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Gear ratio Johnson 70hp

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DanielKajh

New member
Hello!

I've ended up with some problem and I think you guys can give me a clear answer...

I have problem getting the right prop for my offshore race boat (16ft).

Finally I realized that the problem is the gear ratio... 2.42:1 for my Johnson /evinrude motor.
I need about 1.8:1 or something like that to be able to find a suitable prop for the motor and boat combo.

I have one 60hp Johnson ~1986 and one 70hp Evinrude ~1983. So It would be nice if I don't need to sell these nice motors.

Is the only possibility to sell them and change to a Mercury or similar (which have about 1.8:1) or can I use the gear set from let say a stinger or 200hp johnson in my gear case?

Thank's in advance
 
What size is the hole for the prop and how many splines on the propshaft? Possibly you can get a commercial 4 1/4 gearbox and install a gearset for a 200hp? Or maybe just get the commercial gearbox and then put the larger prop on it? I doubt you can install 1.8:1 gearset in those gearboxes.
 
There is no commercial gearbox offered for the 3 cylinder 70 hp.------And a V-6 gearbox / parts won't fit at all.
 
Ok thanks! No I need a long one... But maybe I can use the internals (gears)

Do do you think that is the only opportunity? What I mean is that 1:8 is not critical the only thing is that 2:41 is way to Mitch for my application..


faztbullet said:
If its a short shaft motor find a nitro gearcase as it has 1.86 ratio and a direct bolt on..
Click to expand...
 
kimcrwbr1 said:
What size is the hole for the prop and how many splines on the propshaft? Possibly you can get a commercial 4 1/4 gearbox and install a gearset for a 200hp? Or maybe just get the commercial gearbox and then put the larger prop on it? I doubt you can install 1.8:1 gearset in those gearboxes.
Click to expand...


I have the 96mm (not sure what it is in US) case and 13splines
 
Have you looked into props from a late 70s 140hp there is a 13 1/2 X 23 stainless part number 0388884 that may work on your gearbox that is a 13 spline shaft correct. That is alot of prop for a 70hp. what is the size of the hole for the prop?
 
Right now iam using a cleaver 13x23" (13 splines) but it's way too little pitch. I would need like a 30" pitch or something to match the boat/ motor combo...


kimcrwbr1 said:
Have you looked into props from a late 70s 140hp there is a 13 1/2 X 23 stainless part number 0388884 that may work on your gearbox that is a 13 spline shaft correct. That is alot of prop for a 70hp. what is the size of the hole for the prop?
Click to expand...
 
Thanks for the help all of you!
I've looked around but it seems to be rather hard to find a high pitch propeller with a "small" diameter. Maximum diameter is 13 3/4" for my motor.
A stupid question. Is it possible to rework the diameter of a let say about 14 1/4" prop down to my 13 3/4" ?
 
Is it the same with the v4 (90, 115hp... small case, ratio 2:1) 1978-1996 or something. Does it fit my shoe or is it totally different? If it's "only" some change of the drive shaft splines or similar many this is a sulution
 
Ok!
Only to summarize...
*It's not possible to use the internals from V-4, V-6 gearcases to change the gear ratio
*It's not possible to mount the gearcase from a V-4 or V-6.

Only possibilite to make the boat go faster with this 70hp motor is to:
*Find a nitro gearcase and modify the drive shaft.
*Find a prop with higher pitch.

Since the nitro case seems to be hard to find I've checked for props.
It seems that the omc have the shooter sst prop with high pitches in the right dimensions. For example 13 1/4 x29". This is a 4-blade prop. Is that a good one for high speed with not so much of the prop in the water..? Compared to a 3-blade prop (cleaver type or similar). I've never tried a 4-blade and I don't need bow lift. The boat is a Dallapieta 16.
Is it ok to go for a prop with high pitch and low speed (2.42:1 gear ratio) instead of using higher speed on the prop (example 1.8:1) with less diameter and pitch? What would be the difference in drivability?


*Or change to a v-4 motor if the boat can handle it...
 
You might look into whether a gearcase from an early V-4 will adapt.-------Say a 60 /75 hp manual shift type or even an electric shift.-------Motors would be from 1960 to 68.--------Prop spins very fast on those.-------Nearly 1:1 or 23 crank revolutions for 20 prop revolutions.
 
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4 blade will decrease top end. Can you find a prop shop that will custom fabricate a prop? you could find the highest pitch prop for the 3 1/4" gear case and have them re-pitch it. If you can't find it, build it.

KJ
 
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