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Old 09-15-2020, 08:12 PM   #1
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rethinking things... subfloor install

I'm renovating a 68 Ambassador LY and mostly finished with a frame-on subfloor replacement. I found some 3/4" Blue Water 20 Coosa Composite board for a good deal. I'm securing the panels with 1/4" stainless steel bolts and nuts for the C-Channel and zinc-coated elevator bolts for the rest. I am trying to use only the original bolt holes and not create any new ones in the frame. I've put most of the bolts in the c channel, but I still have many elevator bolts left to put in.

Recently I got to thinking about road vibrations and the fact that the factory bent the original bolts at the top as a safeguard. And I'm wondering if I should rethink my logic here. I'm using the Permatex blue (medium strength) bolt locker. Will that be enough to hold for a regular amount of towing and usage? Should I consider using nylon insert nuts instead? And should I bend the bolts in the C-Channel as the factory did?

I want to make sure I'm doing this right the first time. Once I put in those interior skins and seal up the belly pan, it will be nearly impossible for me to check the bolts' status, let alone re-torque them.

I appreciate any advice you can provide.
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Old 09-15-2020, 09:51 PM   #2
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Well, surprisingly, stainless steel is not the best choice where it is going to be in contact with aluminum, and water may be present. The affinity for stainless steel to corrode aluminum is many times higher than non-stainless steel.

The other part of the question, in terms of locking nuts to bolts, why not use the thread locker that is practically permanent, (as you never, ever want to access them again anyway)? Or maybe just a big blob of Trempro or butyl goo, or something like that.

Then again, maybe you are over-analyzing it, and you are risking never getting the project finished. I have this problem too. My trailer isn't finished either...

good luck!
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Old 09-15-2020, 11:32 PM   #3
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Well, surprisingly, stainless steel is not the best choice where it is going to be in contact with aluminum, and water may be present. The affinity for stainless steel to corrode aluminum is many times higher than non-stainless steel.



The other part of the question, in terms of locking nuts to bolts, why not use the thread locker that is practically permanent, (as you never, ever want to access them again anyway)? Or maybe just a big blob of Trempro or butyl goo, or something like that.



Then again, maybe you are over-analyzing it, and you are risking never getting the project finished. I have this problem too. My trailer isn't finished either...



good luck!


Yes, I do over-analyze everything! Haha, mostly when I'm not an expert in the world of Airstream restoration. Always second-guessing myself!

Anyway, good to know about the high potential for corrosion Stainless steel, Aluminum, and H20.

There's probably a thread about this, but since I'm on the subject of bolts. Should I just go for regular steel bolts or the zinc coated for the Channel bolts and is there a certain grade bolt I should look for?

Also should I be using a locking washer? They didn't seem to use one from what I could see when pulling the old bolts. I've read they actually don't work and can increase the likelihood of nuts turning loose. https://www.boltscience.com/pages/he...ingwashers.htm

I am leaning towards your suggestion of using the red bolt locking fluid.

Thanks
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Old 09-16-2020, 06:17 AM   #4
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Wonder if you could coat the hardware after install with Por15 to prevent corrosion? Or if you could tape or somehow cover the ss bolt where it touches Al to prevent Contact corrosion.
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Old 09-16-2020, 06:50 AM   #5
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I guess you could use a small rubber washer on top and bottom. Or, just squirt a little Tempro or any polyurethane caulk as your installing. Underneath I just put a dab of caulk once I tightened the elevator bolts to keep the nut from backing off.
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Old 09-16-2020, 10:26 AM   #6
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Stainless to aluminum corrosion

When using bolts for attaching the C channel to the frame, the type of metal is important to choose. Obviously an aluminum alloy bolt would be best, but they are not strong enough for this application. Stainless steel is your next best choice due to it's inert characteristics. Zinc, copper, brass and other alloys are much worse due to the galvanic properties. The corrosion comes from a galvanic reaction between the two dissimilar metals where the aluminum acts as an anode and your stainless bolts act as the cathode. If you're familiar with how a battery works, the anode supplies electrons (corrosion/oxidation is loss of electrons) and the cathode /positive gains electrons. This all being said and back to your question. I would use lock washers and tack weld each nut(I did). Now spray coat them with a good paint, POR or Flex seal. Why? The galvanic reaction can only happen with water being present that acts as the transfer method for the electrons. This all being said, my 75 had steel elevator bolts and steel self tappers through C channel into the wood which resulted in almost ZERO corrosion to the C channel. Are we over thinking? Probably!! I'm 63 and won't be using this for 45 years, so I'm not too worried.
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Old 09-16-2020, 10:58 AM   #7
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Zen Stream,
Not directly related to your question but if shell remains attached to floor frame, be sure subfloor extends beneath channel at bottom of frame. It's integral to the whole shebang staying together. I did shell on and found that getting sub flooring beneath shell was a challenge.

Good luck!
Jim
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Old 09-16-2020, 11:12 AM   #8
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fasteners...

