Hit a Log this Morning

[drifter]

Well, with all of the rains we’ve had in central Texas it was bound to happen. Our Lake Georgetown is up 21′ in two weeks and the debris is way heavier than I thought.
Went out this morning in my 63 Sea King with a 1957 Johnson 7.5. Was cruising along when WHAM! – hit a submerged log.
The engine revved way up and the boat did not move.
Sheared the pin I thought. But then, as I throttled down, the boat began to move. As long as I held it at about 1/4 throttle, she’d move along fine, but when I throttled up, she would just rev up and not move.
I made it back to the dock – puzzled all the way.
Got home, put the little Johnson on the workbench mount and checked the shear pin. 100% intact.
So, started the tear down thinking it has to be the shock absorber. Well, the shock looks fine internally. It measures 6 23/32". Spring looks good as far as I can tell.
I pulled all the gears and found everything in order.
Now to my question(s). Can the shock "go bad" and simply slip under load? Is there something I’m missing in the drive line?
I have a spare shock and will install it this afternoon. I sure am puzzled.
Thanks for the help.
Nick

[ggoldy]

Spun prop?

[drifter]

I don’t think so as the prop hub is a solid cast piece and the shear pin passes through this solid cast hub.

[bobprock4200]

Drifter, I think you are correct in your assumption the shock absorber is at fault. I think at low speeds there’s enough tension on that spring to provide enough friction to drive the prop slowly, then as you speed up it start slipping. Better than busted gears though. A similar issue drove me crazy ’til I figured it out.

[Doug Wilson]

sounds like the hub in the prop got spun, may not look like there is a hub that can spin but there
is. Spun the hub on my 58 10hp last fall, cost @45 to get it fixed at a local prop repair shop.
Doug

Doug

how is it motors multiply when the garage lights get
turned off?

[drifter]

I just do not see any way the hub can spin. The prop by all appearances is cast as one piece. The shear pin passes through the cast hub at the rear of the prop directly in front of the cotter pin. The hub, shear pin, and cotter pin is then covered by the rubber end cap. Maybe my old eyes are deceiving me, but it sure looks like that prop is one piece.

[dave-bernard]

mark the shear pin and the outer prop for reference I use permanent magic markers.and run and slip again . now check your reference points.

[Doug Wilson]

might also take a good look at the blades maybe bent enough that it is causing the issue

Doug

how is it motors multiply when the garage lights get
turned off?

[outboard315]

I can picture the prop, it is a aluminum prop with the shear pin slot casted into the back. I wonder if it is something in the lower unit.

[Mumbles]

quote Drifter:

I don’t think so as the prop hub is a solid cast piece and the shear pin passes through this solid cast hub.

You are correct Drifter and your prop is solid with no rubber hub in it.

I would strongly suspect the shock absorber is slipping. If you mount it in a vice and grab the other end with a pipe wrench, you can see how much torque is needed before it slips. 6 11/16 is a good measurement.

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