2003 U320 Rust remediation in bay structure

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2003 U320 Rust remediation in bay structure

January 05, 2014, 01:16:32 pm

While working on the HWH system, I noticed that the rear edge of the bay outer (lower) "skin" had come loose making it possible to see the metal structural members. I did not like what I saw - RUST!

I had checked the bulkhead bolts and knew they were fine, and that there was no bulkhead separation, but the fact that there was a lot of rust on the bay tubing that was bolted to the lower frame made me a bit worried that a serious problem was in the making. So, now that I have the HWH job done, I decided to look into the rust issue.

The only way to get a good view of what was going on was to remove a section of the lower skin. Since the skin is a fiberglass reinforced panel, I knew I could reattach it using normal fiberglass repair techniques. Using a Dremel tool, a 6" wide piece was cut all the way across the rear end of the skin (Photo 1).

What I found was both bad and good. The bad was how much rust there was on the rear box beam and what had happened to the foam insulation. The good was that there was no rust jacking between the box beam and the chassis member, the good condition of the Rollocs, and the lack of rust on the box beam just in front of the rusty one.

While there was only a little rust at the center line of the coach, there was a lot of rust near the two sides (Photo 2).

I scraped off the loose rust (Photo 3 shows the pile of rust). I will treat all this area with Ospho, paint with etching primer, and seal in some manner as yet to be determined. Also, I'll have to figure out how to reattach the skin to the steel beams - probably adhesive and screws.

All the bolts looked good. A typical one is shown in photo 4. I tested all of them and could actually back them off a bit and retighten easily.

I guess the biggest surprise was what had happened to the foam insulation. As you can see in photo 1 there are blobs of blue stuff where the foam should be. This is hard-as-a-rock stuff. Don pointed out that this was blue foam that had been melted by some solvent such as diesel fuel that may have leaked into the area. I know there is a slight diesel smell in the bays, but thought this was just some overflow from the fuel tank or the AquHot. I never guessed that enough diesel had leaked to affect the insulation. I guess I'll drill some inspection holes in various locations to define the extent of melting. Don't know yet how to fix this. Probably drill holes and spray in some foam.

I wish this coach could talk so I would know what had happened during its previous ownership. Then again, maybe I don't want to know.

As repairs are made, I will post additional photos. I've been reading Don's posting on his bay rebuild. I hope I don't get into that.

Re: 2003 U320 Rust remediation in bay structure

Reply #1 – January 05, 2014, 02:00:27 pm

I think you are taking the right approach Jim... I thought Foretravel was already using 4 or so through bolts with plugs in the bottom skin for access by 2003. If the bolts all unscrew and retighten, it would be no great chore to re-drill some number (spaced around the trailing arm shackles) of the rolok holes out to 3/8" and use some high strength through bolts with 1/4" x 1.5" x 2" rectangular washers for added peace of mind. I would certainly advocate filling in the space with some sort of poly urethane insulation. This would help keep the bays heated, but maybe more importantly prevent condensation from forming on the steel.
Don

Re: 2003 U320 Rust remediation in bay structure

Reply #2 – January 05, 2014, 02:58:40 pm

Agree with Don.

Remove Rolocks one at a time and replace with the 3/8" bolts with the backing washers he mentioned. That will spread the compression load from the center of the box beam to the top and bottom horizontal portion of the beam.

Re: 2003 U320 Rust remediation in bay structure

Reply #3 – January 05, 2014, 05:30:26 pm

Thanks guys. Will remove Rolocs and drill holes for 3/8" grade 8's.

Don, yes, Foretravel (or somebody) has installed 4 through bolts in addition to the Rolocs on both my front and rear bulkheads. The used caps on the 4 holes drilled in the skin. I would have thought Foretravel would have installed the through bolts before putting on the skin, thus, there would be no capped holes. Maybe it's easier to do after the skin is installed. Anybody out there with a 2003 - do you have 4 capped holes in the skin at the front and rear bulkheads?

Re: 2003 U320 Rust remediation in bay structure

Reply #4 – January 05, 2014, 06:03:52 pm

Yes, I've got the four caps for each, front and rear. I believe this was done by the factory, post build, after it was learned it could be a potential problem.

Re: 2003 U320 Rust remediation in bay structure

Reply #5 – January 05, 2014, 06:34:50 pm

Yes, those are the Foretravel plugs. Be aware, they are NOT waterproof plugs. They need to be sealed with a sealant such as polysulfide to be waterproof.

You can also remove them to inspect condition of the box beam.

