Flywheel Woodruff Key Curiosity Question....

[jbuote]

I've recently read posts about folks replacing flywheel keys, and I've replaced mine as well.
​Each and every time, I've seen that you should NEVER use hardware store type keys as they won't hold up..

​To be CLEAR... I agree wholeheartedly that original factory parts should be used. I use only factory or third party direct factory replacement parts. Just like the factory key I bought for my Johnson..

​The curiosity question then, is this...

​The taper of the crankshaft and the flywheel is really what holds it together. It's a press fit when properly torqued.
​The taper acts as a lever holding the flywheel in place. (when properly torqued).
​The real purpose of the woodruff key as I understand it, is to properly align the flywheel on the crankshaft during installation. Then once it's torqued down, then the taper press fit holds it in place.

​So why does the strength of the woodruff key matter at that point?
​It's been a LOOONG time since I've worked as a mechanic in auto or learned about Aircraft maintenance, so I'm SURE there's something I'm missing and/or forgot.

Anyone care to refresh my memory, or enlighten me?
​I love learning/re-learning information!!

Thanks!!

 

[Fed]

The wrong key or incorrectly fitted key may not allow the flywheel to go on far enough to fully seat around the complete surface of the taper.

 

[Scott Danforth]

a good quality woodruff key is made to the ANSI B17.2 1967 (also ISO 3912 - 1977) standard to make them interchangeable. woodruff key numbers indicate their dimensions with the last two numbers being the diameter in eights of an inch and the preceeding number being the width in 32nd of an inch OMC bought them from the lowest cost source that met the standard. some where stanho, some were standard steel, some were wilson

since the key is made to a standard, short of buying from bob's discount china made hardware, you would be fine

 

[Bonaventure]

OK, so is there a chart that can give us the size key that we need without removing the flywheel? I have a 2 hp Johnson.

 

[racerone]

It is NOT the strength of the material !!--It is NOT a standard size woodruff key.------Look this up yourself.-----For some years OMC used the same part # key for all motors from 9.9 to 300 hp.----That would indicate to me that the key is used to locate the flywheel for proper timing !!

 

[F_R]

The 2hp uses the same 120395 key as a bazillion other small OMC motors. It is a metric key (4mm). I just tossed a caliper on a few and they averaged .156 thick x .607 long x .237 high. The .237 one has a flattened bottom. Others do not have the flat and came up .253 high.

I'd say much of the confusion arises over the fact that it is a metric key.

Wondering, why would anybody search for a hardware store key when the 120395 is laying around in every outboard mechanics' junk drawer?

 

[Scott Danforth]

standard 505 (5/32 x 5/8) key is .156 thick. .602-.612 long and .234-.250 tall (depending on depth of flat)

 

[F_R]

standard 505 (5/32 x 5/8) key is .156 thick. .602-.612 long and .234-.250 tall (depending on depth of flat)

Did not know that. Thanks

 

[Scott Danforth]

here is the chart with min/max dimensions

http://www.engineersedge.com/woodruff_keys.htm

 

[Scott Danforth]

here is the DIN 6888 metric charts

http://fullerfasteners.com/products/din-6888-woodruff-key/

 

[Bonaventure]

Thanks for the quick response. I was under the impression that it was a non standard Key.

 

[jbuote]

Wow, Thanks!
​Lot's of great info here..

​I appreciate the reminder on this!!

​You folks are the best!

Joe

 

[Driftwood Jim]

woodruff keys-
1-used to line up parts
​2- used to protect parts in case of catastrophic failure such as a bad back fire which would want to turn the motor backwards, bearing failure causing driveshaft lock up among other reasons that cause things go ballistic
they are for protection, the flywheel stores alot of energy
example your lawn mower- you run over a branch or something the key shears off protecting the motor from damage