Belt driven vs Direct drive

[brettportzer]

One of the nice things about these Detroits, as I understand, are the accessory drives.

I have 6-71 naturals. J&T marinization from 1972.

So, my alternator is on the back of the engine, and it is pulley driven from the outboard accessory drive.

The tach sender comes from the inboard accessory drive.

The raw water pump is pedestal mounting at the front of the engine and driven with two belts from the crankshaft pulley.

Question is, why aren't both of these things just direct drive, and on the back of the engine?

Lots of direct drive water pumps turn up on a search, but not really much in the way of direct drive alternators.

Seems like that would be a good way to have a higher output alternator?

 

[Captain Ralph]

I managed a a boat with 6-71s and the alt & raw pump were on the back of the engine. All was sweet.

Alternator draw backs; There is only two models of alternator that fits the direct drive adapter. Leece-Neville, now owned by Prestolite is the more common. It is expensive.
The alternator turns at engine speed. No belt/pulley ratio to speed up its rotation speed.
Enter Leece-Neville again with their special slow speed excited windings. AND, no high amp output.
When you needed high output, direct drive alternator, you bolted on a Delco 50DN.
Larger than the blower and nose-bleed expensive.

J&T not only was a performance packager, they provided boat assemblers cost reduced engine packages also. J&T may have left your configuration to the boat assembler on how options mounted or were packaged. Drop that expensive Leece-Neville and hang on a cheap 30SI.

Remember, those are the only PTO options on the straight 6-71. Where would you mount an air compressor or stabilizer/thruster pump?

Long live the 6-71. A wonderful creature.

I remember reading an in line 8-71 was on paper and waiting for a green light.
Like the other in line gas 8s of the day, it would be a smooth and powerful engine.
Sadly that was dropped. multiple engines were crash-boxed together already and the V blocks were in the near future". Rats...

 

[bostonhatteras]

I remember reading an in line 8-71 was on paper and waiting for a green light.

A crane would be needed to lift the head off.

 

[Captain Ralph]

A crane would be needed to lift the head off.

No, it was real cool. Two 4-71 heads.
Artist renderings and sketches. None built, no pictures.
It really looked like two 4-71 blocks end to end but one block, one piece crank, not a clue about the cams.
I'm guessing but one big blower??

Just the great ideas that was bouncing around back then.

Now were broadcasting ammonia all over ourselves with these new little engines and motors. Blah