BULKHEAD repair parts checklist

Topic: BULKHEAD repair parts checklist (Read 947 times) previous topic - next topic

BULKHEAD repair parts checklist

March 18, 2015, 05:41:38 am

Soon I intend to begin the bulkhead repair on my 95 U320. I want to make sure I'm ordering the correct parts for this job.

I have read the posts that deal with this repair, but still want to confirm the right parts as there seem to be differences depending on model year ( steel box channel iron, single or double width).

BOLTS: 3/8" X 3" length , about 10 per side. grade 8 , Zinc coated.
Nuts, matching lock washers, and flat washers. ( would stainless washers be advised?)
Would Stainless bolts (grade 2 - 300 series stainless) be a good idea?
With only 20# of torgue would they be strong enough? Do I really need grade 8

Flat iron to support through bolts (back up box channel iron edge for extra support): 1 3/8" (also read 1 1/4") X 1/8" thickness.
What width is correct? Is there room for a wider width?

Fine thread or course thread bolts?

Whats the best way to draw the tub sections tight when tightening the thorough bolts?

I never noticed any separation until after I jacked up the rear when doing brake and air chamber work in the back.
It seems that raising the rear put enough stress on the rusted bolts that they failed like buttons popping off an over stressed shirt.
After noticing sticking bay doors in the rear, I traced the problem to the bulk head separation.
The front bulkhead looks snug, but I will do the front also.

Thanks!

Re: BULKHEAD repair parts checklist

Reply #1 – March 18, 2015, 09:13:23 am

First, grade 8 bolts have a much higher tensile strength than grade 5. Like 13,900# for 3/8-16 thd or 15,800# for 3/8-24 thd. (Unfortunately I don't have my Machinery Handbook here, but I do have the Holo-Krome data slipstick)
Average torque to tighten a 3/8-16 bolt is 940"# or 78.33'#
Average torque to tighten a 3/8-24 bolt is 1060"# or 88.33'#
Average tension induced in bolts tightened to yield (fail) is 10,850# for UNRC thd and 13,900# for UNRF thd.
(Holo-Krome Company stats)
If tightening in soft materials where indentation is undesirable and might occur at 75% of torque, lower values should be used, but take into consideration that vibration may cause loosening. Recommend a locking solution on nut & bolt thds.

Re: BULKHEAD repair parts checklist

Reply #2 – March 18, 2015, 10:42:43 am

I used 3/8" 316 stainless with stainless nylocks at the other end with stainless washers. I bought a box of 50 so have been drilling two holes between the original. Inexpensive off ebay. If the rectangular tubing is solid, you won't have a problem deforming it when you torque them.

Our coach was just about rust free but had quite a bit of rust behind the big angle iron. I removed about seven and forced the bulkhead and the angle iron slightly apart and then used a Sawzall to clean out the rust. You can repeat it the entire way across. There was a LOT. Sandblasting followed by spray galvanizing will make sure it does not occur again. I don't like sealing the area as you can trap moisture in there. When and if I ever get time, I am going to space the angle iron about 1/16" from the rest of the bulkhead so it will drain water rather than collecting it.

You will need to check the tubing interior as your rust may have come from a compartment leak.

Rust and hydrogen embrittlement have already weakened the existing fasteners to a fraction of their original strength.

Failed fasteners will probably be inline with the tires with the center being OK. Don't ignore the front as I had several fail there on the passenger's side.

I don't place much faith in the torque wrench check. They rust into place and fail right where they go into the rectangular tubing.

Pierce

Re: BULKHEAD repair parts checklist

Reply #3 – March 18, 2015, 10:56:29 am

Guess I have too much experience with dissimilar metals from my boating, but I would not use SS on iron angle and the iron box beams.

And do not over-torque to bolts-- the walls of the box beam are 1/8" (when new-- rust will further degrade that) and you are torquing only on the inboard wall. That is the reason for the square/rectangular washer I mention in my write-up. You want to spread the torque on the horizontal portions of the box beam. Yes, grade 8 is probably overkill, with grade 5 providing ample torquing ability.

