Large or Small Gear Case; Johnson 70HP?

[red_chaser]

I've have a 1977 Johnson 70 HP motor.
70EL77S

I am trying to find a replacement for my prop. I was looking at getting a stilleto prop, 17" pitch. On this website there are two options for my engine, a small gear case or a large gear case. I know my prop is a 13 tooth spline but don't know that if I buy a prop under the wrong size gear case will make a difference.

I don't know if mine has a small or large gear case. Will it not be the same as long as it's a 13 spline and 17" pitch?

 

[TwoFish]

Re: Large or Small Gear Case; Johnson 70HP?

From what I can see the smaller gear box uses a smaller diameter 11 inch prop. The larger gear box, 2004 onwards, uses props that are around 13 inch diameter. Diameter not pitch. You can still get a range of pitches for both gear boxes. I would think your gear box would be the small one going by the year of your motor.

You could measure the diameter of your prop to get an idea.

I know Mercury gear boxes work this way.

Hopefully someone with Johnson knowledge will confirm this.

 

[eavega]

Re: Large or Small Gear Case; Johnson 70HP?

I have a '76 70 HP Johnson. That motor has the large gearcase. If you look at a cross-reference, the '77 70 HP is compatible, so I would say you have the large gearcase. The prop diameters for the larger gearcase tend to be in the 13" to 14" range, depending on the pitch whereas the smaller gearcase props tend to be in the 11" to 12" range. If you want to be sure, check your own prop for the size stamped on it. The first number will be the diameter of the prop. If its the standard 17" Pitch prop, it should be a 13 1/4" diameter.

Rgds

 

[tumblweed9999]

Re: Large or Small Gear Case; Johnson 70HP?

In that era..the 70's the small gearcase came on the 15" short shaft 75 H.P. versions. The standard configuration for a 20" 70 hp motor was the big gear case. Im pretty sure they didn't make a long shaft/small gear case for the 70hp until maybe the 80's or 90's. and by then the spline count had changed on the power head.

 

[steelespike]

Re: Large or Small Gear Case; Johnson 70HP?

Prop size is usually found under the prop nut.

 

[jestor68]

Re: Large or Small Gear Case; Johnson 70HP?

Isn't the diameter of a "large gear case" 4-1/4 inches? And the "small" gear case something like 3-1/2" diameter?