40hp shearing flywheel keys?

Bman1337

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So I went to tune my outboard today in a barrel because the idle just wasn't that great. It would pop back and die. So upon getting it fired up i was fighting getting it to sit there and idle long enough to tune. Well one of the times cranking the engine suddenly sounded like zero compression. Checked the plugs and pistons. Fine. Checked the reeds. Also fine. That's when I noticed the flywheel had sheared the key off. The flywheel is alittle marred up from spinning on the crank. And the crank is alittle as well. But nothing drastic. What I did notice when I took it apart was that flywheel nut came right off with a 3/8 drive ratchet and not much effort so I assume it wasn't very tight to begin with. So I went out to my local ace hardware. Grabbed another key. Now honestly I don't know if the ones from the hardware store are up to the task or not. But I threw it in. Torqued it down best I could with said 3/8 ratchet and cheater bar. It was a struggle because the flywheel kept wanting to spin. Anyway I got it where I thought it was ok. Fired it up. Adjusted the idle mixture screw because it was almost completely in. And backing it out the engine purred like a kitten. Perfectly smooth idle. No popping. No back firing. Would fire up with the bump of the key. I figured that back fire/popping is what caused to shear it off. Well I walked away satisfied with the results and came back about an hr later and the motor was struggling to fire back up. Think I flooded it honestly. Well the moment I hear the motor actually fire once it did it again. Sheared the key right off. Again the flywheel nut was looser than it should have been when I went to loosen it.
So what's going on? Not enough torque on the flywheel nut? Flywheel not mating to the crank good enough? Hardware store key not up to the task?
 

Bman1337

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And the crank itself is fine. Obviously the flywheel being aluminum and the crank steel all that happened was some aluminum got transferred. Cleans up good with alittle fine sand paper. The flywheel however the closer I look the more I believe it's gonna have to get replaced.
 

Bman1337

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Can these be lapped back to each other or is that flywheel too far gone?
 

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Nordin

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First you have to check that the flywheel key you use is the right one that fits perfectly.
If it is too big the flywheel will ride on the key and the taper do not do it´s purpose.
The key is only for right location of the flywheel and the taper is for holding the flywheel in place with the nut.
Before you put all things together you have to lap the flywheel to the crank taper.
Use valve grinding compound to lap.
Apply some compound to the crank taper and rotate the flywheel back and forth about 90 dgr then change the location of the flywheel a bit and rotate back and forth again.
Do this all the way of the crank taper then check the surface of the flywheel taper and crank taper.
You should perhaps see a grey smooth surface at both.
80% or more should be grey and smooth.
When you put all together you have to torque the nut to right spec.
I think the value is about 120Nm but check the value with a workshop manual.
If this not will work you have to change the flywheel but try to lap before you go for a new flywheel.
I have seen tapers that looked worse than yours and that has worked.
 
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Bman1337

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I plan to give it a go tomorrow. Gonna source the factory key tomorrow and give the lapping a go. I know for a fact when I re assembled I wasn't anywhere near the torque spec so the second sheering that occured on me must have been atleast partially my fault. I was trying to find the correct torque spec myself and I saw a few places saying pre 95 is 80ftlbs and 96 and up is 125ft lbs. Now that seems like a lot honestly and I'm not sure how I could hold the motor from rotating to achieve that torque. Put it in gear and stop the prop? Flywheels for there are tad expensive so I plan to try that before dropping the 200+ on a flywheel. Most are closer to 300.
 

racerone

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Use a flywheel turning tool to hold it.-----Agreed , the key locates it for timing.----The locking taper drives the flywheel.----Assemble clean and dry.
 

jerryjerry05

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Get a NEW flywheel nut.
In extreme cases you can use a BIG screwdriver placed in the bendix and the flywheel teeth to hold it in place.
 

Bman1337

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Get a NEW flywheel nut.
In extreme cases you can use a BIG screwdriver placed in the bendix and the flywheel teeth to hold it in place.
How crucial is the new nut? Is it for the same reason you replace head bolts?
 

Bman1337

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Well I did the lapping process and this is the results of 3 applications of compound. Cleaning everything up in between. Think this will do? Or should I be lapping it more? Can you lap too much?
 

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racerone

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Time to give it a try.-----Wipe any embedded compound off.----Install and torque.----Test run.
 

Bman1337

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Time to give it a try.-----Wipe any embedded compound off.----Install and torque.----Test run.
Yeah I'm probably gonna have to ship in a key. Neither local shop has got back to me about wether they have one or not. And the hardware store key didn't fit snuggly in the crank so I doubt it would do anything but shear again
 

Nordin

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Franz Marine will have the flywheel key, Crowley Marine too.
Partnumber 91800 I think.
 

jerryjerry05

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VERY!!!! IMPORTANT!!!!!
The nylon in the Nyloc nut has expanded and won't hold like it should.
You can try heating it up but you can also cook the top seal when you do.
Good chance it won't ever hold again.
 

ErSa

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An idea of holding the flywheel.
 

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Bman1337

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Wait the crank nut is supposed to have nylon? Because the one on it is just a plain plain nut. Nothing special about it.
 
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