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Old 22-04-2013, 14:33   #1
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Stripped Threads on Mast

Kinda appropriate that I clicked on "New Thread" for this topic....

One of the mast-mounted halyard winches on our boat has failed. The base of the winch was cracked, and I saw the mounting was becoming loose. Upon removal, I saw that two of the four mounting screws were tight, but the other two were loose - and then discovered that the threads in the aluminum mast were stripped.

I've since ordered a replacement winch, but I have to decide how to handle the stripped threads. Barring aluminum welding approach, seems I have two choices: (a) Replace the 1/4-20 screws with larger ones, drilling and tapping the existing holes for the next size up; or (b) Go with a steel threaded insert, such as HeliCoil or the stronger Acme Keylocking Insert. While alternative (a) is the cheapest, I would likely have to drill and increase the size of the holes slightly in the base of the replacement winch, and possibly have to alter the larger screw heads (if the heads interfered with the drum operation). The inserts are a more involved and expensive approach, but I do have some concern over the strength of such inserts...I have no experience with either HeliCoil or the more expense Acme inserts. And there's a HUGE amount of force on a halyard winch!

Any thoughts or recommendations would be greatly appreciated!
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Old 22-04-2013, 14:44   #2
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Re: Stripped Threads on Mast

Why don't you patch the holes and move the winch up or down and re-install in new holes?

I had some "extra" holes at the base of my mast after re-arrainging some halyard blocks. I filled them in with JB Weld for aluminum. The holes were just above the mast step in the first 6" or so of the mast extrusion. After sanding the JB Weld, I masked with painters tape and primed and painted (aluminum color) the 6" section. I had some 1" blue striping tape so I applied the tape over the paint line. Looks really nice.
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Old 22-04-2013, 14:47   #3
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Re: Stripped Threads on Mast

Can you rotate the new winch base and drill new holes. Had to do that when i changed the jib winch as the holes didn't line up. Mast sections are plenty strong and can take a few extra holes.
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Old 22-04-2013, 16:10   #4
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Re: Stripped Threads on Mast

Quote:
Originally Posted by voxxmd View Post
two choices: (a) Replace the 1/4-20 screws with larger ones, drilling and tapping the existing holes for the next size up; or (b) Go with a steel threaded insert, such as HeliCoil or the stronger Acme Keylocking Insert.
The threaded inserts are dead easy to install and are plenty strong. They will be stronger than the original tapped aluminum threads. They are the 'proper' solution here.

They really are not any more involved to install than either putting in bigger machine screws or moving the holes. To install them you drill the hole out bigger and tap them, which you would have to do for the bigger machine screws, and then screw in the threaded inserts, and then the original size machine screws will thread in perfectly.
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Old 22-04-2013, 16:40   #5
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Re: Stripped Threads on Mast

Greetings and welcome aboard the CF, voxxmd.
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Old 22-04-2013, 17:34   #6
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Re: Stripped Threads on Mast

Time Serts are also an option. They are THE factory approved repair for cylinder head bolts on many engines, so you know they're tough.

NEW TIME-SERT 1/4 - 20 SAE Thread Repair Kit # 0140 : Amazon.com : Automotive

And are available in stainless.

TIME-SERT Inch Stainless Steel Insert 1/4-20 X .500 Part # 01404 : Amazon.com : Automotive
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Old 22-04-2013, 18:05   #7
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Re: Stripped Threads on Mast

It is likely that the holes did not strip out. Rather the stainless screw was incompatible with the aluminum and water caused galvanic corrosion which destroyed the aluminum threads. Tefgel and other thread dopes are available to help slow this process.

I do not recommend putting stainless inserts into an aluminum mast. The metals are not compatible and galvanic corrosion is a serious risk. There are aluminum threaded inserts available such as the Rivnut. They can be easily replaced in the future. Any decent machine shop that deals in aluminum will have the tools to install them. There are specific inserts for each metal thickness so you have to get the right one for your situation.
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Old 22-04-2013, 18:11   #8
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Re: Stripped Threads on Mast