I don't normally post but I read this and wanted to comment.
A couple of points...Yes you're over thinking. First, if you were to bend over your stainless bolts, they stand a good chance of either cracking or breaking. Stainless bolts are brittle.

You can use lockwashers under the nuts. Just as effective as nyloc nuts. If you really feel that there's a chance (slim) that they'll loosen then put some locktight on the threads.

Your trailer isn't going to be used as a submarine so painting them with POR is WAY overkill. We've rebuilt many Airstreams and we use lockwashers, Steel bolts and nuts. Good for another 50 years.
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Old 09-16-2020, 12:30 PM   #9
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Zen Stream,
Not directly related to your question ,but if shell remains attached to floor frame, be sure subfloor extends beneath channel at bottom of frame. It's integral to the whole shebang staying together. I did shell on and found that getting sub flooring beneath shell was a challenge.

Good luck!
Jim

Yep replaced it all. I have full sheets spacing the width of the AS. I got them under that channel. Difficult when it's a frame-on but I puzzled it out. Definitely building a gantry and lifting the shell next time. Would save me loads if time. Haha
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Old 09-16-2020, 12:36 PM   #10
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I'd use stainless Nylok nuts
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Old 09-16-2020, 12:46 PM   #11
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So I'm getting that I could replace all those stainless steel bolts, but if I just did something to coat them, that would be adequate, and I don't have to redo a bunch of work. I have plenty of small cans of por15 and need to do some touch-ups on the frame anyway. If I paint the bolts as they are, then the stainless steel washer will still be in contact with the channel, but if I POR15 it and around it, water won't get in and then no corrosion? I could also see the trempro working pretty well in that same application.

I'm just curious now... What standard type bolt assembly used for the C Channel? Just regular steel with a lock washers like dwinik suggested? I'm ok with doing things over the right way. Haha
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Old 09-16-2020, 01:47 PM   #12
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In relative terms Stainless 316 grade 1/4" bolts attacking to Ali and the Ali being in relatively large area size to the bolt size is going to be "for me" anyway the best choice off fastner with added protection from a soft red thread lock to give anode cathode isolation plus resistance to vibration. I'm planning to look after future me 50 years from now so I need not redoo :}
I'd pay close attention to preventing seepage from seams n rivits if it remains unpainted, Captain Tollies Creeping Crack Cure rescued me, you would be surprised how much water a loose rivit head can supply and there is the major cause off corrosion. Water with salts perfect ellectrolyt...
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Old 09-16-2020, 02:56 PM   #13
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I have used stainless fasteners...rivets, machine screws and self tappers for years on both our AS's with no galvanic corrosion concerns...stainless being the preferred method.
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Old 09-16-2020, 04:24 PM   #14
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I'm a boat builder, so I use a lot of stainless fasteners. If you use blue locktite and nylock nuts you will have very little worry about corrosion problems even when directly fastening to either mild steel or aluminum. 316 alloy fasteners are not necessary for an RV unless you expect prolonged saltwater contact. 18-8 stainless is a lot less expensive and plenty strong enough and very corrosion resistant.
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Old 09-16-2020, 05:35 PM   #15
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OK stupid observation.
Isn't the frame STEEL? Is galvanic corrosion an issue with any kind of steel screw?
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Old 09-16-2020, 06:01 PM   #16
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Types of corrosion, Explained by NASA👍
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Old 09-16-2020, 08:00 PM   #17
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If your worried about the nuts backing off and allowing the bolt to loosen, why not just double nut them?

I used stainless bolts, nuts and washers.
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Old 09-17-2020, 08:44 AM   #18
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Types of corrosion, Explained by NASA👍
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Thanks for brushing us up, Bob; I was getting a little rusty.
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Old 09-17-2020, 10:19 AM   #19
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Thoughts from the auto industry... self-etching primer is usually zinc rich and a very effective corrosion inhibitor, I spray a shot on my c-channel hardware after they are tight. Mcmaster-carr sells several corrosion inhibitors that are very effective. I highly favor nylocks over lock washers and many have some sort of coating already on them. If you can find them, the elevator bolts with "fangs" are awesome if you're working alone. Must admit corrosion issues are not as severe here in Colorado, also prep is everything...
Best, Mark D
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Old 09-17-2020, 12:12 PM   #20
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Thoughts from the auto industry... self-etching primer is usually zinc rich and a very effective corrosion inhibitor, I spray a shot on my c-channel hardware after they are tight. Mcmaster-carr sells several corrosion inhibitors that are very effective. I highly favor nylocks over lock washers and many have some sort of coating already on them. If you can find them, the elevator bolts with "fangs" are awesome if you're working alone. Must admit corrosion issues are not as severe here in Colorado, also prep is everything...
Best, Mark D
All really good input here everyone!

On a side note, I really like the idea of "fanged" elevator bolts! Im assuming they have a couple teeth sticking down from the bottom of the flange? That would work well for me because I'm using coosa composite for a subfloor and my current elevator bolts often have a hard time gripping without wood. Most go in fine but some strip themselves out and need to be held from above. Makes a one person job into a 2 person job. That's the kind of stuff that keeps me behind on this build haha.
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