Early 60's 75 HP Johnson general questions

[ci2hi]

I have a 1963 75 HP on a 1965 Shell Lake and I am looking to put a different prop on it. As I was digging through my spares I noticed that some of them have a small diameter hub and some have a larger diameter hub. Upon searching I find out that both seem compatible. I am curious as to why they made them two different ways. Second question: I replace the coil in the magneto from a 1960 parts motor. Bear in mind mind is a 1963 model. Both had the same ignition with internal coils.I also have a 1961 75 HP and it has the newer ignition with the external coil. I'm curious if the ignition systems were an option. 1960 had old style. 1961 new style. My 1963 has old style. All of them are mechanical shift and not electric shift. Maybe using up old parts on a newer model possibly? Thanks for any information you can offer.

 

[southkogs]

Moved ya' over here ... this is an outboard and not a stern drive, correct?

Welcome aboard.

 

[racerone]

Boats were getting bigger.-----The small hub prop helped get boats on plane.------Not an " old parts on newer motors " scenario.-----This was 60 years ago and ideas / public demands were different than the lazy folks today who demand " push the button " technology, with a computer to do the thinking for them.

 

[ci2hi]

Thanks for moving it over. I'm new and boy is navigating this site requiring a learning curve for me. So the small hub prop was probably a little easier to spin, I take it. Still stumped on the ignitions. Now to try to find a post to help a fellow boater with low RPM problems that I posted today on adjusting his quadrajet carb.

 

[racerone]

The magneto did not need a battery to run !----Electric start was not always demanded by folks 60 years ago.----Times were different then !!

 

[ci2hi]

The first four cylinder ignition system had the internal coil. Correct. No battery required. Then a year later is the one with the external coil. At least this one has it. Then, for some reason, the next year model has the old original system. . That's all I'm wondering. Like if you were to see points on a late 70's 20 HP. A reversion in technology. Even though these 75's have a recoil starter, I imagine it was mainly for backup and most anyone that had a 75 had electric start. Weren't they standard starting with the 1958 50HP? I know times were different then. I lived it. I still am, obviously. LOL

 

[racerone]

They offered BOTH systems for a number of years.-----Folks made a choice when they picked a motor at the dealer.----Delux or simple.-----Check the parts books.--End of the story !

 

[jimmbo]

Of the 6 props offered by OMC for that engine, 4 had the larger hub, used a huge Prop Nut, the other 2 props were the small hub and used a smaller prop nut. One of the small hub prop was quite common to see, the 10 X 9 1/4. The other, a 10 X 11 was rarely seen as they was also a large hub 10 X 11, there might have been a different blade shape involved. The other large hub props were 10 X 12, 10 1/8 X 10, and finally a 9 1/2 X 10. The small hub props usually show moderate Cavitation Burn on the low pressure side of the blade near the blade root. Another oddball design by OMC during that period.

The engine was was offered with either Battery or Magneto Ignition. Post 61, it came down to which Shift system the engine had. Electric Shift models got Battery Ignition, and a regulated Alternator Charging System, while the Mechanical Shift got the Magneto. A DC generator was a Dealer installed Option offered

 

[ci2hi]

Jimmbo, Thanks for your detailed, informative and civil answer.