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I was reading some discussion recently about the concern of moisture inside the chassis tubing leading to rust, and using an inert gas to help prevent it.

I'm not *too* concerned w/this, but I had a thought & wanted to look for opinions: I've heard of using expanding polyurethane foam(similar to the cans of window insulation stuff)in unibody cars to help stiffen the door sills & other hollow sections. I wonder how practical/beneficial it would be on a Locost?

We don't really *need* much of an increase in chassis strength....but then again, if it would happen to prevent/diminish rust w/o adding any real weight, it may be worth while looking into it.

The foam stuff would work really well. Another thing you could use is Waxoyl or "fish oil". The only problem with the foam is that if you do have to weld to the steel again, it'll melt the stuff inside the steel.

If you can weld up the tubes to seal the ends, you dont need to use any gas. The air that will be contained will never increase in moisture content, and any moisture that is in the air will probably oxidize the steel pretty fast and will then be "used up," persay.

Thanks!

I'd heard of the "fish oil" but I thought I had to be applied w/the correct sprayer & nozzel to get good coverage. I didn't know that a sealed tube wouldn't continue to rust indefinately...I may just go that route.

I used and old air plane method slightly modified. Use linseed oil coating on the inside surface of each tube. I made what looks like a long rifle cleaning rod and made a mixture of linseed oil and bee wax cut with turpentine. It takes several weeks for the mixture to set up, but forms a very nice sealed surface. If you do weld, some of the wax will melt and help re-seal the heated area. I coated most of my tubes before I welded them, a few you can do after welding. The foam idea sound pretty good, think that you would probably have to drill two holes to help with the filling process. Anybody actually weld a foam filled tube and afterwards cut it open to see how well it still covers? Dave W

Careful with the foam idea - some of them are flamable. You'll also have a problem with getting foam through the entire tube, as mentioned earlier. Plus, the stuff stinks and smokes heavily as it melts from the weld. I used some self-extinguishing rigid foam in the trucks I built, but didn't want to risk it with the foam-in-a-can. The fumes were what really worried me most. As long as the tube you use was kept dry and is rust-free to start with, if you have good welds you shouldn't have any problem. At most I'd try the oil/wax in the tube.

Another option: cap one end of each tube, get a gallon of Rust-oleum and pour it into each tube to cover all interior surfaces. Pour out the excess and allow to dry. The welded areas will burn away during the welding process, but the majority of the tube interior will be fine.

The onlyarea I see that should be a potential problem is where you end up drilling into the tube for rivets. I'm no fan of rivet holes on exterior surfaces, but considering the typical Locost gets little use during wet weather this may not be that big of an issue. Either way, I'd take a few extra steps to make sure moisture doesn't get in around the rivet.

What about just taking it to Ziebart and having them spray their waxy crap in your tubes?

If you use a polyurethane foam you do indeed need to be careful when welding it. When it burns it gives off a little something called hydrogen cyanide. Probably not a good idea without good ventilation.

I think another solution is to consider that your car is not going to last forever. If you still are using it 15 years later, consider building a new frame at that time and transporting everything over to it.

FWIW, you do drill into the chassis tubes to attach aluminum panels, so those are not 100% sealed like you might think welding onto the end.

I think we have to worry about corosion from stuff getting traped inbetween the aluminm or steel panesl attached to the tubes more than anything. I think if you seal that surface and clean and maintain them, you have done the most that would be needed towards preventing rust IMHO.

if you are really worried about rust.. try POR-15. that stuff is supposed to work very well.

http://www.por15.com/

The ultimate solution is to move to the desert southwest.. I have steel that has been sitting outside uncovered for a year and its still not rusty.

bare metal develops a surface patina here and thats it. Its too dry for metal to rust.

Lol...thanks for the tips!

I was planing on doing the outside of the chassis in POR-15, hadn't thought about trying to coat the inside w/it though.

And yeah, I really like the desert S/W. I'd love to live out there if I survive until retirement.

For the interior of the tubes you might consider using fuel tank sloshing compound, though I would think it would be a large PITA. I plan on using 14 gauge steel on the firewall, floor, rear bulkhead, and tunnel sides with the sides skinned in 22 gauge steel for additional chassis strength. What I plan on doing to seal and since it would glue the sheet to the tubing is a light coat of Linex. I was telling this to a friend and he knew of a dirt tracker who had his car done with linex and weighed it afterword, it had gained 20 lb where normaly if he used paint it gained 45 lb. This would work well on the inside of an aluminum sided car as well.

When I built the frame for my teardrop trailer, I too was concerned with rust on the inside of the tubes.

I once had a car hauling trailer that spent two years in the Florida Keys, five feet above sea level. Although the epoxy paint was unblemished, the interior steel was nearly all gone. Thing collapsed 100 miles into a 1500 mile move!

This time, I had the bright idea of putting oil inside the tubes. I welded on a threaded coupling for a pipe plug, stuck in a funnel and filled away, using every half full bottle on the shelf: gear lube, ten year old Bel Ray premix, chain lube, chainsaw bar oil, ATF, power steering fluid, whatever.

Evidently I'm way too confident in my welds, they look good, hold up fine, but just don't seem to be waterproof. I'm still leaving signature puddles everywhere I visit

Lenny

What you could do is drill a hole at every joint, hook a pressure gauge to the chassis, then fill with inert gas. If the pressure gauge drops you've developed a crack.

Interesting idea but unrealistic, unless the whole chassis had open joints which made it so you filled the chassis and only needed one gauge to monitor the pressure, you could even put the gauge in the cabin area so you can always keep an eye on it.

drill a 1/8" hole in the solid tube where there is a joint.
it would make the chassis a single chamber, fill it with helium for weight reduction.

the pressureised gas method won't work if your floor is rivited though.