Woodruff keys, timing and all that jazz

Let's say, hypothetically, I shear the woodruff key on my '63 Gale (40hp). If that were to happen, how would I go about replacing it with the correct one?
It had been firing up with no problem, but only running on one cylinder. After learning one ignition wire was bad, I replaced it and one coil which was an original part. I was positive I had replaced the key in the correct position having the flat edge straight up and down. I did use a TINY bit of hi-temp black sillicone to hold it in place so I could slide the flywheel back on. I watched over head as I replaced it and saw that I didn't contact it. How can I be sure once I replace the key that I do get it back it perfect position? Is there 0% margin of error?!
And how did it break? The prop was off, lower end sitting in 40 gal. drum of water, and should have had no problem spinning. What happened?

Thanks, as always!

Re: Woodruff keys, timing and all that jazz

Oh, btw, my book tells me to get a special timing fixture OMC
#378966. How important is it to have that to adjust the timing, and how available are those?

Re: Woodruff keys, timing and all that jazz

Be sure mating surfaces of flywheel and crank are clean,free of dirt, grease and burrs.
Outer surface of the flywheel key must be parallel with the centerline of the crankshaft.Thighten nut to 60 to 65 ft lbs.I have a feeling your black silicone may have lubricated things just enough to allow the flywheel to slip.
All those silicone products are pretty slick.you may have to carefully clean the stuff off and be sure nothing
feels slick.I would think if you got the key close to parallel it will work fine.Be sure the keyways are in good shape.
As I understand it the key is to line things up not hold
the flywheel in place so the integrity of the mating surfaces is critical as well as the proper torque.
I'm pretty sure the motor will run fine using the old method of adjusting the points.Just try to be accurate with the placement and adjust carefully to .020.

Re: Woodruff keys, timing and all that jazz

Steelspike may be right about the flywheel nut torque, but I use this rule for the old 40hp OMCs. If the nut wrench is 1-1/16, then torque to 105 ft/lbs. If it's 3/4" torque to 60-65 (and then just a bit more).
The old crankshaft/flywheel setup on earlier BigTwin style engines (35hp, 30hp) was found to be inadequate partway through the 1960 model year when many 40hp engines crankshafts broke soon after being put in service. The beefier crank with the 105 ft/lb nut was introduced then as a fix.

Timing device 378966 is totally unnecessary. These engines are very forgiving about timing and setting to .020" works just fine. If you really want to get picky, you can actually use your flywheel as 378966, since it has timing marks on it just like the fixture. But rigging it up is more difficult due to it not being open. And it's hard not to throw off the gap when reconnecting the ignition coil anyway.

Why did you need silicone to hold the woodruff key? It should press into the slot on the crankshaft. A few degrees error on setting the flywheel doesn't matter (and can sometimes help!), but if it's excessive you'll get weak spark.

Re: Woodruff keys, timing and all that jazz

I checked my after market service manual (72)Just to see if they caught that change.They still had the smaller
motors to 35 hp with 60-65 torque with the 40s at 100-105.Pauls rule of thumb sounds smart.Go by the nut size.

Re: Woodruff keys, timing and all that jazz

I used just a smidgen of Ultra Black silicone to hold the key in place. It was too loose and wouldn't hold itself. I have a feeling that because you asked, that was probably a problem in itself. The new key I replaced it with is a snug fit. Why did the flywheel not turn the spindle and shear the key to begin with? I had started the motor many times on one cylinder before changing coils. It's not locked up, I still could turn the motor over by turning the prop by hand. So now I have a stripped #1 plug (came with the purchase that way), and a sheared woodruff key. I think the timing will be fine once I set the points to .020. Thanks guys!