keeps shearing the shearpin

[ryano79]

I have a 74 evinrude 25 hp it runs fine idles well and goes into gear at low idle fine. But when I go to plane out right as the boat levels off it shears the shearpin every time. So I got tired of it and got a shaft of a screw driver and cut the same length as a shearpin it worked, although it would do the same thing when I take off but it wouldn't shear the screwdriver it would just feel like I hit something every time i take off from idle. Now it has broke the screwdriver shaft. I cannot find another case like this in the forums, your help would be appreciated.

 

[bktheking]

Re: keeps shearing the shearpin

Have you tried the correct "drive pin" , the one that OMC sells. Soft material will shear, sounds to me that's what is happening- shear pins will do exactly that, shear.

 

[Rick.]

Re: keeps shearing the shearpin

This is a new one to me. Does your prop turn freely in neutral? Best of luck. Rick.

 

[Haffiman]

Re: keeps shearing the shearpin

When shear pins breaks like this it is normally caused by:
Worn prop-shaft hole, too big for the pin.
Damaged bushing in the prop and the pin does not longer fit properly.

 

[F_R]

Re: keeps shearing the shearpin

Pure and simple, for some reason it is jumping out of gear, turning one half of a rotation, and instantly slamming back into gear. The jolt is what is breaking the pin. It is the classic symptom of a worn out clutch dog and forward gear OR loose, mis-adjusted shift linkage. Bad clutch dog will destroy the linkage and loose linkage will destroy the clutch dog. You have to look at the big picture. Normally, it will continue to jump/slam while under way and just get worse and more expensive to fix every time it slams.

The 1974 has detents to help hold it in gear, but they can only do so much. Beyond that, it will still jump.

 

[Silver Heels]

Re: keeps shearing the shearpin

The "shear pin" on your motor is not supposed to shear. Years ago, the drive pins used to be made out of brass and designed to shear if the prop hits something hard. Guys were leaning over the back of their boat attempting to pull the prop and replace that pin. After enough guys fell overboard the industry went to a design where the hub in the prop on the old pin drives can give, but the "shear pin" stays in tact. At least thats how my friendly neighborhood outboard guru put it.

 

[ezeke]

Re: keeps shearing the shearpin

The problem is most likely to be the result of a loose propeller as covered in the attached service bulletin #1290.

The propeller hub would continue to slam the drive pin until it breaks, or the hub of the propeller would be damaged beyond repair.

Some aftermarket props cannot be tightened enough without adding shims; some nylon washers may provide enough additional length.

 

[boobie]

Re: keeps shearing the shearpin

Agree with FR above. He just saved me some typing. LOL.