I recently bought a 1959 Johnson motor with a prop slip. It currently only goes 4 Mph. It loses it at High RPM's. Does anyone have any ideas on what is wrong with it?

Thanks a lot!

Do you know what a shear pin is? Have you checked it? pull the prop off,a hole in the shaft should have a brass pin in it that is lond enough to fit in a indent in the prop. pin is about 1-1&1/4 inches long.

Yes I am aware of what a Sheer Pin, it is in perfect condition. Thanks though.

Spun hub? Take a Sharpie or White out and put a mark that extends across the prop and hub of the prop. Go run it. If the marks are no longer lined up, your hub is spun. You can get it fixed or just buy a new prop.

if that doesnt check out ,wondering if you have a 16 inch motor on a 20 inch transom///?

Sounds like a spun hub to me.

marine_man

MM I was going to GUESS that but Do sheared props have the inserts?? I guess I dont need to ask you said it. but I remember once replacing a sheared prop, with the shop saying their not repairable??

Ah.. now that I think about it some more you're right.. no hub on a shear pin motor (the whole point of the hub was to go to a splined prop shaft and get rid of the shear pin). Good catch Sparcebag.

Hm... since it's not that, it could be like primetime 49 said, a short shaft motor on a long shaft boat, or perhaps lower unit issues.

What does your motor do in reverse?

marine_man

You're assumptions are correct, no hub to slip on that motor.
Has the gear lube been drained and examined? Any shavings or burned smell? I've seen the drive shaft splines (going into the powerhead) slip also.

Thanks for all the input guys! I took it out this weekend and it starts right up, and I was going about a solid 4 mph's. But when I took it out of the water the lower unit was leaking oil. I think my problem is pretty big. The lower unit may be cracked or something pretty bad. Not sure what to do now. Thanks again!

I'd take it in.. have them pressure test it and see where it goes from there.

Good Luck!

marine_man

yea, Thanks!

I hate to disagree with the experts here but I'm sure the older props with the shear pin hub used a rubber cushion inside the prop. I have owned these motors and have personally spun the hub. At least have that checked out.

You may have other issues as well with the oil leaking and that absolutely needs to be addressed. A new lower unit will cost more than the motor is worth.

I stand corrected, hydro is right.