Chicagoland MG Club: Tech Tips

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The Basics of Rust Repair

The most feared four letter word in a British sports car owner's vocabulary must be rust. I once saw a TR250 collapse in the middle when lifted by a tow truck; when set back on all fours, the center portion of the frame was resting on the pavement. Rust, caused by road salt and neglect, was responsible.

Even in areas where road salt is not used, rusting agents may be present which literally eat holes in automobiles. Dilute sulfuric acid is present in many areas in the highly publicized form of "acid rain". Some crop spraying chemicals are also active rusting agents, while salt spray in coastal areas often turns cars into dangerous hulks of rusty steel lace. Once the rusting process has begun (often by the time the car reaches the dealer), it is too late for protection ­ remedial action must be taken immediately to remove existing rust, no matter how seemingly insignificant.

The only way to remove rust which hasn't yet eaten entirely through its "host" panel is to sand down to clean metal, treat the sanded area with a rust remover (most proprietary solutions containing phosphoric acid work well), wash thoroughly to remove all traces of the rust remover, prime and paint. It's a lot of work, even for a relatively small area. If rust is forming between two pieces of metal spot-welded together, or otherwise lapped over each other, acid treatment is not recommended, as it can't be adequately neutralized.

What can be done to de-rust a sealed, boxed-in area? Unless you can get to all rust-contaminated surfaces and de-rust them, there's not much that can be done. Generally, the compounds advertised as "rust neutralizers" and such, have some rust retardant value, but they don't seem to effect permanent cures. "Body cancer" is one of the least pleasing pseudonyms of automotive rust, but one of the most accurate. Once rust has eaten through a panel, even in pin-holes, the only cure is to cut out the affected part and weld in a new piece. This can be more trouble and certainly more expensive than prevention or immediate first aid when rust is first noticed, but it is the only way to cure the problem. Body-putty, lead, pop-riveted patches and other commonly used "repair" methods only hide the problem, they do not cure it. Rust has an even more dangerous cousin, the electrolytic corrosion of aluminum panels where they join steel, as on Big Healeys. In this case, the aluminum and steel, in the presence of moisture, act as an electric battery, especially when the moisture is salt-laden and the temperature is warm. When this occurs, the aluminum crumbles and turns into white powder, leaving the steel rusty, but usually sound. What makes this form of 'body rot' worse than rust is that it is much more difficult to perform 'cut and weld' repairs on aluminum than on steel. Prevention of corrosion is much easier than repair. When washing your car, wash it thoroughly underneath as well. Do whatever you can to dry it - blow with compressed air, mop it dry, or open doors, trunk and hood to allow water to evaporate. Letting it sit out in the hot sun will dry it quickly enough. Above all, do not put a wet car in a heated garage; heat, combined with high humidity, is what rust thrives on. Check the car thoroughly underneath for raw or rusty metal areas. Clean and protect them with paint, undercoating, or even grease. Have you ever noticed that the bottoms of your front floors never seem to get rusty, the oil from engine leaks protects them. (This won't prevent floors from rusting from the inside, though.) Do whatever you can to prevent rust from starting. Most commercial undercoatings work very well when properly applied. Checking a car for rust and finding all the rust is not as easy as it sounds. For example, by the time rust bubbles appear under the point at the lower front of MGB rear fenders, it' s a good bet that at least the rear portion of the rocker panel (covered by the fender) and the vertical inner sill panel are in much worse condition.

The only way to find this dangerous structural rust is to explore. Remove the outer rusted fender section, probe deeply and try not to be horrified by what is found. On most cars, removal of the front bulkhead sealer plates will show if there is any rust "inside" the lower rear of the front fenders. This is one of rust's favorite spots. While exploring, the traditional "ice pick" method works, but I prefer to tap suspect areas with a body pick hammer which has the pick ground to a hemisphere about l/8" in diameter. Light tapping with this won't damage sound bodywork, but it will, by sound and feel, if not by penetration, find all rust damaged areas which are not usually apparent. So your car's like mine, well past the prevention stage, and ready for major surgery. Moss helps hundreds of us each year by supplying not only complete fenders, rocker panels, and floor boards, but also repair panels which are designed to replace those areas of your car which are prone to rusting. Check the Moss catalog for the car of your choice and you will likely be surprised by the number of such body repair pieces available.

A close-up of true evil: rust! Do whatever you can to prevent rust from starting. Checking a car for rust and finding all the rust is not as easy as it sounds.By the time rust bubbles appear it's a good bet that at least a portion of the panel is in much worse condition.

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