Rehubbing Props for Small Outboard Motors  

 

 

 

 

If you use/play with old outboard motors long enough, you will come across a prop that the prop has become separated from the hub.  With many of these nearing or over 50 years old, your chances of finding even a used prop will be near ZERO and probably the prop shops can't help you.  If they could the price would in all likelihood be more that the value of the motor.

 

If the rubber hub has just come unbonded, I have cleaned  everything and epoxied it back into the prop hub cavity.  But if the rubber hub as been deteriorated so badly , OR ruined by the owner, then other methods need to be looked at.

 

I was approached  by the owner of a 1965 Evinrude 5 hp motor, that when he tried to pull the prop, some previous owner apparently never had it off or at least never lubed the propshaft.  The prop was seized so tightly that in pulling the prop, it came unbonded.  But the rubber and brass hub was still seized onto the shaft.  OK a propane torch was used , which in the process burned the rubber off, but the hub came off.  No problem, just find a used prop.  Well this motor was only made for 3 years and did not have a gearbox (forward/neutral/reverse), which meant the prop rotated the opposite (LH) as most all other motors of near that size.   And he could not find a prop shop who dealt with that old or size of motor.   Well, I was never accused of not wanting a challenge, so I agreed to repair it.  The only reason I did, was that I had purchased an identical motor a few years ago, rebuilt it and had not sold it yet.

 

 I did a lot of asking at a local contractor's hardware/lumber yard to see if I could find a caulking that would set up hard.  NOPE, as just the opposite, they want it to stay pliable inside, and hard to the touch on the outside skin.  And the cavity was so large (without the rubber) that "Liquid Nails" would not really work.  My only resort now was to use fiberglass resin.  But this required some preparation.

 

 

OK, Where Do I Start ?  :  First was to clean everything, and get rid of any old rubber or grease.  This entailed inspection of the prop, which I found a plastic/Nylon shim inside against the rear inner end.  This had to come out and the whole inner part sandblasted to remove rubber and any grease, but to also supply a rough surface for the fiberglass to adhere to.  

On this prop, the shaft size was 1/2" while the rear, threaded nut was 7/16".  There is a large washer with the 7/16" hole that fitted in a recess on the rear, so a stub shaft was made to accommodate these dimensions

 

Then the bronze hub was placed in my metal lathe and COURSE threads ran on the center section, again for the purpose of ensuring better bonding.    

 

My plan, was to injecting fiberglass resin in between the hub and prop.  But, this resin is very liquid and to keep it from running out the rear, I used the stub shaft as alignment along with the washer and by before it was in place, applied a ring of caulking around the rear outer hub.  Applied some Vaseline on the outside under the washer to protect any unwanted adhesion, then slid the hub down the shaft, clamped the shaft in a vise allowing the caulking to settle down as the prop was held with the front pointing UP.   I then let this set up for a day.

 

Next, I used a 1/8" carbide cutter in my Dremel tool, and on this model, the shear pin slots were on the front/larger end of the hub.   Here, off the ends of the shear pin slits, I cut in with the Dremel tool cutter about 1/2 depth of the cutter.  Then after the caulking was set on the rear, I drilled the rest of the 1/8" hole in the prop inner housing edge aligning with these precut shear pin cuts, making a 1/8" hole on each side down into the cavity.

 

Now at a farm store I purchased  a couple of 12CC hypodermic syringes, which had the same outside dia. of my 1/8" drilled holes.  I mixed up about 10CCs of resin and a few drops (like 4) of hardener, mixed that and quickly plugged the outlet hole of the syringe with a finger, then poured in the resin and then inserted the syringe nozzle into the hub hole and slowly injected this resin.  If you dally too long and or the weather temperature is warm, you may not get it all injected.  I then quickly cleaned the syringe with Acetone and let the hub set up.  An hour later did it again, until the cavity became full, as indicated by it coming out the other hole.

 

 

1986 5hp OMC prop, stripped down with the hub on the left

 

I then cleaned up any excess unhardened resin using paper towels and a number of Q-Tips.

 

 

Here you see the resin fill holes

 

Another One  :   OK, now we have another hub, but this time it is off a 1957 3 hp Evinrude Ducktwin.  Again with the possibility very slim in finding replacement parts.  This prop had numerous ridges inside the prop housing, with more numerous ridges on the outside of the hub.  There was a rubber coupler that looked like a cogged automotive timing belt but with cogs on both sides that slid in between both the hub and the prop tying them together.  Over time (60 years), this rubber coupler deteriorated enough that it allowed the prop to slip on the hub.

 

Here I used the same method as previously, only here the owner had tried to fix it by squirting silicone sealer in between the three parts, which can be seen in the photo below.  The hub was wire wheeled to remove the silicone and rubber, but the prop required sandblasting. 

 

 

Here you see the damaged prop and cleaned hub.

 

 

This motor again uses a shear pin, but on this one it is recessed into the prop about 1/2" deep.   Again a stub shaft was lathe turned to fit the hub when doing this project, which allowed me to, before the fiberglass was set, the prop could be rotated on this shaft and eyeballed to rotate concentrically as nearly as possible.  This prop was a bit different in that it had a hard plastic (?) bushing at the rear that pretty well sealed the fiberglass from running out as was on the 5hp prop.  And the prop shaft was smaller (7/16").  Here I also used the 12CC hypodermic syringe to inject the resin where I wanted it, instead of it running over which would have required a cleanup.  These syringes were sacrificial but for a price of under a dollar was worth it.

 

Here you see the two parts fiberglass resin boned together

 

 

 

Copyright © 2017 LeeRoy Wisner  All Rights Reserved

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Originated 08-13-2017, Last updated 09-19-2017
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