flywheel key keeps shearing changed 5 times

stevemcmain

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Nov 7, 2009
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I have a 1970 18 hp evinrude. I put new coils condensers and points and plugs has spark and fuel will start but only runs for 20 seconds and then key breaks and motor kills. i have no idea what is breaking the keys please help
 

tashasdaddy

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Re: flywheel key keeps shearing changed 5 times

not torquing down the flywheel nut. i believe it is 70 ft lbs. but look it up.
 

Cofe

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Re: flywheel key keeps shearing changed 5 times

The key must be installed with the straight edge perfectly vertical with the engine's driveshaft, crankshaft, etc, not aligned with the crankshaft taper, and the flywheel must be properly torqued. There should be a notch in the key that must go up. The round part of the key goes in the crankshaft.
Also..... after once shearing a key, the crankshaft and flywheel tapers must be cleaned up, get rid of the burrs, etc. If the flywheel can't set properly on the crankshaft taper it will loosen up and shear again.
To torque, one needs the proper torque wrench and socket, and also a strap wrench so as to hold onto the flywheel. Hope this helps you.
 

lindy46

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Re: flywheel key keeps shearing changed 5 times

Torque that flywheel nut to 40-45 ft. lbs.
 

F_R

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Re: flywheel key keeps shearing changed 5 times

The key must be installed with the straight edge perfectly vertical with the engine's driveshaft, crankshaft, etc, not aligned with the crankshaft taper, and the flywheel must be properly torqued. There should be a notch in the key that must go up. The round part of the key goes in the crankshaft.
Also..... after once shearing a key, the crankshaft and flywheel tapers must be cleaned up, get rid of the burrs, etc. If the flywheel can't set properly on the crankshaft taper it will loosen up and shear again.
To torque, one needs the proper torque wrench and socket, and also a strap wrench so as to hold onto the flywheel. Hope this helps you.

The notch goes down!! It is merely to take the slop outof the cam.

As said, once you shear the first one it causes damage. Shear the second one and it causes more damage, The third----etc. SO, check the tapers. They must be virtually perfect. The key slots must not be battered. If everything is still serviceable, proceed--

1. Crank and flywheel tapers must be shiny clean and smooth.
2. Tapers must be completely dry
3. You MUST use a torque wrench to tighten the nut to 40-45 ft/lbs.

Of course, if the crank and flyweel are damaged, you have a parts motor.
 

Cofe

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Re: flywheel key keeps shearing changed 5 times

The notch goes down!! It is merely to take the slop outof the cam.

In my manual for my 25hp it says the notch goes up.....but if FR says it goes down, it must go down. I trust his judgment over my cheepo manual.
 

Faztbullet

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Mar 2, 2008
Messages
15,589
Re: flywheel key keeps shearing changed 5 times

Remove the keyway and take some valve lapping compound and lap the flywheel to crank taper so it has maxium contact,clean it up and reinstall using F_R suggestions.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: flywheel key keeps shearing changed 5 times

The notch goes down!! It is merely to take the slop outof the cam.

In my manual for my 25hp it says the notch goes up.....but if FR says it goes down, it must go down. I trust his judgment over my cheepo manual.



And the factory manual sez----
 

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