Scoliosis, Crown, or?

[MacDad]

Are the main frame rails designed with an arch to them with the high point between the wheels?

Both rails on my '72 Sov 31' have almost 2" of crown in them.

My first panic reaction was that the frame is bent, and that may be the case, but then I thought it is odd that it would be so evenly bent. Then I thought about floor joist and roof truss' are usually crown until loaded.

I know that the fresh water tank, refrigerator, furnace, and roof A/C are all right in the center over the axles so MAYBE the crown is supposed to be there?

What are others experiences? Stressed member?

[MacDad]

Sorry if I wasn't clear...my shell is off of the chassis and I am referring to a bare skeleton frame still sitting on axles and the front tongue jack.

Should the frame rails be laser flat or is there a spec for crown?

On our trailer there is a crown with the high point right at the center of the axles.

I do not see any bowing or distortion sideways or vertically of the frame rails at all. Just a crown front to rear.

[Mixter]

It is my understanding that shell actually holds the frame up. Assuming that the frame is good and solid.

My '76 27' had a crown prior to removing the shell, from which I wll attibute to many outriggers failing. Also had 2 cracks in the main frame rail, which allowed the outriggers to sag even more. (see pic)

Since the frame over the axles was more rigid, the weaker parts created the bow.

Even with my frame redone, though, the rearward frame aft of the axles did sag an inch or 2. I jacked it up tight when bolting the shell back on, and its looks MUCH more straight and level. I have not done any type of testing,and the shell is back on, the

[Mixter]

Soooo... to further answer your question.... Yes, there may be some arch in the bare frame, but the finished product should be flat once its all buttoned back up.

[MacDad]

Thank you guys.
Since posting the question I went out and played a bit more and I am pretty confident that most, if not all, is just flex in the frame. I can jack up the back up until the wheels are off the ground and the flex goes the other way.

The main frame rails are solid with only the last few feet under the rear bathroom showing a bit of rust which my adopted father who is a certified aircraft welder is going to replace for me.

If there is any actual bend I believe it is from bad axles. I did the jack up test and the trailing arms only drop 1/2" so I think the rubber/polymer/elastomer in the axles has dried out and the bouncing or banging on basically solid axles may have put a small kink...

I want to ask the experienced folks if adding a punch plate would be a good idea?

The front 5' or so has a backing plate welded inside the C-channel frame. I am considering adding that all the way back. The weight would be negligible and the bracing would really add structure but not total rigidity. Just an idea

[Wabbiteer]

If someone has ever tried to jack the trailer lifting against the ladder frame rails it leaves a dart/fold in the lower 'C' profile of frame that will pull the end(s) down in a droop - just something to check.

[MacDad]

Took the trailer to my welding shop and we decided that to add some strength without adding too much weight or too much rigidity we are going to cut out the handful of bad rusted areas and weld in new channel, and then continue the inner box plate all the way down. The stock frame has about 5' of the frame boxed with some 3/16" x 5" hole punched plate. We are going to run that the whole way back while working the frame level with jack stands. We are also going to add some angle behind the large plate that braces the axle support just for added strength.

Then it is redeck it and start the reassembly.

[perryg114]

I would plate in that whole back side of the beam where they have the stuff with holes in it. Adding angle to the axle mounting plate won't hurt. My trailer has tanks in the axle area so things are pretty tight on mine. It won't hurt to connect the outriggers together at the ends and bolt through that into the lower part of the trailer if you are doing a frame off. Are you going to add holding tanks to the trailer? The main structural connection to the shell is at the back and it is not that great. The shell does support the frame but this connection is easily damaged by too much weight (full holding tanks), dead axles, and rust and neglect. The plate on top of the bumper that goes under the back of the trailer is a major leak point and you might want to consider getting rid of it. It funnels water under the rear sub floor. Also getting rid of the pink fiberglass sponge is a good idea. The frame will sag without the shell to support it. The newer trailers have a 5" box beam from the rear wheels on back or in some cases two 5" channels welded together to form a box. The early 70's trailers used the open single C-channel and I think the metal with holes in it to plate it to some extent.

