Shear Pin Keeps Breaking

[durk187]

I have a 1968 Evinrude Fastwin 18hp. Its a beauty and runs great. One problem I keep having is that I continualy break shear pins. I have the correct ones installed for the motor. I hit little logs in the water at little more then idle speed and one breaks. Just seems very delicate. I understand that if I hit something that would cause damage it is doing whats its suppose to however I have trouble thinking small obstructions at slow speeds pose a problem. If so and it is functioning correctly it seems like a big pain in the a** and they should've came up with a better system sooner. <br /><br />I have also read that if the prop has a lot of play in it "mine has a 1/2 turn" the prop can load up on a stick and when it frees the richot action is what breaks the pins. <br /><br />I am a duck hunter and always in flooded timber.

 

[ob]

Re: Shear Pin Keeps Breaking

Had the same problem with little 5.5 eska some years back. they do seem to over kill on some of these shear pin composit materials . In my case I changed from aluminum to brass.say from brass to nickel and so on.I'd wager you could probably even use galvanized steel with no wider than most of the pins are,especially when you're motoring easy at low r's.

 

[naughtybynature]

Re: Shear Pin Keeps Breaking

is the pin not just doing it's job. seems like you are hitting alot of debris with your set up. i beleive that even at idle speed your motor has plenty of torque when in gear. personally i'd rather have the pin breaking then having the shock loaded into the gears and shaft. not sure an outboard was designed to be hitting so much underwater debris. have you considered some kind of guard or cage?

 

[durk187]

Re: Shear Pin Keeps Breaking

Ive looked into guards and such. Noithing found for that engine. <br /><br />Its not like im trying to use the motor like a go-devil. The pins just snap with the smallest of obstruction. Sometimes I cant even tell I hit something.<br /><br />I have a buddy that has a 25hp merc, no shear pin but he can run over trees without missing a beat. <br /><br />Just seams like somethings not right. Plus changing a shear pin per outing on the water is getting old. Im just waiting to drop the prop or hub nut in the water.

 

[sloopy]

Re: Shear Pin Keeps Breaking

what type of motor is it>? and merc must make a good engine if they can run over trees!

 

[butlp]

Re: Shear Pin Keeps Breaking

Read the first post Sloopy! Its a 1968 Evenrude Fastwin 18hp

 

[wilde1j]

Re: Shear Pin Keeps Breaking

The solution is simple ... stop hitting stuff. The shear pin's function is to protect the lower unit and prop from exactly that. If you want to cut logs, get a chain saw.

 

[slow_boat]

Re: Shear Pin Keeps Breaking

Even at 'slow/trolling speeds' the prop hitting a stationary object imparts tremendous stress to *ALL* of the drive train, top to bottom. The prop in your engine should have a rubber shock absorber bushing installed between the brass inner hub & the aluminum prop...perhaps this has failed or is defective...check it out as usually this will 'give' before the pin actually shears. Furthermore, props typically sustain noticable damage *along with* shear pin breakage. Maybe a new prop is in order? As mentioned in other posts, outboard engines are not designed to be chain saws but, in my experience, you should check to see if your prop's rubber hub is functioning properly.<br /><br />Would like to buy a NEW Mercury *JUST* like your freind's...don't want his...it has hit too many stumps!!

 

[naughtybynature]

Re: Shear Pin Keeps Breaking

you could easily fabricate your own guard for your prop. take a look on this site and others for some ideas. if ya can't find one to buy.... make your own!

 

[rolmops]

Re: Shear Pin Keeps Breaking

Hello.<br />The original shearpins for your '68 are made of a soft steel that will still bend a bit.They should not just snap.If your prop play is half a rotation then, that is what you should check out, for that seems to be a lot.<br />Another reason for this sort of thing might be that your propeller inner housing has absolutely no give, where it should slip when you hit something light.Try a different prop and see what happens.<br />Good luck.

 

[durk187]

Re: Shear Pin Keeps Breaking

Tried a new prop already and it has the same results. It was said that the prop should sustain damage before the shere pin breaks. This is not the case with me. Both props are flawless and one is brand new. Im not hiting things hard enough to even nick the prop, but is still busting pins. Does anyone know how much play a prop should have when installed?

 

[Hooty]

Re: Shear Pin Keeps Breaking

I'm thinking either the shear pin hole in the prop or the shaft has gotten enlarged.<br /><br />c/6<br /><br />Hooty

 

[ulysees]

Re: Shear Pin Keeps Breaking

put ducked tape over the shear pin, and get brass pins. goodluck

 

[OBJ]

Re: Shear Pin Keeps Breaking

What kinda idle rpm in gear do ya' suppose it's turning duckcommander? <br /><br />But I think I agree with Hooty on the enlarged hole. Makes the pin float and take more abuse when ya' hit something. Like the other guys suggested, try brass and see how that works.

 

[Xcusme]

Re: Shear Pin Keeps Breaking

Duck,<br />I too, think a look at the prop shaft is in order, here's why. The sudden torque of the prop shaft, when you put it in gear, slams against the shear pin along the shear line. This can cause the pin to start to fracture along the shear line, little by little, weakening the pin. Eventually the pin will shear when put into gear or by hitting a small obstruction.

 

[Chinewalker]

Re: Shear Pin Keeps Breaking

Hi DC,<br /> The "play" you're noting in your prop isn't actually in the prop - it's the propshaft rotating between the cogs on the clutch dog inside the gearcase.<br /> Check the hole in the propshaft for burrs or excessive wear that could cause the pin to shear. Check the slot in the prop for the same.<br /> Try a harder material. I've actually used drill-rod in some applications. In racing we use aircraft rivets. It all depends on what risks you are willing to take with the drivetrain.<br /> Also, are you shifting at the lowest possible speed? Hi-revving neutral drops tend to shorten the life span of shear pins and clutch dogs...<br /> Another thought - how tight are you torquing down on the prop nut? It should be snug, but not wrenched down enough to pre-load the pin too much. I usually snug it by hand, then tighten it enough with a wrench to align the cotter pin holes.<br /> Good luck,<br />- Scott

 

[cobra 3.0]

Re: Shear Pin Keeps Breaking

I had bought a used 18 Merc that liked to bust up props and was 'stump sensitive'. It was the leg of the motor that was too short and worn out. I had it fixed at a prop shop and it was much better after that. <br /><br />I agree with most of the above fellows. Change to a tougher material for your pins. An old drill bit that fits snug into the shear pin spot should definitely help.

 

[BillP]

Re: Shear Pin Keeps Breaking

I had the same situation happen and used a different brand shear pin to stop the problem. Chances are yours are crappy aluminum alloy. Breath too hard and they break. They were the ones all the marinas had displayed. Original OMC pins are the best. You will have to work hard to trash that OMC 14/15/18hp gearcase.

 

[TXWings]

Re: Shear Pin Keeps Breaking

slow_boat had written <br /><br />"you should check to see if your prop's rubber hub is functioning properly."<br /><br />My 1960 18 hp evinrude doesn't have a rubber hub. Sheered a few pins lately, at idle speed, in this low water, on mine, as well. There is a #8 and #17 pin. The drill bit idea may be the best.