Brett

Re: 2003 U320 Rust remediation in bay structure

Reply #6 – January 05, 2014, 07:19:12 pm

Quote from: Jim McNeece – January 05, 2014, 05:30:26 pm

Thanks guys. Will remove Rolocs and drill holes for 3/8" grade 8's.

Don, yes, Foretravel (or somebody) has installed 4 through bolts in addition to the Rolocs on both my front and rear bulkheads. The used caps on the 4 holes drilled in the skin. I would have thought Foretravel would have installed the through bolts before putting on the skin, thus, there would be no capped holes. Maybe it's easier to do after the skin is installed. Anybody out there with a 2003 - do you have 4 capped holes in the skin at the front and rear bulkheads?

Grade eights are brittle and we learned not to use them when a sideways shock load could occur. If we had a flywheel failure the scatter shield bolts would shatter if grade eights.

Bob

Re: 2003 U320 Rust remediation in bay structure

Reply #7 – January 05, 2014, 07:59:04 pm

Still think I will stick with grade 8's. Basis: Grade 5 vs Grade 8 Fasteners | TineLok

Re: 2003 U320 Rust remediation in bay structure

Reply #8 – January 05, 2014, 08:50:43 pm

Quote from: Jim McNeece – January 05, 2014, 07:59:04 pm

Still think I will stick with grade 8's. Basis: Grade 5 vs Grade 8 Fasteners | TineLok

I agree just grade eight supertanium bolts were banned by NHRA for scattershield use I all I am saying. Stronger but brittle.

Bob

Re: 2003 U320 Rust remediation in bay structure

Reply #9 – January 07, 2014, 02:30:45 pm

Quote from: Jim McNeece – January 05, 2014, 07:59:04 pm

Still think I will stick with grade 8's. Basis: Grade 5 vs Grade 8 Fasteners | TineLok

Jim,
Just an option, and yes I know that it is unpopular, but as an engineer, you can easily calculate that Grade 5 (and Grade eight) will easily exceed the compression yield stress of the 1.5" box beam horizontal cross section. Therefore, the critical characteristic becomes corrosion resistance, not bolting material strength.
I used SS bolting and so does Extreme, for that reason.
The 3/8" SS BOLTS ARE ALSO PLENTY CAPABLE of exceeding virgin material yield strength, if you overtorque them.
Priorities,
Happy New Year,
Neal

Re: 2003 U320 Rust remediation in bay structure

Reply #10 – January 07, 2014, 02:32:43 pm

Neal,

I have no problem with the strength of SS in that application.

But introducing another metal asks for galvanic corrosion, with the box beam being the anode (sacrificing to protect the more noble SS).

Brett

Re: 2003 U320 Rust remediation in bay structure

Reply #11 – January 07, 2014, 02:48:24 pm

Agree, Brett,
But James and I went through the exercise and proved (to ourselves, at least) that the proximity on the galvanic scale was miniscule to the point of being well within the uncertainties of not knowing actual material metallurgical compositions and the post fabrication contaminants that the joint had accumulated.

Also, the sacrifice would be in the immediate vicinity of the SS BOLT, which is no longer as important as with the Rolocks. With through bolting, that is properly backed by square or round load distribution washers, the crush (yield) strength (horizontal members, top and bottom of the box beam) become the controlling factor.
Neal

Re: 2003 U320 Rust remediation in bay structure

Reply #12 – January 07, 2014, 06:54:01 pm

I kind of live by the "if one is enough, why not use two" rule. Bolts are cheap. A dozen 3-inch grade 8's plus nuts are only $12.

The problem I'm having is finding thick, square washers of the right size. Most are 1-5/8" or 2" square. The only 1-1/2" ones I've found are $4 each and you have to buy 25 (Fastenal). Any suggestions?

I don't have access to a drill press, or I would make my own. It's really a pain drilling 1/4" plate with a hand drill. May have to go to HF and buy their $69 drill press (used to have one and it worked just fine).

Re: 2003 U320 Rust remediation in bay structure

Reply #13 – January 07, 2014, 07:15:38 pm

When I repaired my front bulkhead I had a local machinist make up the square washers that I needed. Still have some left, not sure how many but I can send them to you if you want them.