You don't mention how you will be sealing the holes in the bottom of the fiberglass. If just a few, the waterproof plugs are a good choice. If replacing all of them, perhaps glassing in a strip of fiberglass over the area makes more sense.

Also, you did not mention treating the rust-- and perhaps can not until you expose the area to see what needs to be done.

Re: BULKHEAD repair parts checklist

Reply #4 – March 18, 2015, 11:10:58 am

Let me guess... did you use just one safety stand on each axle end and were they placed in front of the duals next to the bulkhead? If so, as I have posted before in a few different threads, the teeter totter effect comes into play. Downward pressure from the safety stand pushes the front of the H frame down, rotating the axle assembly away from the front of the coach, which pulls on the trailing directly acting on the bulkhead joint. Likewise, putting stands behind the axel and letting the coach rest on them without stands in front of the axle will close the gap. I used this effect routinely when I was repairing my bulkhead joint.
Don

Quote from: Lon and Cheryl – March 18, 2015, 05:41:38 am

Whats the best way to draw the tub sections tight when tightening the thorough bolts?

I never noticed any separation until after I jacked up the rear when doing brake and air chamber work in the back.
It seems that raising the rear put enough stress on the rusted bolts that they failed like buttons popping off an over stressed shirt.
After noticing sticking bay doors in the rear, I traced the problem to the bulk head separation.
The front bulkhead looks snug, but I will do the front also.

Thanks!

Re: BULKHEAD repair parts checklist

Reply #5 – March 18, 2015, 11:36:57 am

Quote from: wolfe10 – March 18, 2015, 10:56:29 am

Guess I have too much experience with dissimilar metals from my boating, but I would not use SS on iron angle and the iron box beams.

Brett,

Here is a paragraph from SSINA, the Stainless Steel Information Center.
Quote:
"For example, if a window frame made of stainless steel and it is attached with carbon steel screws, the screws will probably corrode at an accelerated rate. If the area of the cathode (noble metal – stainless steel) is very small, and the anode (active metal – carbon steel) is very large, the current produced will be very low and the corrosion rate of the anode may not be affected. If the window frame is made of carbon steel and it is attached with stainless steel screws there will be very little, if any, galvanic corrosion."
End quote.

If the bulkhead angle iron were to be made of stainless and the bolts steel, there could be enough electrical potential to cause corrosion. But the other way around, the potential is very minimal.

More detailed information is available at: SSINA: Stainless Steel: Corrosion

Pierce

Re: BULKHEAD repair parts checklist

Reply #6 – March 18, 2015, 11:44:27 am

Just a comment: I would make sure to chamfer the holes where the bolt heads contact. Without a chamfer the standard manufactured radius under the bolt head can cause the bolt to register improper torque and put irregular stress on the bolt.

Re: BULKHEAD repair parts checklist

Reply #7 – March 18, 2015, 01:16:35 pm

Lon, I checked mine I had one rolock that turned. This weekend I installed 6 3/8ths Gr 8 through bolts in the rear (I did the front a couple of years ago). I can tell you get you a bunch of good 3/8ths bits the angle iron is hard. You will also need a magnet to find the sub frame pieces to know were to cut your access holes, unless you are going to open the whole area behind the angle iron. Also as Brett and others have said be careful tightening the new bolts they are way stronger than the box tubing.

Re: BULKHEAD repair parts checklist

Reply #8 – March 18, 2015, 01:47:21 pm

Little trick I learned from a Stainless Specialist guy. Running your drill at one constant high speed you run the risk of work hardening the mat'l in front of the drill point. Pulsate your drill--RPM up and down while exerting directional force. Works on any mat'l that tends to work harden.

Another tip: Use a center drill to start a hole in thin material. Cuts quicker, has a thinner chisel point enabling better penetration without the drill walking.

Re: BULKHEAD repair parts checklist

Reply #9 – March 19, 2015, 03:28:22 am

Thanks for all the help.

DON: I jacked the coach in the rear from the axle I can't remember exactly, but I think I did place jack stands in front of the axle to give me more room to work around the wheel. I will try your "stand placement behind the axle" when I want to draw the bulkheads together. Maybe ahead of the axle if I want to separate the bulkheads a bit to clean and treat the steel.

