Flywheel key keeps shearing

[89retta]

I have a 77 Evinrude 140hp and i've sheared the key for the third time.Any ideas as to whats causing this.The crank does have some surface rust on it should i use some emery cloth to clean it up.

 

[Monte1961]

Re: Flywheel key keeps shearing

Are you using a OEM key or one from the local hardware store!? Hardware stores won't work. And if you are using OEM, are you torquing the crank nut down to spects? Post back? Post back results.

 

[Faztbullet]

Re: Flywheel key keeps shearing

You need to lap the flywheel to crank, this is stated in the earlier service manuals. Just remove key and apply valve lapping compound to the crank. Slide the flywheel on and spin the flywheel over the lapping compound. Start with the coarse compound and move to the fine compound. When finished, thoroughly clean all of the compound off of flywheel, keyway and crank.

 

[89retta]

Re: Flywheel key keeps shearing

OEM key but did not torque it down.Do you know what the torque spec is?

 

[levi_tsk]

Re: Flywheel key keeps shearing

105 ft pounds

 

[Silvertip]

Re: Flywheel key keeps shearing

Examine the slot in the crankshaft as well as in the flywheel. If the slots have been worn by previous shears, it will only get worse. The key must fit snuggly in both the crank and flywheel.

 

[boobie]

Re: Flywheel key keeps shearing

The key doesn't hold the flywheel on. It's only there for proper timing position. You have what is called a "morse taper" between the flywheel and the crankshaft. Both surfaces on the c/s and f/w have to be clean and shiney, dirt and oil free. Then the f/w has to be torqued properly. As Faztbullet suggested, the lapping is a good idea. When you install the oem flywheel key it's outer edge has to be parallel with the center line of the c/s.

 

[levi_tsk]

Re: Flywheel key keeps shearing

agreeed what boobie said is THE most important part the key MUST have the flat side parallel to the CL of the crank and it will shear EVERYTIME if you have it follow the taper

 

[jimbo_jwc]

Re: Flywheel key keeps shearing

Key must be correct grade steel hardness to shear with good tight fit in woodriff on crank and flywheal no oil what so ever torq to mfg spec and see what happens . use permanet marker or blueing to see if taper is matched

 

[jimbo_jwc]

Re: Flywheel key keeps shearing

Key must be correct grade steel hardness to shear with good tight fit in woodriff on crank and flywheal no oil what so ever torq to mfg spec and see what happens . use permanet marker or blueing to see if taper is matched

Fatzbullit has correct mateing procedure he might have hand sraped ways in younger days