1986 Johnson 120 VRO

[Whalermon]

I was cruising down the river last month when I heard something like the lower end of the engine hit something in the water. The boat slowed and I throttled up and the RPM increased and the engine sounded fine, however the boat would not go over 5 +/- knots. I limped back almost 10 miles to the launch at 5 knots. I figured I spun the prop by hitting a submerged log or something because a broken prop shaft or sheared worm drive gear would have disabled the boat completely.

I brought the prop to my local prop shop to have a new doughnut installed and they told me they tested the prop, it wasn't spun and that it was fine. I reinstalled the prop and launched the boat, the engine runs and revs fine but the boat will not exceed 5 knots.

Has anyone experienced this?

[boats.net]

Have you looked at bottom of boat to see if have damage to hull? Doesn't sound like a gear or bearing problem in lower unit but might check lower unit oil for metal in oil. The bottom drain screw has a magnet on it and you see a lot of metal on screw( small amount of metal is normal) then may have damage inside lower unit.

[Whalermon]

I drained the gearcase this morning. The gear oil was clean with no signs of water intrusion and no metal, not even filings. I am going to take the prop to another shop to re-test the hub, I think its a simple spun hub.

[boats.net]

You can scribe a line across the hub of prop and down across prop washer & nut. Take boat out for a run and if your line is still lined up then prop hub is not slipping. The prop hub does normally need replacing after hitting something.

[Whalermon]

I would have it in the water today if there wasn't 4" of ice on the river. Is there any other way of testing for a spun prop other than taking it to a prop shop?

[boats.net]

Not unless you have an old prop shaft you can clamp into a vise slide prop over shaft and try to turn prop blades on hub to see if slips.