Old Johnson 10hp trouble
jtroop
Posted 9/19/2007 6:29 PM (#275735)
Subject: Old Johnson 10hp trouble




Posts: 177


Location: Cohasset, MN
I have a 1955 Johnson 10hp that starts and runs great but I've begun to have a problem. Sometimes when pushing my 14ft boat on plane (full load) there will be a "bang" that sounds and feels like I hit a rock with the lower unit (I haven't). What might this be ? Backfire ? Gear slipping/missing a tooth ? Any idea's ? Sure makes the boat trip less than serene !
Tim Kelly
Posted 9/20/2007 8:13 AM (#275811 - in reply to #275735)
Subject: Re: Old Johnson 10hp trouble





Posts: 358


Location: London, England
Possibly the prop slipping on the driveshaft?
MuskieFIRST
Posted 9/20/2007 8:37 AM (#275819 - in reply to #275811)
Subject: Re: Old Johnson 10hp trouble





Posts: 507


I agree that could be it or something similar.
VMS
Posted 9/21/2007 8:35 AM (#275975 - in reply to #275735)
Subject: Re: Old Johnson 10hp trouble





Posts: 3508


Location: Elk River, Minnesota
If it is a big "clunk", I would highly doubt a prop slip... A motor of that year uses a shear pin. So..if the pin sheared off, it would not spin and no forward movement would happen.

I'm wondering if it isn't something with the gears in the lower unit, though... Might be missing a tooth here and there, and when the gears hit "just right"...the clunk happens. It might be simple as a shift linkage adjustment (if that motor has that capability) too...but if it's in gear and on plane, that doesn't sound like it would be the problem.

A tell-tale sign of gears missing or broken would be to drain the lower unit and see if there are pieces of metal in the gear oil. If so, it's rebuild time if you want to keep a beautiful timeless piece of engineering going, or it's time for retirement and display... Parts should still be somewhat available for the motor if needed (from a place such as twin city outboard)

Steve
jtroop
Posted 9/21/2007 8:58 AM (#275979 - in reply to #275735)
Subject: Re: Old Johnson 10hp trouble




Posts: 177


Location: Cohasset, MN
Another way to describe it - it's like someone hit the bottom of the boat with a mallet.

I'll check the LU oil, etc. Thanks for the idea's, everyone.