I'm pretty sure that anything that comes into contact with seawater will require regular maintenance.
I was told this boat sat for 7 years and that can't be good. I plan on replacing all the rubber hoses and belts, but at this point I'm just beginning to learn about what all is required.
Any advice regarding maintenance is appreciated.
jim

First off, congrats on your "new" boat! I can for sure tell you that you have two pretty sweet looking inline 6-71's! They don't look as if they have ever been started. Do you have any history or documentation on the vessel or the drive train? The engines sure look like fresh rebuilds right out of a DDA affiliate. Complete with the factory approved pea green paint job.

They are naturally aspirated, meaning no turbos nor the maintenance that goes with them. And, while some gearheads and horsepower mongers would not approve, my personal opinion is that you have two of the most reliable diesel engines ever made.

They also appear to have closed cooling systems. This too is something I would want on my boat...if I had one. The coolant is recirculated in the engine and travels through a heat exchanger where salt water is circulated separately to cool the engine. No raw, salt water going through your block and heads.

As Marv said, serial numbers will tell more and with them he or someone else can assist you in determining specifics.

I have more on the subject but I need to go. B Back later
jimmyd

Hi judojim,
just a quick word on your Twin Disc transmissions. Yes they use 40 wt engine oil. It must be C-4 rated or better. Same oil as will be used in the engines. Do not use multi-vis or synthetic oil in either of these components.

If you have oil strainers on the bottoms of the transmissions, they can be removed and cleaned by LOOSENING a hold down bolt and swiveling the hold down plate out of the way. DO NOT completely unscrew those bolts or you risk not being able to screw them back in and transmission damage could occur.

If any fuel was left in the tanks when the vessel was laid up, it needs to be removed and the fuel tanks scrubbed. If you don't do this, you will probably experience trouble with the fuel system.