6 replies to this topic

[Old Crow]

(Note- the title says jack plates but I meant jack brackets)

 

Hi, all-

 

I've just finished stripping and painting the jack brackets on my 01 Hawk and am ready to put them back on.  These are the older one-piece brackets attached with lag screws.  I had noticed a few screw-heads broken off but by the time I got the brackets off, I had a total of 10 of the 48 screws broken off at the head due to rust.

 

The thread http://www.wanderthe...rusty-brackets/ covers this topic pretty well and provides a photo of the more durable screws used by FWC since about 2010. (see photo below)

 

I made the mistake of going to my local Fastenal and coming back with a few #14 self-tapping screws like that in 410 stainless steel (the only thing they had in stock than plain steel).   Fortunately, I was curious about the differences in stainless steel materials and that led me to http://www.preservat...metals/PGC.html .  The table shows 410 stainless steel would not be a good choice.

 

Does anyone have detailed specs or part numbers on the newer screws (or other recommendations)?

 

Also-- any tips on using the self-tapping screws in the threads created by the lag screws?  I note, for example, both lag screws and the self-tappers don't necessarily like to go in straight.

 

-OC

Attached Thumbnails

• 

Edited by Old Crow, 02 August 2015 - 02:24 PM.

[ntsqd]

Classically stainless steel threaded into aluminum is a bad idea. More so in wet environs, less so in dry climes. What happens is the same for both climes, but the rate it happens at is slower to much slower in the dry. Seems like few outside of the ocean going marine set know about this as I frequently see it done outside of that realm.

 

I note from your galvanic series link that galvanized steel is very close to aluminum. That would be my choice. When I worked in submersible electrical connector design I was told to keep the galvanic potential of mated metals to less than 0.25 electron-Volt maximum with under 0.1 eV being preferred.

 

Other than experientially arriving at wanting the hole to be 0.005"-0.010" larger than the screw's body diameter I've no pearls of wisdom. I prefer to use machine threads when ever possible, but at this tube wall thickness that may not be possible.

Edited by ntsqd, 03 August 2015 - 12:48 PM.

[PaulT]

You have at least three metals to consider. The screw, the jack bracket, the aluminum frame and possibly the aluminum skin if it is a different type of aluminum. Any washers should also be of concern. In addition to the galvanic corrosion, there is the possibility of crevice corrosion where the fasteners press together. Crevice corrosion can occur without the screw head showing obvious corrosion in its surface.

As ntsqd says, salt water boaters are typically more aware of the issues because they take all the fastened metals & immerse them in salt water.

Paul

[Old Crow]

Thanks for the replies!

 

After looking through the possibilities in the Fastenal catalog, I decided I was in over my head and ordered the newer-design screws from FWC.  They are 1/4 - 14 x 2"  screw of C1022-grade steel with a Climaseal organometallic polymer coating over a base coat of non-electrolytically-applied zinc (I kid you not).  After reading through all that, my only fear is I won't have a technologically-advanced-enough driver to put them in!

 

And thanks for the crevice-corrosion info.  I didn't even know it's a 'thing'. In any case, a 20-per-cent failure rate of the bracket-screws on a 14-years-young camper suggests something out of the ordinary is going on.  Galvanic corrosion?  Crevice corrosion? Plain Old Rust? Who knows....

 

- OC

 

PS- I tried to attach a photo of the old screws but keep getting the message.... The server returned an error during upload 

 I'll try later.

[Old Crow]

Here's a photo of the original lag screws I'm replacing with the newer self-tapping design.

 

 

 

I assume the white powder is aluminum oxide but it seems a bit oddly distributed.

 

The stub to the immediate right of the broken-off heads stands out as the only one with rust its full length.

 

The ends of the broken-off heads show they were almost completely rusted through and so broke off very easily with the first application of torque.  I wouldn't be surprised if some fall off as we drive around. 

 

(Note- Not all 48 screws are here. I couldn't find the others. I believe the short ones were replacements by previous owners)

 

-OC

[Old Crow]

Photos of one of the brackets after stripping off the powder-coat....

 

   

 

 

I was surprised to see the odd-looking 'tracks' of rust under the powder-coat.  I'm guessing insidious old Mr. Rust finds his way in through some little break in the powder coat and as rust forms it pushes out on the powder-coat a bit, opening up pathways to intrude further.

 

The tracks didn't seem to be phased at all by wire brushing (manually).  After trying several wire brushes mounted in a drill motor to no effect, I ended up using a Dremel motor with grinding wheel attachment to remove them. 

 

Bonus  photo-- the key to getting off the powder-coat was Aircraft Remover from my local Autozone.

 

[Old Crow]

Just getting around to updating this thread with results from re-do of my jack brackets---

 

I ordered 50 of the newer-style screws from FWC.  The cost seemed reasonable at $12 but shipping to my home in PA was another $13 so $25 total for the screws.

 

I was able to extract all but one of the ten broken-off screws.   I got two of them out with extractors but drilling the stubs for the extractors was very slow and I couldn't keep the drill bit centered on the stub.  Once I switched to the dremel-cut slot method for the others, I was surprised to find the screws weren't 'frozen' as tight as I expected.  The corrosion that takes out the head is localized there.  I tried to be careful to cut a good, clean slot with the dremel wheel and cut it in far enough for the screwdriver blade to engage well. Then I'd try a few back-and-forth turns to break it loose. And once broken loose, most backed out easily.  A few made me wonder whether the screwdriver would break off one of the slot sides and that happened once.  But by then the stub was out far enough to grab with with vise-grips.

 

The new screws have a zinc and Climashield finish but I still used a dollop of anti-seize for the installation, both for lubrication (while cutting the new threads) and as an anti-corrosion measure.  

 

If I had it to do again I'd use a driver rather than a ratchet and socket to install them so I could more precisely control the angle as the self-drilling TEK screw starts in.  I had some problems with the screw not 'wanting' to go in fully perpendicular to the surface.  Once that starts, it just seems to get worse and is difficult to correct.  I had thought I'd first run a tap in but the 1/4 - 14 thread isn't a common size and I couldn't find one locally (but didn't look very hard).

 

I should also note I had contacted FWC for a price on a set of the newer two-piece brackets.  The old ones have a fold in the metal that seems to be begging for corrosion to start there. Shaw replied to note they're an inch shorter than the older one-piece ones and have a different hole pattern and number of screws. I decided to just go ahead with my old ones.  I did, however, caulk the crevice before installation.

 

-OC