Roland

Re: 2003 U320 Rust remediation in bay structure

Reply #14 – January 07, 2014, 07:16:29 pm

Jim, Why not buy drilled strip at somewhere like Ace Hardware and cut off pieces to length. Looks like the stuff plumbers use to hang pipe but much heavier gauge. I have seen this in four or so foot sections with holes every inch or so.
Gary B

Re: 2003 U320 Rust remediation in bay structure

Reply #15 – January 07, 2014, 07:51:57 pm

Quote from: Neal Pillsbury – January 07, 2014, 02:30:45 pm

Just an option, and yes I know that it is unpopular, but as an engineer, you can easily calculate that Grade 5 (and Grade eight) will easily exceed the compression yield stress of the 1.5" box beam horizontal cross section. Therefore, the critical characteristic becomes corrosion resistance, not bolting material strength.
I used SS bolting and so does Extreme, for that reason.
The 3/8" SS BOLTS ARE ALSO PLENTY CAPABLE of exceeding virgin material yield strength, if you overtorque them.

Aren't all ss bolts grade three?

Re: 2003 U320 Rust remediation in bay structure

Reply #16 – January 07, 2014, 08:22:37 pm

Jim, my answer to those sq washers at Fastenal is buy them. Heck of a lot better than buying a drill press and metal. $100 and you get the job done and you are saving the labour anyway of someone else doing this job, which is worth a heck of a lot more. Go get them then you are done!! To me there comes a point were you just put out a few bucks extra.

John H

Re: 2003 U320 Rust remediation in bay structure

Reply #17 – January 07, 2014, 08:30:20 pm

I doubled up on the 316 stainless I have used so far. They are inexpensive if ordered from ebay and plenty strong.

A good 18-8 stainless bolt should be about the same strength as grade 5 bolts. I wanted a bit stronger so went with the 316. Plus they are just about immune to any road chemicals. Here is a chart with grade comparisons: http://www.boltdepot.com/fastener-information/materials-and-grades/bolt-grade-chart.aspx

Here is a stainless steel comparison chart: http://www.electronicfasteners.com/pdfs/techarchive/stainlesssheet.pdf

Everything you ever wanted to know about fasteners: http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf

Pierce

Re: 2003 U320 Rust remediation in bay structure

Reply #18 – January 07, 2014, 08:41:52 pm

Just to add another wrinkle: we used cad plated grade 8 bolts when we replaced the two broken Roloks on our rear bulkhead.

Also, I had the square washers made at a local fab shop per Brett's specifications.

Re: 2003 U320 Rust remediation in bay structure

Reply #19 – January 07, 2014, 09:07:08 pm

I used ARP SS bolts that are claimed to be stronger than grade 8. Made each washer out of 1/4 inch scrap plate steel custom cut with my table saw and metal cutting abrasive blade to fit as large as possible each bolt hole . Used drill press to cut holes in backing washers.

Re: 2003 U320 Rust remediation in bay structure

Reply #20 – January 07, 2014, 09:23:54 pm

Yup, any machine shop can make the square washers. I had a shop cut strips just less than 1.5" wide. Cut into lengths with hack saw. Used a drill press to drill.

Re: 2003 U320 Rust remediation in bay structure

Reply #21 – January 07, 2014, 09:24:55 pm

Bob, check out these stainless steel bolts... ARP Stainless Steel Bolts 623-4250 - Free Shipping on Orders Over at Summit
These are what are holding the basement of our coach and bulkhead together.
Don

Quote from: Caflashbob – January 07, 2014, 07:51:57 pm

Aren't all ss bolts grade three?

Re: 2003 U320 Rust remediation in bay structure

Reply #22 – January 07, 2014, 09:30:50 pm

Quote from: acousticart – January 07, 2014, 09:24:55 pm

Bob, check out these stainless steel bolts... ARP Stainless Steel Bolts 623-4250 - Free Shipping on Orders Over at Summit
These are what are holding the basement of our coach and bulkhead together.
Don

Cool

Re: 2003 U320 Rust remediation in bay structure

Reply #23 – January 07, 2014, 10:31:09 pm

Don,

One on each side of the coach would more than do it. Cheap if you consider what the original Rolok fastener has cost so many owners.

Pierce

Re: 2003 U320 Rust remediation in bay structure

Reply #24 – January 08, 2014, 12:48:03 am

Shear strength on a low carbon 3/8 Bolt is over five ton, It will crush the Box section you put it through, So dont tighten them too much,

Rust is your biggest threat, Galvanised or Zinc bolts would be ample, Stainless is overkill, But for the price of them, By all means put them in, $20-00 extra max for all the bolts needed in Stainless,

Make sure there are no ledges for water to sit on, Thats where the problem starts, and condensation can find its way out, A drain hole some where,

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