'77 Johnson 25 hp "slipping"

[csgrizz]

Hello, this is my first post and let me say, it is a great forum, wish I knew about it years ago.<br /><br />I aquired a 1977 Johnson 25 hp (tiller)that I hoped to use as a my new duck motor. The guy who had it before me said it was a great motor, but had a problem "slipping out of gear"<br /><br />First thing I did was put it in the test tank, and NO problems whatsoever.<br /><br />Took it to the lake, and just after hitting the throttle it "slipped", RPM's jumped up, forward thrust went down, I could take it down to idle speed and it would work fine, but couldn't put a load on it.<br /><br />Note: The shifter never popped out of forward gear.<br /><br />I removed the prop and the sheer pin is bent away from the motor (towards the prop) and it is worn off a bit on the side that faces the prop.<br /><br />There is no rubber bushing, only a metal bushing and inside the prop, the gold "piece (hub?)" has a couple shiny circular streaks on it, where it has been rubbed, but nothing major.<br /><br />Any ideas??? Where to start or where to go?<br /><br />Thanks in advance for any info/suggestions.<br /><br />Corey.

 

[BF]

Re: '77 Johnson 25 hp "slipping"

Hiya & welcome...<br /><br />at first when I read "slipping" I thought of the clutch dog in the lower unit. But those make a clunking type noise (sort of like is 1/2 in gear). From what you wrote it sounds like your prop might be no good. Maybe the hub is loose and spins. You can take the prop off and mark a line across the center hub and onto the outer part with black marker. Run motor to make it slip. Then take prop off and see if the line is still lined up or if it has slipped. <br /><br />I'm not sure, but I don't think you can re-hub those props... but new or used ones aren't that hard to find.<br /><br />Also, do a search on "clutch dog" and read some of those threads. See if that sounds like your problem.<br /><br />Good luck.<br /><br />Brent

 

[BF]

Re: '77 Johnson 25 hp "slipping"

oh, and something is whacky with the shear pin. It should be straight and should turn with the prop (no wear marks/flat spots)... maybe it's the wrong one for the motor? You should replace it and buy a few spares at the same time.<br /><br />Brent

 

[surfdaddie]

Re: '77 Johnson 25 hp "slipping"

I would try replacing the clutch dog and the propeller drive shaft that might be messed up. The yoke assembely might also be seized

 

[grizzlyadams]

Re: '77 Johnson 25 hp "slipping"

check your clearence. motor shaft could be to short for your boat. ran into the same symptoms you disribed on a boat i just bought. had to cut the transom down six inches. solved the problem

 

[DJ]

Re: '77 Johnson 25 hp "slipping"

Check the prop by marking the lines as suggested.<br /><br />The pin can be bent by the prop slipping and catching under high load.

 

[G DANE]

Re: '77 Johnson 25 hp "slipping"

The 77 25 HP's had no shear pin, they had splined shaft from 76 and on. However both the 71 - 75 and the later propellers has a rubber bushing. The brass hub on older propellers hide the rubber. The older ones tend to slip only by age. A propshop can rehub it. If the shearpin does not catch the groove in hub, someone probably forgot to line it up with the groove when putting propeller on. A too large pin that wont fit in groove cant pass thru hole on propshaft.

 

[G DANE]

Re: '77 Johnson 25 hp "slipping"

Just got a thought ? Does your prop hub have a groove like a wood screw ( not phillips ) to receive the shear pin ? If someone put a propeller from a 1977 motor on yours, which is an older motor, the prop will be for splined shaft, not for shear pin, and as soon as prop meets resistance in water it will spin on shaft.