BRETT: I did not address the treatment and cleaning of the area because my main concerns in the post was to build a shopping list for parts I will need. I would appreciate suggestions on what kind of paint or covering to use when treating the steel. I probably will open up the entire width of the bulkheads to get a good look, and to make it easier for a complete repair.

PIERCE: As always, I value your wisdom and advice. I do like the idea of the SS bolts and associated hardware. I already see that the original steel bolts fail in the environment they live. I can't be certain that I will be able to keep the area dry and feel that I probably won't be able to accomplish that. The idea you have of allowing a means for drainage seems like a common sense approach. I will check further on the dissimulator metals factor. I think that a zinc coated grade 8 bolt might be the comprise.
How about titanium? corrosion resistance? Titanium vs iron dissimilar metal problems any better than SS?
Do the use of NYLOCKS effect the torgue values, or is this more of a feel your way there and common sense measurement than a precision calibration?

I remember when the "hot ticket" was Zeibart and Rusty Jones for rust proofing your car. I also witnessed countless cars here in the Midwest that rusted to pieces because the rust proofing trapped moisture and sealed drainage areas. I don't take the Foretravel out in Winter but I do take it in the rain. I don't want to compound the problem and make it worse by trapping moisture in the box beam area. Rusted, busted bolts are one thing, rusted out frame or box beams is another as Don has lived through. It would be easier in the future to replace the bolts than the beams.

The box beam; What is the actual size of it?
I want to buy 1/8" flat steel to stiffen the box beam but I'm not sure what width to order. I believe Brett mentioned 1 3/8" and another person suggested 1 1/4" (so the steel covers the entire side of the box beam shoulder to shoulder). Would a galvanized flat steel work sandwiched next to the iron beam?
Would a long length of steel against the box beam be better or worse (for drainage) than short sections that only cover the bolt/nut area?

Thanks again for all the great help!

Re: BULKHEAD repair parts checklist

Reply #10 – March 19, 2015, 10:23:55 am

Quote from: Lon and Cheryl – March 19, 2015, 03:28:22 am

I will check further on the dissimulator metals factor. I think that a zinc coated grade 8 bolt might be the comprise.
How about titanium? corrosion resistance? Titanium vs iron dissimilar metal problems any better than SS?
Do the use of NYLOCKS effect the torque values, or is this more of a feel your way there and common sense measurement than a precision calibration?

Stainless or plated steel will be light years better than the OEM. There are specially treated galvanized steel bolts that pass under salt water testing that would also work. See previous posts for manufacturer. No need for grade 8. Grade 8 will require increased torque to secure them and could distort the rectangular tube. The OEM Roloks were grade 5. I would think more than twice before I took all the bolts off at one time. unless you are really set up to do it. It's very easy to force the angle iron away and clean behind it with a Sawzall doing 6 or 7 at a time. If you have a compressor, Harbor Freight has fairly inexpensive sandblasters to make it super clean. Spray galvanize followed by a good rust restive paint will do the job. Driving in winter in a state that salts their roads will shorten the life of any RV. It gets everywhere. With the iffy Foretravel placement of some electrical panels, other damage will occur. That's why some members have moved them up to the area where the transfer switch and other electrics are. RVs with corrosion damage underneath are worth significantly less than clean ones.

Torqued the same with the nylocks. As you said, just a common sense backup.

Pierce

Re: BULKHEAD repair parts checklist

Reply #11 – March 19, 2015, 11:36:16 am

Lon,
For manipulating the gap at the joint, I used one or 2 bottle jacks in front of the drive wheels next to the air springs. This is in conjunction with having the safety stands in place behind the drive wheel. In other words to open the gap, raise the ram so that it is pushing down on the front of the "H" frame causing the control arms to pull the gap apart. Obviously this should be done with great care not to over do it. The fender trim screws should first be removed from the bulkhead side of the wheel wells so as not to crack the fiberglass. If there is a propane water heater on the passenger side against the bulkhead partition, there is probably one or two Rolok screws going into the the water heater frame from behind (in front of the passenger side drive wheel) which should be backed out so that the water heater frame isn't affected by the bulkhead gap opening. Of course, the tanks should all be empty when doing this work.
To close the gap, simply slowly release the ram on the bottle jack and the pressure from the rear safety stand will push down on the back of the "H" frame and cause the control arms to push on the rear angle iron to close the gap (depending on how well your coach holds air pressure in the leveling system, you made need to dump more air from the sir springs via the HWH control panel). if the air springs are in alignment and all are holding pressure, there is no force pushing or pulling on the bulkhead joint, though the angle iron may have taking a set bowing to the rear slightly. This will respond to the clamping force of the fasteners however, and flatten out as you torque them. Hopefully clear enough, but if not you can PM me and we can talk on the phone if you want...
Don

