Outboard propeller shaft run out?

[Skip Newsom]

I managed to acquire the heart break of a bent shaft... I've done some searches and seen differing numeric values on how much run out is acceptable.
I have the Sealoc manual that covers this motor but I can't seem to locate the value in it anywhere...

Here's the specifics.
2008 Yamama 20 HP 4 stroke outboard (F20ESH) with that sweet, sweet electric starter.
The shaft was .038" out of round measured at the end of the prop shaft just before the prop nut threads begin.
Using a porta-power I've applied force to the high side of the shaft at increasing shaft deflection values and leaving the force applied for as much as an hour.
I got .005 gains 3 times, and then smaller and smaller gains to the current .015 out of roundededness where I stopped for the night.

Any thoughts or data on what value I should shoot for (other than zero, that would work I'd bet) ???

here's my rigging:

[DanielDudley]

Skip, I don't know nothin about nothin, but if it turns freely without screwing up the bearings you are probably OK. I am sure you are well within that type of tolerance. It's going to have a hard time showing balance issues when it is pushing water.

If you really want it straight, take it out, but it isn't a Swiss watch.

[asphaltgambler]

My opinion - not sure what's acceptable but close to .040 sounds like too much because that will be leveraged out to the end of the blades - certainly enough to cause out-of-roundness and vibration. I think that .015 is acceptable in something like that. I'm OCD about similar things and I would be happy with the result.

[rfuerst911sc]

Were you experiencing excessive vibration before you started straightening the shaft ? If the answer is yes then throw a prop on it and see if the vibration is gone or much less than before . I'm going to assume you had a prop strike , if so then don't rule out the prop being " off " also .

[berettafan]

recommend checking in with The Hull Truth forums. some very knowledgeable guys there.

[Skip Newsom]

Thanks for the replies and thoughts!

I did have a couple of prop strikes, one of my favorite lakes was lower than normal and I ran it at an idle into mud trying to get back to the boat launch ramp... twice. Not one of my proudest moments.
I've not had a chance to run at full speed yet to assess vibration.
I noticed the run out after I took it out of the water and spun the prop by hand.
The next day I was warming it up for an oil change and the prop shaft was clearly bent, I removed the prop and measured just the shaft.
I'll check some more on the Hull truth forums... there was one post I saw that said .007 run out was max, that was on a higher HP merc though.

Here's a vid of the prop at idle before I started the straightening process:

[berettafan]

Can’t imagine mud doing that. We hit all manner of stumps and mud with our duck boat to the point where the prop is damaged and have yet to experience any issues. That’s on a 40hp merc but wouldn’t think other small outboards being much different.




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[Skip Newsom]

It may have been this way previously, I may have just not noticed it before... and it was not ordinary mud, the North Cascades creates super mud!

Being more than a bit anal about mechanical stuff I need to fix it or have it repaired to the correct specs.
I did post on the hull truth forums this morning, hopefully I'll get some additional guidance.
One of my annual week long boating camping trips is 7 days away!

[Skip Newsom]

Progress, several cycles of increasing shaft deflection has brought the outta roundedness from .038 to .010,
I'm doing another cycle now at .235 deflection, then I'll check, measure, rinse and repeat in an hour as needed.

The Hull Truth forum folks replied to my post there with two values (.007, .002).
.002 measured at the center of the shaft came from the Yamama manual, since I'm avoiding pulling the shaft I'll be mighty pleased if I can get to .004 at the outer edge of the shaft, mighty pleased indeed.