1972 Johnson 20 hp - Pin sheared or worn dog?

[Simpleton52]

Just got this motor, took it out on my 14' V-hull.
It ran just fine away from the dock at lower speeds. Opened it to WOT and after a few seconds (mayb 15) it acted like it jumped out of drive. It instantly rev'd way up, I lost forward thrust. I let off the throttle, rolled it back in, and had forward power again.
It ran for two hours just fine at 1/2 throttle.
I have two different mechanics tell me two completely different things. One says that's a classic sheared prop pin.
The other tells me the whole lower unit has to be rebuilt.
Any way to easily tell which it is?

Thanks!

[lindy46]

If you had a sheared pin or spun hub you probably wouldn't be going anywhere. If it jumps out of gear at high speed, it's most likely the clutch dog/forward gear which are worn.

[Blade_Link]

sounds like the clutchdog is worn, the lower end needs to be rebuilt, seals are probably worn as well you are going to need to rebiuld the lower end, not a bad job, but a bit of a pain, if the prop pin sheard you would have no thrust at all, the prop would no spin at all.

[Sea18Horse]

My money's on a slipping prop hub. In either case you need to find out which it is. First step is to remove the prop and scribe a line across the end of the prop and hub. Then take it out, make it slip, then take the prop back off and see if the scribe marks are still aligned.

On a worn clutch dog, if that paricular lower unit has the detent up by the shift lever it would pop out of gear momentarily and then pop back in. It would feel like you hit a log. If it has the detent down inside the lu then it would just pop out of gear and stay there. You would have to shift it back in. It doesn't sound like either of those is the case. Good luck!

Cheers.....................Todd

[Vic.S]

If its a sheared pin you'll not get any drive forward or astern and youll be able to take the prop off find the broken pin and renew it.

If its a spun prop it'll drive at low powers but not at high power.

If its the clutch dog it will jump out of gear into neutral and you will have to put it back into gear to restore drive. You may be able to hold it in gear.