Quote from: Lon and Cheryl – March 19, 2015, 03:28:22 am

DON: I jacked the coach in the rear from the axle I can't remember exactly, but I think I did place jack stands in front of the axle to give me more room to work around the wheel. I will try your "stand placement behind the axle" when I want to draw the bulkheads together. Maybe ahead of the axle if I want to separate the bulkheads a bit to clean and treat the steel.

Re: BULKHEAD repair parts checklist

Reply #12 – March 19, 2015, 12:06:03 pm

When bolts are grade 5 or grade 8 you are dealing with tensile strength. Thread form, being it class "A", class "B", "C", etc, deal with thread form/depth of thread, amount of thread engagement between a male and female thread form of the same class.
You would be further ahead to consider the coating used on the bolt and/or the tensile strength of the bolt. A fine thread as opposed to a coarse thread provides more thread to thread contact when using the same diameter bolt.
I personally (even tho I do not have your type of coach) would use a 3/8-24 TPI bolt, either corrosion resistant coating, or use a Stainless Steel mat'l. Verify the tensile strength of the SS as there can be a considerable difference between 303 and 304 Stainless, for example.
Stainless Steel is a generic name for a class of mat'l that is manufactured in different characteristics for different applications.

Re: BULKHEAD repair parts checklist

Reply #13 – March 19, 2015, 12:34:05 pm

The structural transverse box beam is 11 gauge (⅛"wall thickness) 1.5" rectangular tubing. As far as sizing the stock for the backing plate, it depends on how straight you manage to drill the holes and whether or not the holes are centered in the box beam. Options;
1. You could make them out of 1.5" flat stock (I would use ¼" or at least 3/16" flat stock) with a ⅜" hole drilled in the center of it and then if the flat stock overhangs the bottom edge, enlarge the hole until it is flush and add a ⅛" thick regular washer to cover the gap around the bolt.
2. Or you could drill your hole through the angle iron and box beam, then clamp the piece of flat stock to the box beam to start drilling the hole in it guided by the hole you already drilled through the angle and box beam. once you have got the hole started, remove the clamps and put the flat stock in a vice to complete drilling the hole through it.
3. (not as good, but adequate) Use 1.25" flat stock with the hole drilled in the center.

Note that the ⅛" thick walled square tubing is only used in the bulkhead joints. The rest of it looks like it is 16 gauge (1/16"), but I have seen a parts list that indicated it may only be 18 gauge. Also, on the passenger side, there is about an 18" (at least in our coach) piece of square tubing doubled up behind the main transverse box beam that provides attachment for the angle iron. This short piece of tubing, is of thinner stock and is usually butted up against plywood that Foretravel uses in place of the blue styrofoam sheet in the to provide attachment points for things like hose reels. this complicates the repair a bit as it requires longer bolts and you have to chisel away some wood after you use a hole saw to create an opening for the backing plate and nut.
Edit to add picture of the framing.

Quote from: Lon and Cheryl – March 19, 2015, 03:28:22 am

The box beam; What is the actual size of it?
I want to buy 1/8" flat steel to stiffen the box beam but I'm not sure what width to order. I believe Brett mentioned 1 3/8" and another person suggested 1 1/4" (so the steel covers the entire side of the box beam shoulder to shoulder). Would a galvanized flat steel work sandwiched next to the iron beam?
Would a long length of steel against the box beam be better or worse (for drainage) than short sections that only cover the bolt/nut area?
Thanks again for all the great help!

