Elevator bolts—new issue/quandry

[steve46]

I am about to install the finish floor on a 1976 TradeWind and have a situation I have not seen addressed elsewhere. The subfloor has been entirely replaced in a shell off refurbishment with 3/4” dryply/plytanium plywood and secured with new elevator bolts. The bolts are countersunk and the holes will be filled before the finish floor—Marmoleum sheet—is installed. The elevator bolts were tight when the floor was installed, but now, 2+ years later, all of the bolts can be tightened more, even just using hand power on the Phillips head bolts. I want to ensure that the bolts stay adequately tight forever, and that they do not ever rise up to disturb the finish floor.
My plan was to remove each elevator bolt, one at a time, put red threadlocker/Loctite on the threads then reinsert and tighten, however I believe that by the time the bolt gets down to the frame opening, all of the threadlocker has come off onto the plywood—a few test bolts done this way were easily loosened by hand after a few days. Another option suggested may be to fill the existing holes and then put down another thin 1/4” subfloor running the other way on top. I don’t really want to put on another floor because of weight, cost and effort if that is avoidable.
Can anyone offer their firsthand experience or a thoughtful opinion on resolving this matter, please? I’m not certain that it truly is an isssue though (when I removed the original 40 year old subfloor, the old elevator bolts seemed secure and most came out without much effort, and for the most part I am using the original holes) and am trying to avoid the “well, I wish I had known about that earlier” situation, but perhaps it’s not a big deal and, as my aunt would say, “don’t borrow trouble”.
Thanks for any input that will raise my comfort level.

[Bubba L]

You could use nyloc nuts or double nut. On ours I just used the regular nuts, tightened everything down then spotted a little Parbond caulk on the threads below the nut to keep it from backing off. You may want to check on the standard installation guide for Marmoleum. I believe they recommend 1/4” plywood over your subfloor. Anything will telegraph through the Marmoleum so make sure all is flush. Some have used Ardex Feather Finish. Good luck

[steve46]

One point I neglected to mention: the belly pan has already been installed therefore I have no access underneath to attack a solution from that point.

[Crackerman]

Did you use an adhesive between the plywood and frame? If so, just tighten bolts more.

If not, the loctite sounds like a plan.

[Bill M.]

I think your terminology is incorrect. My understanding is that the “elevator” bolts are the bolts through the C channel around the peremiter. I do not know what they call the bolts into the frame through the subfloor. Tecks comes to mind.

I think that the bolts did not loosen so much as the plywood shrunk causing them to be loose.

I think your plan is okay and that you will get enough thread locker through the plywood to help. It could be that the original holes through the plywood were a bit small. Ideally you should be able to push the bolt through the plywood rather than thread it in. That leaves thread locker in the grooves. Maybe the original installer did not get the plywood pulled solidly down against the frame. You want to be sure the plywood is not catching in the threads and is being pulled down against the frame.

[dieseleagle]

Elevator bolts are similar to carriage bolts except that they have a large flat head approximated one inch in diameter. They are so named because they were designed to fasten together the rubber belts in a grain elevator application. Once installed in the field of the plywood and if the belly pan is in place to prevent access from below there is no practical way to get ahold the head to turn it. If you drilled the head and used an extraction tool to turn the bolt the nut would either just spin underneath or it would fall off into the belly pan and you would be unable to refasten. Assuming access from underneath I always just use bolts that are long enough so I can just whack the "tail" enough to slightly bend the bolt, which prevents the nut from moving. That is what the factory did back in the day.

[steve46]

Thanks for the replies. The plywood was laid flat upon the frame and no adhesive was used, only the elevator bolts secure the floor to the frame. The plywood may have shrunk, therefore the less tight elevator bolts now. The holes in the plywood have not been enlarged (and I really didn’t want to do that), so threadlocker comes off, I believe, before the bolt end reaches the opening in the frame. I have no access to the underside of the trailer as the belly pan is installed. My options seem limited to 1) determining how to get threadlocker down into the hole (ala a WD-40 type straw?)—any ideas?, 2) retightening, then filling the holes with a floor leveling product and calling it good, and 3) putting another subfloor atop.

Am I missing anything? Am I overthinking the whole thing and is it not a valid concern? What would (or did) you do?

Thanks.

[Re-Pete]

That sounds like quite the dilemma. I feel for you. You mentioned Philips heads, Are these "thread cutting" screws or bolts with nuts holding them? Mine had elevator bolts around the floor channel, but the subfloor field was fastened with thread cutting screws. If this is how your's is fastened then additional tightening might be sufficient. My original screws were very secure when I removed them. Best of luck.

[steve46]

I call them elevator bolts and that is how they referred to them when I purchased replacements at the Airstream factory. They all get threaded into holes in the frame/chassis, but not around the perimeter. Mine were also all tight when I removed the originals after nearly 40 years. I put the replacements into the existing holes in most cases.

Here is what I have decided to do:
—Retighten all bolts by hand
—brush some Titebond wood glue on the exposed portion of the plywood where the elevator bolts are countersunk
—use Bondo to cover all holes and seams (I used plytanium/dryply which is tongue and groove).
—call it good to now install the sheet Marmoleum product which gets glued down.

Thanks, all, for your input.

[Re-Pete]

Again, Best of luck!

[steve46]

I will share what I learned along the way toward getting the finish floor installed. I did use bondo to fill the elevator bolt holes and around the perimeter where the floor had been routed to accept the shell channel and that seemed to go well. I did realize that my primary subfloor (tongue and groove Plytanium DryPly) had a wax coating on it and as a result, to ensure proper installation and adhesion, I cut and fitted an additional 1/4” subfloor to be attached atop the primary one. While it involved additional cost, effort and weight, it was a necessary step. The finish floor—Marmoleum sheet—was professionally installed and now looks great. Next step: trimming the bottoms of the already constructed interior walls to start the rebuild—much more satisfying to do things that people can actually see! Here are a few photos of the floor adventure.

[perryg114]

I would have just urethaned the sub floor and called it done.



Perry

[waninae39]

elevator bolt have no no Philips head
flush on one side
thread on the other

imho, i would have used nylon nuts on the other side
loctite should not wipe off as bolt pushed through