2004 Air Nautique SV211 Flight control tower rubber knob on won’t unscrew

[columbus68]

I have a 2004 Air Nautique SV211 Flight control tower rubber knob on won’t unscrew. It is in the closed position and I can barely get it to turn. Regardless of the number of turns I can get, the knob does not show any distance unscrewing from the tower. Attached are two photos. One is the replacement knob and bolt. The other is a closeAttached are two photos. One is the replacement knob and bolt. The other is a close up of the outside of the knob looking up from the bottom after removing the cap insert on the knob. Any suggestions on how to get the knob off?

[bturner]

All depends on how bad you want that knob off. If I understand correctly, you've pulled the plastic part of the knob off in the second picture and what we're looking at is the stud and arbor that the knob is/was pressed into.

If that's the case, most likely what has happened is galvanic corrasion between the aluminum tower and the stainless steel stud has occurred and "welded" the two together. In most of these cases the stud and the tower are now one and the only option would be to cut the stud flush to the tower then very carefully drill out the stud or try removing with the largest "easy out" you can safely use. You may be able to get the remainder of the stud out if you can break the threads loose but in most cases the corrasion is to the point where the threads and the stud are now one. Depending on how successful you are you could possible re-tap the existing hole but in most cases you likely have to drill out the hole and use an insert to maintain the same thread/size stud moving forward.

[columbus68]

The knob has not come off yet. The initial picture is a close up of the inside of the knob. There was a cap on the knob, but that is off.

[ScooterMcgavin]

I had this happen on one of my older boats and here’s what I did from a recommendation on here.
- first penetrating lube anywhere you feel will get to the stud. After waiting a bit I used a large channel lock pliers with a rag over the knob.
- The knob unscrewed from the stud but it came off and now I had to get the stud out.
- more penetrating lube and then vise grips on the thread of the stud, and finally broke the stud free from the tower.
- had to re-thread the stud with a tap and die set.
- used anti seize when putting it back together.
It was not a fun job, but it worked

[srock]

Use Mouse Milk penetrating oil. It's expensive but great for a frozen stainless/aluminum combo. Add a little each day for a week, then get to work.

[biacs]

My FCT always needed (or it helped) someone to jiggle the tower up and down a but to relieve the pressure on the knob/studs. These towers jiggle, bounce, sway the whole time they are in motion so they certainly need some TLC. If need be cut an access hole behind the bow cushions and tighten the anchors!