1973 18 hp evinrude flywheel key shearing

scuba_redneck

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Hey guys, my 18 keeps shearing flywheel keys and I am absolutely stumped on why. They key passages do not appear worn and the engine runs fine with a good key in until it shears. Does anyone have any ideas on what would cause this?
 

Will Bark

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Re: 1973 18 hp evinrude flywheel key shearing

Are these OMC keys or ones from hardware store? OMC keys shouldn;t shear if they are torqued correctly. I am not at home right now so someone else will have to chime in with the correct torque.
 

kbait

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Nov 13, 2007
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Re: 1973 18 hp evinrude flywheel key shearing

If torqued correctly, the flywheel wouldn't move on the shaft if the key wasn't even there.. It's actually a guide to line everything up perfect.. once torqued, there should never be any movement between the tapered shaft and flywheel.
 

boobie

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Re: 1973 18 hp evinrude flywheel key shearing

Flywheel torque. 40-45 ft lbs.
 

F_R

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Re: 1973 18 hp evinrude flywheel key shearing

Flywheel and shaft tapers must be in near perfect condition, rust free, and very clean and dry. Then you must torque the nut to 40-45 foot pounds.

I should add that every time the key shears, it causes some damage to the keyways and tapers. Keep it up and you will have a junk motor on your hands. Do it right the first time and that won't happen.
 

reiddo1

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Re: 1973 18 hp evinrude flywheel key shearing

With the risk of extreme repudiation, I was told to use a medium strength thread locker on the tapered faces and clamp down to the specified torque. This certainly solved my problem on an old 79 Evinrude 200 hp. Good luck.
 

Faztbullet

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Re: 1973 18 hp evinrude flywheel key shearing

Lap the flywheel to the crank, tighten to correct torque and your problems will cease....
 

boobie

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Re: 1973 18 hp evinrude flywheel key shearing

Do what was said above along with using the correct OMC woodruff key.
 

Tim Frank

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Re: 1973 18 hp evinrude flywheel key shearing

With the risk of extreme repudiation, I was told to use a medium strength thread locker on the tapered faces and clamp down to the specified torque. This certainly solved my problem on an old 79 Evinrude 200 hp. Good luck.

That's why there is a recurring theme in here..."Get an OEM manual"; that way you aren't at the mercy of someone who may have good intention but does not have a clue. :)
That advice put your motor at risk.... and have you had the flywheel off since?
 

reiddo1

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Re: 1973 18 hp evinrude flywheel key shearing

That's why there is a recurring theme in here..."Get an OEM manual"; that way you aren't at the mercy of someone who may have good intention but does not have a clue. :)
That advice put your motor at risk.... and have you had the flywheel off since?
Yes I did take it off to make certain that it had not moved or sheared; that was before I filed an index mark across the crankshaft and flywheel. Medium strength locktite on the tapered shaft did not prevent me for getting the flywheel off with a puller.
 

EddiePetty

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Re: 1973 18 hp evinrude flywheel key shearing

Tapered fits, as in your flywheel-to-crankshaft, should be assembled DRY. Anything between the tapers will result in a loose fit as exemplified by the easy removal of the flywheel after using Locktite.
 

Grub54891

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Re: 1973 18 hp evinrude flywheel key shearing

Tapered fits, as in your flywheel-to-crankshaft, should be assembled DRY. Anything between the tapers will result in a loose fit as exemplified by the easy removal of the flywheel after using Locktite.

Yup dry installation, as stated already, lap the wheel to the shaft,make shure it's clean and torque to spec's. had one come on the shop that had that same issue,the owner had put a dab of grease on the shaft and it kept shearing the key. Also it had arked electrically between the flywheel and shaft, causing some pitting. I lapped the flywheel,and also found a bad regulator in the thing.problem solved!
 

scuba_redneck

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Re: 1973 18 hp evinrude flywheel key shearing

Well guys as always you have been very helpful. I have been running hardware store woodruff keys after the factory key sheared. I've split two hardware store keys and the factory one. I reckon I'm going to have to bite the bullet and order an omc key. As far as my flywheel and crankshaft, I always clean with acetone and torque to spec when I'm finished. I just didn't know if the key shearing was a symptom of a bigger problem that y'all knew of.
 

scuba_redneck

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Re: 1973 18 hp evinrude flywheel key shearing

I can always tell when the key pops by when the motor begins running rough and not wanting to idle or open up to wot
 

HighTrim

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Re: 1973 18 hp evinrude flywheel key shearing

Its hard to say why the original key broke now.

But can most definately say that they are continually breaking due to using the hardware store keys as everyone stated. Common on here to hear of guys trying hardware store keys, also as common to hear them come back saying the key sheared.

Also to note, please do not put any Loctite on the taper, there always seems to be one guy that has a neighbour that told him to try Loctite. I spent 3 days once trying to get a flywheel off that someone put Red Loctite on!
 

F_R

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Re: 1973 18 hp evinrude flywheel key shearing

I have had to actually cut them off when some genius Loctited it on.
 

scuba_redneck

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Re: 1973 18 hp evinrude flywheel key shearing

The loctite was never even considered from previous research. Are the omc keys hardened above the hardware store keys or are they a different metal altogether? I will be ordering a new omc key soon to hopefully end the issue. Everything else on the engine is rock solid thanks to all the help from you guys. Now if I can just keep a key in it to keep the timing right. I think the original key, being almost 40 years old, might have just been old and ready to retire
 

Lone Duck

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Re: 1973 18 hp evinrude flywheel key shearing

Well guys as always you have been very helpful. I have been running hardware store woodruff keys after the factory key sheared. I've split two hardware store keys and the factory one. I reckon I'm going to have to bite the bullet and order an omc key. As far as my flywheel and crankshaft, I always clean with acetone and torque to spec when I'm finished. I just didn't know if the key shearing was a symptom of a bigger problem that y'all knew of.
Another very rare happening I have seen on small engines is that if the engine is slightly to far advanced , and the flywheel fit is not tight enough the stress of firing against the force of the flywheel revolution will in time shear the key. Or if the wheel is out of balance. I know ,I know it's a very long shot. But stranger things have happend
 

Will Bark

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Re: 1973 18 hp evinrude flywheel key shearing

If you have a NAPA store in Amory they may have them(OMC) in stock as the do here in Hattiesburg.
 

steelespike

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Re: 1973 18 hp evinrude flywheel key shearing

If the Key is just to position the flywheel and the proper torque keeps the flywheel in place why is the OMC key
supposed to be the key(no pun intended)to success.
 
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