Perry

[MacDad]

Excellent info Perry. I did not want to OVER do it and cause a rigidity issue that may cause rivet popping. If the newer ones do indeed box the channel then there should be no issue. Great news.

We are not planning on running water/septic tanks. I have been rethinking that back and forth, but I think it is the simplest and cleanest way for our needs.

If the kids need to serve somewhere more remote or disaster ridden with no hook ups we can always use the existing tanks on the ground under the trailer which could make dumping waste and filling fresh that much easier without having to move the trailer. Win/win I think.

I believe I will use standard insulation under the floor since it is thick enough to give good R-factor. The walls will be a new ecofoam product I have found. It will be a pain in the a$$ to do but offers double the R-factor of fiberglass batts. Not cheap either, but anything for my kids and it will add value for any possible resale in the future.

[RickDavis]

They did have some frame problems back around that time. Look down the frame underside and see if there ar any ripples in the plate the axles bolt too. Also for any signs that the center partition was pushing up through the ceiling. Also misaligned cabinet doors. That may be harder to tell with the body off. The fix was to suspend the frame from the ends and install reinforcing plates over the axles. They may already be on the 72, not sure.

I don't know how much sag there would be in the frame , body off but 2 inches sound like a lot and the longer trailers were known for bent frames. I bent the frame on my 69 29 footer when it was only three years old trying to get up a hill on a washboard dirt road.

[perryg114]

I would not use fiberglass anywhere especially in the floor. The rigid foam stuff works well. I don't even have insulation under most of my floor yet. I have not found a need for it. My belly skins are bolted on so I can get in there to inspect things and add insulation if I need to. Airstream leak and that water always ends up in the floor and is held there by the pink fiberglass (aka stinky pink stuff).

Perry

[MacDad]

I was planning on using the encapsulated stuff, it is a tube of plastic filled wwith stinky pink...lol.
I am hoping to have NO leaks...but stuff does happen.

Maybe I will go to the blue or white styro based panels.

[Mixter]

Plan for leaks.... you will have them.

[perryg114]

The plastic coating won't last forever on the fiberglass mats and water will find its way in and can't get out.

Perry

[MacDad]

So we stripped the chassis down to just the welded components and the rear axle, easier to move around on one axle since weight is not an issue at the moment. We are ordering new axles soon since we determined that bad axles was definitely the cause of the excessive crown with a slight buckle between the axles.

At first glance there seemed to be no bends or anything serious that would cause the crown, but on further inspection after we media blasted the entire chassis did show a slight kink in the rail stiffener that is welded to the C-channel frame rails. The stiffener is a large thick plate welded to the side of the C-channel over the axles and there was a buckle between the axles on the curb side.

Our fix was to tow it down to my friends welding shop in Redondo Beach and jack up both ends of the frame rail and pull down right at the kink. While it was stressed we clamped a piece of 2"x3" heavy angle iron to the inside of the rail stiffener between the 2 axle mounts. As we welded the angle we kept re-clamping and sucking in the kink as we welded towards the buckled spot. By the time we finished you could not really see any more kink in the top rail.

After working out the main issue we took 1/8" x 5" plate and cut pieces to fit all the way from front to rear in between the cross braces or truss pieces or whatever they are called. We then stich welded them with about 1.5-2" welds every 6-8" staggered top and bottom. The channel iron spreader bar that was welded at the rear of the chassis was rotted so we replaced that with square tube steel.

The end result is a chassis that looks dead straight now and while it still has some flex is MUCH stiffer than stock. We are very happy with the end result and can move forward with much more confidence in the foundation of the trailer.

Thanks for all of your input...more questions to come.

BTW, I bought a gallon of POR15 to coat the chassis to convert any spec of rust the blasting did not knock off and help prevent future issues. We will use a dauber style brush on a heavy wire to coat inside the now boxed frame rails since there is still some access every 24" or so. I will then top coat paint the exposed areas of the frame a nice silver later to UV protect it.