"Inside the MGB's Unit Body"
"Even by 1958 before the MGA 1600 had been put into production, Abingdon had had thoughts about a new model to replace the MGA. After one serious attempt to provide the existing MGA chassis with a completely new body (EX214), work began on a car with a completely new structure. By 1959 the MGB project - coded EX205 by Abingdon, ADO23 by BMC - was underway. Apart from its body shape, the MGB was also to be distinguished by its unit-construction body/chassis structure." (Graham Robson, The MGA, MGB and MGC, Motor Racing Publications Ltd., 1977)”
Our first tech session for 2019 explored the inner body structure of the MGB. "Unit-body cars rely on the combined strength of sheetmetal stampings for their structural rigidity. The vehicle's roof, floor, A-, B-, and C-pillars, the firewall, and the sills are all key components to the unit-body vehicle's skeleton." (Hemmings, July 2007) Our goal was to see how the unit body fits together and then note how corrosion (rust) becomes a special problem and note the more complex repairs that are required to properly restore such cars to original strength and appearance.
Club members gather at Artisan Autobody in Manassas Park, Virginia for a look inside the unit body of the MGB.
In the background is Jim Spurgeon's 1966 MGB GT which was the main subject of the session. In the foreground is a 1968 MGB GT which is just about ready for final body work and paint. This car had suffered collision damage in the left front which required some major straightening. This work is normally more complex on a unit body car than on a body-on-frame car. Coincidentally both cars will be re-painted in their original mineral blue.
Rust normally begins to form inside the rocker assembly. Lincoln Moore points to the jagged remnants of the plenum / inner membrane. Only after rust has developed here will you begin to see the paint bubbling up under the rust as it works its way from the inside out.
Our host, Kevin O'Grince shows us some of the tools which he uses in repairing body structure of MGBs. Kevin is a graduate of McPherson State College's degree program in automotive restoration which is the only one of its kind in the country. Jay Leno sits on the board and the program was featured on an episode of Wayne Carini's "Chasing Classic Cars" program.
Jim Spurgeon holds the rocker or outer sill to show that it extends under the rear "dog leg" and the front fender to tie the front and rear structures together. In front to the right is the lower sill or "castle rail" and to the left is the inner membrane. All these, joined to the inner sill, make a very strong box section which contributes to the very rigid structure and tight handling of the MGB.
Sometimes you need more than two hands! Jim Karcher examines the lower sill or "castle rail" surrounded by fellow members Bob Watkin, Scott Gibson and Barry Stoll.
Kevin O'Grince and Lincoln offer up the new lower sill / "castle rail" showing how it ties everything together underneath the rocker assembly.
The new rocker (outer sill) is held in front the remnants of the old one which will be completely removed to make way for the new one. The rear 13" will be covered by the rear body panel. The closeness of these panels provides a place where moisture and mud can accumulate and work on the metal from the inside.
Kevin O'Grince explains the vast improvements which have been made in paint and sealant technology since our cars were built. These improvements allow restorations to be, in some ways, much better than the cars were when they left Abingdon.
Bonus time! Kevin with assistant Fernando Aguilar demonstrate paint restoration techniques on a very strange looking "MG". Often great improvements can be made with careful work on old paint.
Mike McCormick took all the photos. Thanks Mike.