Thruster Anode Stripped Thread

[Metric Rider]

While changing the sacrificial anodes on the thrusters I have run into a problem (apparently of my own making!).

I was successful on removing the centre bolts and then I was able to remove the old anodes with application of some penetrating oil and light prying with needle nose pliers(being careful not to insert the pliers too far so as to avoid damage to the threads). I cleaned the surface behind the anode with emery paper to ensure good contact with the new anode. The front anode was reinstalled with little difficulty (I used blue threadlock and tightened enough that there was no movement between the hub and the anode)

When installing the new rear anode in spite of trying to be careful I have somehow managed to strip the thread in the housing ( I believe it is brass). There is some thread left but not enough to properly tighten the bolt. I am hoping I am not the first person to have this issue and am looking for solutions:
1) can I use red threadlock or some other material on the bolt threads that will hold the anode in place
2) or can I use a slightly larger bolt with maybe a coarser thread
3) or heaven forbid, replace he housing!

Also have the following questions:
a) Since I could find no specified torque setting for the bolt am I correct in assuming it need to be snug enough to keep the anode from freely spinning so there is adequate contact?
b) Is it possible that there was debris in the end of the bolt hole that prevented the bolt from tightening down the anode before it stripped the thread?

Thanks in advance for any suggestions / solutions

 

[Brian B]

I would contact Imtra for advice on the stripped threads, I'm sure they have dealt with it before, this is their contact info
http://www.imtra.com/contact-us.htm
Did you try using the old screw? at one time there was a slight difference between the old screw and new ones.
Using a helicoil could be an option but I don't know about the access to install one and then there is the issue of mixed metals in salt water. A new gear leg is very expensive.
I use a plumbers sink basin wrench to easily remove the zincs, like this http://www.homedepot.com/p/HDX-Basin-Wr ... /206184138

 

[Metric Rider]

Thanks for the contact info!

 

[knotflying]

Let us know what Imtra says. My thought would be to go with a slightly larger diameter hex screw and retap the thread using a bottoming tap. Or perhaps retap with a bottoming tap using the same thread first and see how that works out. Unfortunately every time you replace the anode you will have to drill out the hole to receive the larger head. That's still cheaper than a $500 new shaft and the heartache of removing the stern thruster.

 

[baz]

Metric Rider:

I don't have an answer for you on your issue.

However, what I will say is that it's very important to check the thruster anodes regularly. They are small and erode (or can erode more quickly depending on the waters your boat is kept in) fairly fast. If left unattended for too long the female threads will get eaten/eroded and no matter what you do the holding bolt will have nothing to hold onto. With this in mind I had my thruster anodes replaced when they reached around 50% gone. Repairing a thruster is expensive. During my first year of R-25 ownership I established how long the thruster anode would last at my marina, and then had my under water diver person check the anodes at the mid point of the time period.

 

[Metric Rider]

The thruster anodes removed were much less than 50% gone, I don't think my issue with the threads was corrosion. Does anyone know the bolt and thread size? Has anyone used Loctite thread repair?

 

[Brian B]

Another tool that may work is a thread chaser. You will see them online, maybe if you know a mechanic they may have a set. Sidepower tech support at Imtra will know the size of of the thread. Hardware stores usually have a board with nuts and bolts attached showing the diameter and thread sizes you can match up. I know Lowe's has them in the hardware section.
Check out this video I just saw
https://www.bing.com/videos/search?q=th ... ORM=VRDGAR

Let us know how this works out for you.

 

[Metric Rider]

Good video, thanks for the link. I will post my final solution, right now assembling all the good ideas I can before I proceed.

 

[Brian B]

Here's another idea I thought of. With the zinc installed I think that bolt only engages a few threads. Try it without the zinc and see how it feels before it bottoms out. If it engages good threads then you only need a slightly longer screw which you could cut down to fit.

 

[Metric Rider]

I took Brian B's advice and contacted Imtra re the problem. They responded very quickly via email with a service bulletin that gives a straightforward solution to the problem. In short the solution is to red loctite in a stud and and then fastening the anode with a washer and nylon lock nut (the anode does have to modified). Not sure how to post the service bulletin but is very good information to have for anyone in this situation. Thanks Brian for your suggestion to contact Imtra

 

[Brian B]

GREAT!! That's good info for the memory bank which is kind of full. Can you email that service bulletin to me at brianbel@verizon.net
Thanks.

 

[knotflying]

I looked at the Imtra SB. My opinion is I would try to salvage the existing threads and then worse case scenerio go with a longer hex bold of the same size. This will avoid having to modify the anode with each change. Just save the old hex bolt each time and you are golden.

 

[Metric Rider]

I like your thought on using the original bolt. I am still sitting on my fix for a couple of days as boating has not started in this part of the country and there is no great rush. A product I have found "Loctite Thread Repair" (video on youtube) looks like it has possibilities.

 

[BB marine]

I just removed the zink's from bow and stern thrusters. I trailered the boat last year,the most it sat in the water was 3 days at a time. Over the winter I painted the bottom and now finishing priming and painting the metal components that will be in the water so I can keep the boat full time wet. I removed both zincs and both props to prime and paint the brass thruster housings. I was amazed at how much sink was worn away. The most the boat was in the water total 30 days last year. The rest of the time on the trailer. I also was surprised that there is only 5 to 6 threads holding the zinc on to the housing. When I saw this post I checked the thread size It appeared to be a 10-32 machine screw. I measuring with a pitch gauge. When I went to run it thru a die it wanted to cut the threads. Metric possibly 5mm. I can see how it would be easy to strip out the brass threads with a stainless screw. I think I would use a HeliCole insert . It is made of 304 stainless ,easy to install, permanent and more durable then the brass threads. I used them for years in aluminum outboard housings when the threads were so badly damaged from corrosion. My second choice would be to put a permanent stud in the housing and them modify a larger zinc to replace the OEM zinc. I also noticed that the anode is Aluminum not zinc .
Brian Brown
Cutwater 26
PORT-A-GEE

 

[Metric Rider]

Saw a new thread re stripped threads for mounting a zinc to a thruster which reminded me I did not post my final solution for my stripped threads. I did end up using the Loctite thread repair kit with apparent good results. The plan b was the procedure recommended by the manufacturer