You can install nutserts or rivnuts without the special tool. I've done hundreds with and without the tool. You can just thread in a bolt that's 1 1/2" longer than the depth of the insert with a nut up near the head and a couple greased washers between the nut and the insert. Hold the bolt and tighten the nut down to compress the insert, then unscrew the nut and the bolt. That said, there's no way that I'd bother with inserts. I' turn the winch 1/6th turn and mark, drill, and tap new holes.
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Old 23-04-2013, 01:04   #9
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Re: Stripped Threads on Mast

yup...Rivet nuts. I would use the same holes of course. Adding more holes as suggested, only weakens the area.
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Old 23-04-2013, 03:49   #10
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Re: Stripped Threads on Mast

Agree with the above

1. Do not drill new holes - weakens the area of the mast
2. Drill out existing holes and use aluminium inserts
3. Ensure you put tefgel between inserts and mast so if/when you need to replace inserts you can remove them

It is a very straight forward and easy repair. Only real issue is to ensure that when you enlarge the existing holes that you stay on center so that when the inserts go in the bolt holes will still line up.

edit: One thing also is to figure out how to reduce the pull on the winch that is stripping out the lower screws. Are you leaving a line under heavy tension on the winch? If so consider adding a clutch to all lines fed to this winch so you that it isnt under constant heavy load
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Old 23-04-2013, 08:49   #11
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Re: Stripped Threads on Mast

As most have said, inserts are the way to go... More holes I don't like.... BUT!!! Surprised nobody has offered what I think is the best solution... Especially for a high load halyard winch...

A backing plate... Or two if the entrance holes on your mast are too small for one plate (likely) It's a bit of a pain, but pre-make your plates to fit the mounts on the winch... Thread a stiff wire through one mounting hole out halyard entry... pull plate inside mast tight against inside wall, and loosely connect the hardware with a longer fastener in hole #2.... Assuming 2 plates for either side... Pull feed wire back out thru halyard hole... Install 2nd fastener...repeat...

Takes a bit of wiggling, fidgeting and the like, but with a 1/4" aluminum backing plate in the mast... You will NEVER have to worry about this install again...
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Old 23-04-2013, 09:19   #12
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Re: Stripped Threads on Mast

I disagree with the use of aluminum inserts.

First, the stainless insert will be stronger, because the you will have a bigger diameter of stainless threads, essentially just as if you had used a bigger bolt. With an aluminum insert and stainless bolt you are just back to the original strength, which we know either stripped or corroded.

Second, If you use a stainless insert you will always be able to remove the stainless bolt. It will never freeze or corrode in a stainless insert. And since you don't need to remove the stainless insert, so it does not matter if it freezes (but as a note the heli-coils are the easiest to remove from any corrosion because you can 'unwind' the spring, which you can not do with the more solid inserts). If you use an aluminum insert the stainless bolt may cause corrosion and freeze in it.

Third, you can actually isolate a stainless insert from the aluminum mast better than you can isolate a stainless bolt. Because you don't need to remove the insert, you can use 'permanent' stuff like red locktite, which seals the insert and will not wash out. You want to be able to remove the bolt so you can 'only' use temporary stuff like tuff-gel, which does wash out over time.
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Old 23-04-2013, 09:25   #13
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Re: Stripped Threads on Mast

Quote:
Originally Posted by foolishsailor View Post
Agree with the above



edit: One thing also is to figure out how to reduce the pull on the winch that is stripping out the lower screws. Are you leaving a line under heavy tension on the winch? If so consider adding a clutch to all lines fed to this winch so you that it isnt under constant heavy load
Granted most of the load should be shear, but the part of the load applying torque putting tension on the lower bolts you are saying will be better held by one lower bolt of a single clutch, or 2 of a double, than the 3 or 4 sharing the load on the winch?
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Old 23-04-2013, 09:32   #14
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Quote:
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Granted most of the load should be shear, but the part of the load applying torque putting tension on the lower bolts you are saying will be better held by one lower bolt of a single clutch, or 2 of a double, than the 3 or 4 sharing the load on the winch?
The load is pulling less than 1/2 inch above the mast, versus 3-4 inches. The difference is leverage would vastly outweigh the difference between 1 screw and 3.

I have never seen a properly mounted clutch pulled out of a mast. Doesnt mean it is not possible...
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Old 23-04-2013, 09:46   #15
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Re: Stripped Threads on Mast

Regardless of how you fix it (I'd roatate and redrill) put lanolin on the screws and it wont occur again!
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