Re: BULKHEAD repair parts checklist

Reply #14 – March 19, 2015, 12:56:44 pm

ARP-623 series bolts
Here are the fasteners that I chose for my bulkhead repair. They are stronger than grade 8, expensive, won't corrode, but there are other good stainless options that are equivalent to grade 5 bolts. I doubled up on the transverse tubing and so needed longer bolts than you will likely need. Here is a picture of some of the ones I used.
Don

Re: BULKHEAD repair parts checklist

Reply #15 – March 19, 2015, 01:07:37 pm

Fastenal stores are fairly situated throughout the US. I would try them and discuss what you are doing and your concerns with someone there that is not just a sales clerk, if you don't want to order online.

Re: BULKHEAD repair parts checklist

Reply #16 – March 19, 2015, 01:55:32 pm

About a buck each at: 316 Stainless Steel Hex Cap Screw Bolt PT UNC 3 8 16 x 3 1 2 Qty 25 | eBay free shipping no tax. Order 50 to double up. Use Milwaukee Hole Shooter with pilot hole first. 90 degree drill for the tighter stuff. I lube the bit several times on each hole.

Pierce

Re: BULKHEAD repair parts checklist

Reply #17 – March 19, 2015, 08:38:42 pm

I can attest to Don's gap opening method. I normally use 4 safety stands next to each air bag on the rear axle - each 11.5" long. I replaced the two forward stands with hydraulic bottle jacks and set them up so the fully compressed height was 11.5" tall. By
"set up" I mean adjusting the saddle screw and a riser block. I found that about 1/2" inch of displacement on each jack produced about a 1/4" separation at the bulkhead joint. When parked on level ground my bulkhead joint is normally under compression but I suppose that might differ from coach to coach depending on the engine weight, length and other loads on the structure. If guessing, I would say your joint is probably in compression too with the M11 engine and 4000 transmission loading down the back end. Lateral tubing that the Rolocks thread into is as Don said (1-1/2" x 1-1/2" x .120"). I found all other tubing is 18 gauge (.049") on my coach.

Re: BULKHEAD repair parts checklist

Reply #18 – March 19, 2015, 11:34:58 pm

Thanks John... I prefer to think of it as my "gap control method"

another thing I should mention about this process. If you haven't had a separation before doing this, then be extremely careful when attempting to separate the bulkhead joint. On our coach, it had already separated (not a singal bolt was doing its job to hold the joint together. I puzzled over how there could have been this separation without transmitting up to the sidewalls above the bullhead joint. One day while working under there, I found my answer: the bulkhead was hinging right at the intersection of the floor above the utility bay. Once the Roloks go, the only thing resisting the pull of the control arms when the rear suspension is moving is (at least on the coaches of the same length and vintage as ours), is 4 vertical pieces of 2"X2"X1/4" angle iron next to where the control arm shackles attach to. On our coach, they were all 4 cracked right at the top of the bulkhead below the floor above. The fenders, being a bit flexible, were able to move a bit with the bulkhead joint. The walls above were untouched (for which I was and still am extremely grateful!). So all this is to say, if the bulkhead joint hasn't seperated or moved enough to crack those vertical angle irons so that the entire bulkhead will hinge there, be extremely careful when using this technique (or any technique for that matter) to separate the joint for clean out. The cracks, if they are there, are no big deal if the bulkhead joint is sound. Those angle irons will still stiffen the bulkhead joint against the tanks which likely their primary function. In my case, I decided to weld the cracked angle irons and also welded in a three by five inch ¼" or 3/16" thick rectangular tubing in between each set of the angles and also welded some gussets between the added tubing and the engine carrier above. I have posted pictures of that (not sure, but maybe "bulkhead reinforcement"?), but not sure how to add them to this post from my iPad.
Edit: found a thread with pictures of what I described above
Bulkhead Separation - Planning for the Worst
Don

Quote from: JohnFitz – March 19, 2015, 08:38:42 pm

I can attest to Don's gap opening method.

Re: BULKHEAD repair parts checklist

Reply #19 – March 20, 2015, 02:38:23 am

THANKS for all the time you all have spent advising me on this repair. You have shed plenty of light on the repair, this will make my job MUCH easier!
And, SO MUCH FUN!

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