Re: My bulkhead experience
Reply #45 –
Here is what I found out when repairing my bulkheads on my 96 36' U270. First the joints had no separation and only a little rust on the metal angle which I wire brushed off. I found 4 bolts on the rear bulkhead that were broken at the usual 3 or 4 threads from the head. Three were at the passenger side end and one about 6 bolts in from the right side on the rear. The front bulkhead had 2 bolts broken at the end of the angle on the passenger side. I decided not to remove any of the bolts that passed the torque test, but a couple of bolts did back out with the torque test, so I removed them and replaced with 3/8" grade 8 bolts. Most of the others I drilled a new hole alongside the broken bolt. I also installed new bolts in between every 2nd and 3rd bolt that was not broken. I made 1 1/4 x 1 1/4 x 1/8 backing plates for the locking nuts. There was one place where I used the double nut procedure to remove a broken bolt. That was difficult as it was well rusted and required an overnight application of rust buster. I really needed to get that one out as it was near the end of the angle and the only spot for a replacement. In another post I mentioned that I had some 1 1/2 x 3" tubing in the frame of the basement floor behind front angle. That was not the case as I found out when drilling for new bolts. It really was 2 pieces of 1 1/2 tubing back to back. It did not extend all the way to the ends but almost. I had to use 4" long bolts where it was doubled. I also found a short section at the rear with doubled 1 1/2 on the drivers side at the utility compartment. Most of the bottom panel at the rear just had one piece of 1 1/2, so 3" bolts for that. I'm not sure why there is 2 pieces at the front unless it is extra support for the large propane tank. At the ends of the angle the original bolt went into the hollow part of the metal tube that runs fore and aft down the sides. All I could do was install a new bolt inboard a little beside that tube. I also predrilled a piece of hardwood (maple) on a drill press to use as a guide in drilling the new holes. I had to shape it a little as metal angle is not exactly 90 degrees on the inside. I clamped it vertically to the angle where I wanted a new hole. Had to wing it in a couple of places where something was in the way and I couldn't use the guide.
Before I started any of this, I cleaned and lightly sanded the fiberglass skin near the bulkheads with the intention of re-fiberglassing the holes that have to be made for the nuts. I drilled a couple of holes with a hole saw and didn't like it for fear of penetrating a tank. I switched to a Rotozip tool and made small rectangular holes in the fiberglass skin. That worked well as the bit isn't long enough to go through the upper skin. I used a small long 1/4" diameter magnet to locate the metal behind the fiberglass. I could go right up to the metal with the rotozip if needed and around any of the protruding old bolts. I found a couple of places at the rear bulkhead where there was a piece of 3/4" thick plywood in addition to the foam. One was at the right side where the water pump and pressure tank are located. I think it is there for bolting down the water pump. It had been wet but was not rotten. The rotozip made it easy to remove enough plywood for the nut and bolt. I had to go slow though so as not to break the bit. The other piece of plywood was under the utility storage area next to the fresh water tank with nothing bolted to it and it was like new. After the bolts were in I foamed the cavity around the nuts. I haven't done the fiberglassing yet, waiting for good weather and time permitting.
Most of the broken bolts are at the curb side, Maybe water runs to that side because the curb side is usually lower. Also the fresh water tank overflow is on that side at the rear. I plan to undercoat the angle and spray the joint next to the angle with Corrosion X HD once a year. Also maybe relocate/or extend the fresh water tank overflow.
Think about this, the basement compartments seem to be built like a deep one shelf bookcase with a plank at the top and bottom and 4 vertical planks in the middle with no lateral bracing. A bookcase would normally have a back made of plywood or solid wood for lateral bracing. In this case it seems like the only lateral support is from the metal at the ends which is part of the wheel suspension. I suppose the tanks could provide a little lateral support. There is a lot of weight down there if the tanks are full, along with the batteries, tools and all the other stuff we carry. When we step on the brakes it all wants to move forward or a little bit aft during acceleration. Maybe that is helping to break the bolts. I also notice that there is a row of these same bolts across the bottom at each of the inner bulkheads. I didn't do the torque test on them or notice any missing. My bolt man said that my bolts are not Rolok as Rolok has a trilob slightly spiral shape to the threads. The 2 unbroken ones I removed are round and threaded to the point on the end and are hardened. They will form threads when screwed into a softer metal such as mild steel.
I checked all the welds I could see for cracks and didn't find any, did find a leaking shock. Thanks to Brett Wolfe and all the others who provided advice about this problem.
Topic: My bulkhead experience