flywheel key

Booner

Petty Officer 1st Class
Joined
Feb 15, 2005
Messages
276
I have a 1957 18 hp Johnson that will shear a key at least once a year. Is this normal ? <br /> Thanks
 

cajun555

Chief Petty Officer
Joined
Dec 20, 2003
Messages
483
Re: flywheel key

No. Need to make sure the flywheel is free of oil and greese as well as the crank. Torqe fly wheelnut to specs. Don't have specs right in front of me at the moment. Might have to use a lapping compound on flywheel and crank for a better fit of the 2 pieces. Make sure motor is tuned properly. If your motor backfires and nut is not tightened to specks it can cause a stripped key. The keyway is a weak link just like the sheer pin.<br /><br />Just looked up torqe of F/W nut-- 480 to 540 in/lbs.
 

Booner

Petty Officer 1st Class
Joined
Feb 15, 2005
Messages
276
Re: flywheel key

Thanks cajun555 will do but what is a lapping compound ?
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: flywheel key

Be very careful with the lapping compound. Its a valve grinding type compound that you put on the tapered part of the crank and then put the flywheel on without a key. Then you turn it back and forth to "seat" it in. The process removes metal from the taper and the flywheel.<br /><br />I've seen guys do it so much that the flywheel no longer is an interference fit to the crank taper but rests on the shoulder below the taper. <br /><br />The two tapers are supposed to be an interference fit. Just be careful. Also make sure the bottom of the nut is flat. No burrs. <br /><br />A good nut, the right key (make sure you havent been using the wrong one accidentily) and the correct torque is the trick. Remember, all the key does it position the flywheel. The tapered fit is what holds it. If it gets loose for any reason the key will shear.
 
Top