flywheel / crackshaft KEYS Snap over and over again

All right heres a good one.. i just replaced my stator on my 1995 mercury force 120. i noticed the key for the crackshaft was a little wornout but replaced it anyway for the testing of the stator. Low and behold it snapped! So after visiting 2 west marines, 3 auto parts stores, and a tractor supply company i had purchased about a dozen diffrent keys to see which would be the best fit.. i got three to meet the match and all 3 snapped.. i wounder if its because the metal isnt strong enough? (the flywheel was tightened properly).. i just dont get it? or where i can get the proper key.. Any suggestions?

Thanks for lookin

Re: flywheel / crackshaft KEYS Snap over and over again

To shear the crankshaft key the flywheel must move on the crank.

That usually means that the flywheel wasn't torqued correctly, but you have done that. . . haven't you? What torque did you use?

Another common cause is an imperfect fit of the flywheel taper to the crankshaft taper caused by damage to one or the other. You said the old key was worn. Did it damage the slot in the crankshaft?

Finally, bad ignition timing (too far advanced), particularly at low speed, can shear the key. Is your new stator correctly installed?

Good luck, and let us know what you find.

Re: flywheel / crackshaft KEYS Snap over and over again

Well the repalcement keys were not what i would call a "perfect" fit, but very close. the crankshaft slot is fine with the exeption of a broken key in it lol.. it can be removed i just called it a day.

the stator is in properly but being that the motor is a 95 force 120 the stator is obsolete, so i have to rely on used.. the one i got looks idendical to the old in all aspects with the exception of an additional groung wire(that was NOt hooked up during testing). but she fired up and ran.. idled good until it snapped.

i did order factor keys today, but i just dont get it? i dont think the timing is off but hard to tell.

Do you happen to know the correct amount of torque for the flywheel? perhaps im wrong and it wasnt enough.

Re: flywheel / crackshaft KEYS Snap over and over again

Correct flywheel nut torque is 95 FOOT pounds. Do not use keys that "almost" fit or "look correct." It is a standard key and you should be able to get aftermarket correctly fitting ones. An incorrect key will allow you to set the flywheel on slightly off and timing will differ. Anyway, after replacing a flywheel you should check timing as a matter of course.

Now: Before re-installing the flywheel, you should check the contact patch of the taper. Nothing less than 80% is acceptable. Clean the crankshaft taper and draw a number of vertical lines on it with a pencil or other marker. Put on the flywheel without the key and spin it on the shaft. Remove it and check the lines for rub-off.

If less than 80% (90 is better in my opinion) then use a little fine lapping compound or abrasive sink cleaner mixed in oil and lap the shaft and flywheel together. Clean everything well and assemble. Be careful: Lapping to much or too many times will cause the flywheel to bottom out on the land at the bottom of the taper. Then, it will always break keys and the only cure is a new flywheel and crank---expensive!

Re: flywheel / crackshaft KEYS Snap over and over again

so i want at least 80% of the lines to rub off?

Re: flywheel / crackshaft KEYS Snap over and over again

Capt.Brettski said:

the stator is in properly but being that the motor is a 95 force 120 the stator is obsolete, so i have to rely on used.. the one i got looks idendical to the old in all aspects

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You do know that several aftermarket companies make replacement stators for your motor....most well known is CDI. So you don't have to depend on used.

You also should pay attention to what the part number was on your original stator. Mercury did a running upgrade during '91-'95 model years.....the old style stator was a 9A part, the new was a 16A part. And the 9A stator used a rectifier that is not compatible with the 16A stator. Just FYI.......

Re: flywheel / crackshaft KEYS Snap over and over again

Yeah, you want at lease 80% of the lines rubbed off.

Re: flywheel / crackshaft KEYS Snap over and over again

Try to lapp the taper and torque to correct value, if it doesnt work use Loctite lockingfluide on the taper. I have done that on a Chrysler 60Hp with MagII ign. Had the same problem, lapping and torqueing to right value did not work. Then I used Loctite and that solved the problem.

Re: flywheel / crackshaft KEYS Snap over and over again

Nordin said:

Try to lapp the taper and torque to correct value, if it doesnt work use Loctite lockingfluide on the taper. I have done that on a Chrysler 60Hp with MagII ign. Had the same problem, lapping and torqueing to right value did not work. Then I used Loctite and that solved the problem.

Click to expand...

Good heavens, will you be able to ever remove the flywheel when the time comes? I think it's better to ensure the taper is clean and true, and use the correct size key.

Re: flywheel / crackshaft KEYS Snap over and over again

No problem to remove, the taper is for the flywheel not to turn on the crankshaft, the Loctite too. When you remove the flywheel you pull it from the taper. My experience is that there is no problem to remove the wheel after you used Loctite. Of course lapp and use the right key, right torque first.