Page last updated July 17, 2008



Mercury Propeller Replacement

There are several propellers out there to choose from. I chose for their propeller selection and internet selection engine. It guided me in the right direction based on engine manufacturer, year and Horsepower.

I chose to go with a 14 pitch, 11.25 diameter Michigan Match Aluminum Prop (Part number 032041) for $112.00. There were cheaper ones available.

There are several others discount stores out there, so take your time and research. For the older Mercury 650, I ordered my propeller and it ended up needing a propeller adapter kit / prop nut kit. I could not identify the correct one based on internet information. All the adapters had no nut sizes.

I even went to local marine dealers and Academy's, and they could not help me. So to save some time and money, I created my own adapter kit based on a few cheap washers, cotter pins and castle nuts.


The problem with the new propeller is it lacks the nipples / tits to lock the prop nut from extracting due to vibrations and the shaft was too far out. Meaning that even if I torqued the nut down all the way, the prop would have about 1/8" - 1/4" play through the shaft. See photo to left and notice how the 13 splines protrude past the prop.

I needed some washers and a way to secure the prop nut.

So, my adventure begins.

As I was looking through the prop nut kits, I noticed they all used castle nuts.

Here is an example of what I needed as posted at This item seemed as if it would be perfect, but no size.

The castle nut is easy enough to find so I tried Lowes and they only had 5/8 fine thread and I needed course. I purchase the cotter pin, locking washer, and washer. I also purchased some 5/8 nylon locking nuts in case my first idea did not work.

I then tried Carquest and they had the 5/8 castle nut. Done with parts.

Make sure all parts are stainless steel, brass or coated with an anti-corrision finish. You can also spray anti-corrosion finish over parts.

I then placed prop with the largest washer first, then the propeller, then a washer that covered the rubber,

then the locking washer and the castle nut. I tightened and fitted so that I could get an idea of where I needed to drill the hole through the shaft for the cotter pin. Marked it with permanent marker.

I then removed lower unit and secured on my drill press using a belt and clamps. I secured the shaft by placing some wood underneath it.


I also had to grind down the spacing washer so that it would slide down the shaft.


I tapped a starting position with a punch and carefully started the press.

The hardest part is the start position. Once started, it is smooth sailing from there. Slow is smooth, smooth is fast. Watch out for heat build up and use cutting oil.



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