Body Repairs - General Guidance

Details

Written by Malcolm Eades

Like most of its contemporaries, the Z Magnette is prone to rust in certain areas of its body. Unfortunately because of its unitary construction (without a separate chassis) any corrosion of the lower body is likely to have structural significance and must be rectified properly if the car is to pass its technical inspection.

 The main problem areas are:

•  Inner sills, including reinforcing panel between the inner & outer
• Rear spring hangers
• Outer sill and the area behind the splash plates in the front wings
• Floors, especially under the double skin in the front footwells
• Wheel arch edges, especially rear, where there is a double-skin joint
• Door & wing bottoms
• Front wing top joint and around headlights
• Boot floor and spare wheel well

 Fortunately it is possible to obtain good quality repair panels and sections which, in some cases, are improvements over the original design. 

Before attempting any major body repairs, it is a good idea to take extensive measurements and photographs, so that you have something to refer to once the corrosion has been cut out. Also, if you are proposing to cut away a lot of metal in the sill area, you need to ensure that the car is well supported so that it cannot sag when its structural strength has been removed. It is a good idea to weld a bar temporarily across the door openings to preserve this key dimension; the quality of the door gaps will be a key indicator of the quality of the restoration.

It is possible to obtain frames that allow a stripped out body shell to be rolled on its side, so as to make working on the floor safer and easier. Members who have used these generally recommend them and for a total rebuild the additional expense is justified by quicker, better work.

If you are fabricating repair sections from sheet steel, it is best to use the same thickness as the original. Sheet is measured in “SWG” or Standard Wire Gauge, the lower the gauge number, the thicker the sheet. In cars, 18 or 20 gauge is commonly used but 16 gauge was also used in the Magnette. Workshop gauges to check thickness can be bought from tool suppliers.

There is a product called Zintec, which is steel sheet with a thin zinc coating intended to protect it against corrosion in storage. This may seem a sensible choice but in practice the coating tends to cause a lot of sputtering during welding and welders dislike using it.

Most of the body structure is held together with spot welds, which act like stitches between adjoining panels. To remove corroded panels, the best solution is to drill through the spot welds. Special drill bits can be obtained for this purpose. Just drill through the top panel, so that it comes away cleanly. Then the panel underneath can be cleaned up with a grinder, ready to receive the repair panel.

The body was originally assembled in sub-sections that were joined together on the production jigs to create the finished body. If you understand that assembly process it can often help you find the lines of spot welds that need removing. There is a factory manual called “Monocoque Construction in the MG Magnette” and this was produced as an explanatory introduction for dealers and repairers who would not have been familiar with this new production method. If you can obtain a copy or a digital reproduction it provides useful additional information beyond what is covered in the workshop manual, though the exploded drawings in the workshop manual are a good start point.

If you are letting in a repair section, such as a door or wing bottom, you have the choice of using a butt joint or “joggling” the panel, so that the joint is overlapped. If you can develop the welding skills to do a neat job, then the butt joint avoids possible problems from moisture entering a lapped joint later. When welding long joints, do it in small separated runs and progressively fill in the gaps until you have a complete joint. Do not let the panel over-heat or it will distort and be difficult to get back to the original profile.

Part of the production process involved lead loading. This was a normal way of creating a smooth surface over joints or low spots and involved “tinning” the metal of the body shell by flowing solder onto it, to give the lead a good surface to adhere to. Lead was then softened to a malleable consistency using heat and moulded onto the tinned area using wooden paddles and a lubricant. On the Magnette there is an area on top of each of the rear wings behind the window opening where lead loading was uses to conceal a welded joint. It is possible that during welding you may disturb leaded joints, which will need re-leading. Or you may want to use this process to finish the repair joints that you make. Tools and materials are readily available for this though for the amateur it make take a bit of practice to get it right. If the lead is over-heated it will simply flow straight onto the floor!