Breaking Shear Pins

[shooter_mcgavin]

Hey all. I have a 16-horse spirit outboard motor (about 30 years old) that keeps breaking the shear pin in the prop. It seems to happen when I hit bigger waves. Its weird because I will be in deep water bouncing across the lake and the pin will break. Before anyone asks, I am careful to keep the prop from hitting the bottom! Anyone have any experience with this issue? Thanks!

[CAMAN]

If you're using the correct shear pin, the next thing I would look at is the pitch of the prop. Too much pitch will cause excess torque on the shaft.

[hydro]

If you keep breaking the pin for no apparent reason, check two things. First, look at the groove in the prop hub and check for burrs or excessive wear, second, look at the hole in the prop shaft for out of round or elongation at the edges. Both of these things cab break pins without hitting obstructions. If is the prop, replace the hub or the prop. If it is the shaft you may need to get it replaced.

[shooter_mcgavin]

Thanks for the ideas guys, I'll take a closer look this week. Trying to diagnose the problem might be smarter than my other idea of finding a steel bolt that fits instead. Just sick of breaking shear pins!

[Ufatz]

Hey shoot, are you familiar with the term "cavitation"? If not, look it up and understand what it is and how it happens and what its effects can be.

I believe the boys may be right on though with the distorted hole for the pin or a prop problem.

[Tom7227]

Just guessing but are there different diameter shear pins or ones that have different breaking points? I would think that back when all motors used them there had to be a variety. One for a 3 horse wouldn't do for a 30. Maybe you have the wrong pins?

[shooter_mcgavin]

I purchased the boat used this year, and the owner gave me extra shear pins (good thing). They seemed to fit well. When I ran out of those, I got some more at a boat dealer that were slightly different, and broke those as well. I'm taking my last shear pin and the prop in to the dealer today. Hopefully they can tell me if the prop is correct for the motor.

The hole for the shear pin looks good on one side, but is slightly distorted on the other side.

Thanks for the help guys.

[Surface Tension]

Along with worn grove, wrong prop, or wrong shear pin I'll throw in sloppy fitting prop, or tightening the prop nut down to much.

Finger tight then use a wrench 1/8-1/4 turn to line up the holes in the shaft and prop nut for cotter pin.

[shooter_mcgavin]

Lots of good ideas here. Funny, I called three different mechanics yesterday and all seemed stumped. Two of the mechanics said they would just use some tempered steel instead of a shear pin and call it good.

I met one of the mechanics and showed him the prop. He seemed to think it was original to the motor because it said "made in Japan" (interesting side note, the motor was made by Arctic Cat). He thought I could get a new prop for about $150 if I wanted to trouble shoot, but he though the prop looked good enough, with the pin fitting correctly. To me, the prop seems oversized for the motor, but I'm no mechanic. The boat does seem slow to plane out, with a surprising top speed. Is this what an oversized prop would do?

[CAMAN]

That's what a prop with too much pitch would do.

[Ufatz]

Puzzled by mechanics telling you to use something made of "tempered steel" instead of the soft metal of a shear pin. Does somebody not understand the purpose and intent of a shear pin. Does the word "shear" give you a clue. What is the potential result of "no shear" when the prop hits a solid object......like an old off brand motor somebody has dumped in the lake.

[shooter_mcgavin]

I'm surprised too Ufatz. I just got off the phone with a mechanic at Twin City Outboard. Not only did he tell me to just put a bolt in there because he won't be able to replicate the problem in his shop, but he also said he can't repair the engine stop button in the tiller (the kill button is a new problem I'm having).

Dan's Southside said they can look at it in a few weeks, but didn't sound enthusiastic about their ability to fix it.

Guess I'll rig it! I am going to check at Fleet Farm to see if they have a different shear pin that might be somewhat tougher. As for the engine stop button, I have no idea there.

[Ufatz]

I'll be honest with ya. I fear what you have is an engine that will continue to be a source of mental and fiscal pain. You may have trouble finding parts. Clearly something is not right with the shear pin situation and now the stop switch (which is probably a simple fix) but you might want to sit down and think about coming up with another engine.

I think you said it is a Spirit? engine. No ourboard expert but I have never heard of such an engine. Who made it. And why?....ha ha ha.

Not pickin' on ya.....but might be someting to consider.

Oh! Now I get it.....Spirit is the name of a MODEL of Suzuki outboards. Depending on year you should be able to get parts and advice from Suzuki. They make very solid and dependable motors....have owned several.

[shooter_mcgavin]

Thanks again for the advice all. I found a rubber washer and put that on before screwing on the prop nut, and that seemed to tighten things up. I think the problem was too much play in the prop.

Unfortunately, the motor quit while testing it out. I was running wide open, when the motor started acting like it was running with the choke all the way on. It just slowed down until I let off the throttle and it quit. It smelled like it was flooded, so I'm assuming there's a carburetor issue.

Time to bite the bullet and take it to the shop.