Prop seal change on Honda BF50A

[welderman]

I recently pulled my MacGregor 26X out for repairs after noticing oil slick when I dropped the engine down. Draining the gear box showed me a milky mix of water and gear oil. Further inspection showed that the prop thrust washer was chewing into the outermost water seal on the gear box. What had happened was that corrosion in that area had pushed the seal into the thrust washer. After downloading a service manual I proceeded with the replacement of the inner and outer seals on the gear box. This engine is a 1999 or 2000. There is a special tool to remove the end nut on the case. It costs around $200. I made one from a plumbing part for around
$10. The information for this is on google. It turned out the end nut was so corroded that it would not budge so I removed it bit by bit with a Dremel tool. After the end nut is removed you are supposed to be able to pull out the prop shaft assembly along with the 2 seals. The prop shaft assembly was frozen in and it also would not budge. In the end I was able to removed the 2 seals without removing the assembly and replace them. I was able to clean the threads up somewhat for the end nut. When installing the seals I used Permatex ultra blue gasket maker to seal them in. This was necessary especially for the outer seal as the case assembly was badly corroded. My suggestions to those who try to do the same repairs are this. Don't pull out the end nut as it probably won't come out anyway. Also the prop shaft assembly gets corroded and won't come out without damaging it or the gear box. The seals can be removed without scratching the prop shaft.

 

[tcwest]

I know this is an old thread but i have a 1997 BF50A, with somewhat of a similar issue. I changed my water pump and lower unit oil, and pulled the prop to run the motor in a barrel. After pulling the prop i noticed that the prop shaft end retaining nut was warped and badly corroded. When i put a screwdriver on it two teeth broke off. The rest seems very solid and I’m inclined not to touch it further and take my chances for another season. Shaft is not leaking, no water in the lower unit oil, and the shaft seems to spin freely and normally.

I was just curious if you had any further issues with yours? And specifically wondering if you were able get a new nut in the corroded threads? I believe my threads will be so corroded that a new nut won’t thread in, so again, I’m inclined not to touch it.

Any thoughts?

 

[jssailem]

take my chances for another season.

I would get the shaft threads cleaned. The nut and the shaft are likely dissimilar metals. The nut sounds like it is the source of corrosion. Get the shaft threads cleaned and get a new nut.

If you choose the “Take my chances” path, what do you think is the worse that can happen if you happen to be on the water and a strong gale is approaching as you seek a safe harbor to weather the storm?

 

[tcwest]

My concern is that the threads are so corroded that i won’t be able to clean them well enough to thread on a new nut. Or it’s possible the threads are gone. Based on what I’m seeing with the small section where the nut is gone, i think it’s likely. So if i remove the rest of the nut and can’t clean out the threads enough to screw on another nut, well, then I’m …. !

I’m just curious if anyone else has had this problem. Assuming i can’t replace the nut, my options are to 1) assume that the corrosion is so bad the existing nut is “welded” in place and won’t go anywhere, 2) replace the lower unit, or 3) replace the motor. I’m leaning to #3 in 2024.

Again, just looking for anyone else that may have a similar issue and how it was addressed.

 

[jssailem]

if i remove the rest of the nut and can’t clean out the threads enough to screw on another nut, well, then I’m …. !

I’m one that feels a corroded thread means the nut is compromised. If the nut comes off the thread and the thread is worn then you should be happy to discover the problem. Failure of the nut or threads means your prop is coming off.

The option might be you could save the shaft by having it rethreaded. A prop shop could tell you.

That depends on the metal.

This type of corrosion is electrolysis. That means the shaft is subject to internal decay. That means nothing is good. You need to have the shaft inspected.

 

[tcwest]

The prop shaft if fine, the issue is the lower unit housing that holds the end nut - that’s where the corrosion is. If I do get the nut out and can’t thread in a new nut, the lower unit is shot. If the nut is somewhat “welded” in due to corrosion, it won’t last forever, sooner or later it’ll decay to the point that it falls apart, but I’m not there yet. I think it’s solid enough it won’t go anywhere. So I’m just curious if anyone else had this problem.