CANT FIND OUT SHEAR PIN SIZE ???

[SAILNOOB]

I have a 5 HP yamaha 1998 short shaft on my only functional tender for my live aboard sailboat. The tender is too big to be rowed. So this is rather important. I rebuilt the carb last week, and after that the motor ran like never before. But then it started revving really high when I would open throttle, but no more thrust would be produced, in fact less. Now it is getting worse, and I think I can only run the engine at lower and lower speeds or it starts screaming, not pushing anything. This screaming does usually stop after about 5-10 seconds and the boat starts moving again, but I can't figure out what is causing it. I figure it could also be a loose gasket somewhere sucking air, but I'm not sure. I figured its worth checking the shear pin, but I can't even find the size of it! I had to buy every single pin from west marine and will just return the ones that don't fit but that is ridiculous! Is there no resource for finding a shear pin size? Why is outboard repair such a mystical discipline? I checked the yamaha repair manual 40 dollars at west marine, and nothing on this. I checked the owners manual and nothing on this. COME ON!!!

 

[jbcurt00]

If the prop spins under load and the boat moves, ts not the shear pin.

Spun hub would be my guess.

Based on a diagram of the lower unit, theres a cotter pin holding the prop nut, but I dont see a shear pin for the prop

 

[Bondo]

Ayuh,.... Welcome Aboard,.... iboats is a Family site, keep that in mind when postin', 'n please read our postin' rules, 'n guidelines,.....

My guess is yer motor don't use a shear pin,... shear pins went away in the '60s,...
A broken shear pin is an all or nothin' kinda thing, so it also doesn't fit yer problem,....

My guess is, yer prop uses a rubber hub, 'n it's sheared, in which case, ya need a new prop,....

Either way, step #1 is to remove the prop from the motor, 'n Look to see what ya got, 'n what's broken,.....

 

[Texasmark]

O.T. Noticed your terminology. That's what we called the brass pieces of rod used to lock the prop onto the shaft. Why did we call them "shear" and not "drive" pins....which is their primary purpose? It's because we expected it to stay intact so that we could "drive" the prop. But, at the most inopportune time it would choose to "shear" and leave you on the windward side of the jetties/rock piles/harms way unable to "drive" your prop and get the !@#$%^&*() out of harm's way. That's why I levt OMC and went to Merc. They had a splined shaft and relied on the rubber hub to slip when an obstruction was hit which would immediately reset upon cutting the throttle and shifting into N for a second and you were back on your way!