Repairing My Own Prop

Bassn7

Seaman
Joined
May 25, 2015
Messages
65
Before I buy a new prop I would like to attempt to heat and bend the blades out myself. It's only a $70 prop for my old Mercury 9.8. What tricks do I need to know so I don't snap off the blades? 2 of the 3 blades are slightly curled in. I just need to bend them out. Thanks to all that can help me.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
Do you have any knowledge/experience involving Metallurgy? Without a pitch block, the odds of getting the blades close are far from good. Bending Aluminum back often results in cracks that will lead to blade breakage. Balancing the prop may also be difficult. As you said "It's only a $70 prop". Don't let anyone try to sell you a prop for a 9.9, It will not fit, ever
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,296
Plenty of $20 props for 7.5 and 9.8 out there on CL. I ended tossing a few because i tried selling for almost a year

I have an engineering degree and access to everything except pitch blocks and I wouldnt attempt to work on a prop.

running a bent prop is a fast way to damage the leg

Buy a good prop, or get it repaired by a prop shop
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
I'll attempt a prop of my own if not bent too bad. I figure there's nothing lost if I try and it breaks vs. sending it to the shop or replacing it. I don't use heat, ever.

I do use a small hammer (for good control) and a sheet metal dolly (think hand held anvil w/smooth surfaces) that's at least as heavy as the hammer. Preferably much heavier. Just remember aluminum hardens as it works, becoming much more likely to crack, so think about what you're doing.
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
15,413
I would go for it. You have nothing to loose.

I would have at my disposal the following:
Good quality anvil with horn
heavy ball peen hammer
heavy dead blow
couple blocks of hardwood
contour gauge

I’ve done two with reasonable results. Then again, my education and professional background is in metallurgy and metals fabrication which includes hot and cold metal smithing.
 

harringtondav

Commander
Joined
May 26, 2018
Messages
2,438
I have a couple 3" diameter x 4" steel cylinders I got from my pop's house. I think they were old fire door weights or rollers. I've had luck in the past straightening minor bends using these (like dingbat's anvil horn to straighten the bend and eyeball the cup. I did it cold. Sneak up on the bend from the heavier hub side of the blade and work toward the edges. If you get in a hurry you'll likely crack a blade.
 

SkaterRace

Senior Chief Petty Officer
Joined
Mar 20, 2016
Messages
709
I've done it before and it was mostly me breaking the prop and then replacing it. I did however once bend part of one back and cut the rest off with an angle grinder :D prop had a little wobble to it after that so I got only about 200 ft out on the water before returning the the dock and replacing the prop.
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
If you approach this with some tech in mind, I don't see why you couldn't do it. Obviously you want all the blades to be the same in every dimension for starters. How you arrive at that is with small increments at a time. You can use a bar for the prop shaft diameter and verify the blades are the exact same length. Then another tool to verify the curves are the same. Maybe if you have some dial indicators to accomplish that. And after you get those identical, then comes balancing. A cone balancer would be perfect for that. I have been thinking about using a feed back setup to the computer to graph the prop blades for such a repair. Where there is a will there certainly will be a way. I like trying such things out myself. Pitch blocks would be great, but you could even make them with some castings. So many ways...
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Probably not a big deal at this level of engine size etc...but surely for the price of a new prop...it’s not worth it. These things need to not only be equally pitched, but balanced too. Never going to be just right otherwise.
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
Joined
May 19, 2001
Messages
26,019
Okay I will pass along a repair idea that I have actually seen work as crazy as it sounds......

HIGH quality cement
plastic
5 gal bucket

If you can get a new prop in good shape cover it in plastic
mix the cement leaving it thick and place in bucket
Press the prop into the cement to make a mold of the prop and blades (Don't submerge it but a tiny bit over the blades can be okay)
Let it dry - remove the prop

Cut away the bucket and you will have a mold of the prop and blades

I have seen this done when I was in Missouri and people used to hit rocks in the river - bend a prop - remove it - use the mold and hammer it back into shape with the original pitch

I have seen it work and it's fairly cheap
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
Yes, there are lots of ways. Once you get the blades all the same, balancing is not an issue.There are so many static ways to balance a prop. Just have to think!
 
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