The MGA With An Attitude

MGA exhaust system parts As noted in article EX-101, the flat rectangle near the center of the diagram is an insulated heat shield attached under the plywood floor. It is not intended to keep heat out of the cockpit, as the plywood floor and carpet padding do a reasonable job there (assuming you don't mind just a little heat in a light weight open roadster).

I have never found it necessary to put any heat insulation under the boards. The gap between the boards and exhaust pipe is originally about 3/4 inch. Hundreds of thousands of miles in service has not produced any sign of any scorching or discoloration of the wood or enamel paint. However, If the rear pipe hanger should fail, weight of the muffler can cause the pipe to bend down at the back and bow upward in the center (especially if the pipe is rusted enough to be rather thin). Then the pipe could touch the floor, so the heat shield is there to prevent burning the wood in this situation.

exhaust-floor heat shield
Click for full scale printable drawing - (74-KB pdf)

This heat shield does not appear in any factory documentation. I am inclined to concede that it may not have been factory supplied. It is available from Moss Motors Ltd., and I highly recommend that it should be installed for safety.

In cases where the heat shield is missing, some owners may not be aware that it should be there. If they happen to experience a burned floorboard they may get creative with other ways to protect the plywood as well as insulating the floor to suppress heat in the cockpit.

Here is an example from Jim Ferguson in North Carolina, USA, with a couple pieces of fiberglass cloth sandwiched between two aluminum sheets with a 1/8" spacer between them with pop-rivets. The shields were mounted to the floorboard with wood screws with another 1/8" spacer between the wood and shield. The exhaust clamp was later replaced with a strap type clamp to improve clearance from the shield.

  pipe shield
pipe shield
Picture above from Bill Haglan in Virginia, USA, shows a piece of curved steel sheet about 5-inches wide with edges folded for stiffening, welded to a couple of pipe clamps. This provides a shield with an air space between the pipe and sheet. This can reduce heating of the floor substantially by interrupting radiant energy and reflecting it downward, but the steel sheet could still get quite hot. The white piece above is simply white paint on the original floorboards. The original insulation lined steel heat shield plate is not shown here (normally screwed to the bottom side of the floor board directly under the seat). I have experienced problems with pipe clamp U-bolts hanging below the pipe and dragging on "high center" ground obstacles, so I would at least cut off the protruding threads.

If you want to reduce heat in the cockpit, here is one I particularly like.
On 08 December 2008, Andy Preston, in California, USA wrote:
floor shield >>"I manufactured heat shields from 6" wide x 1/8" thick aluminum sign blanks. I turned the edges down 3/4" for strength and attached them to the floor rails with 1 1/2" x 1/4" machine screws with countersunk heads. I split the distance between the exhaust and floorboard and used nuts and washers as spacers. Far easier on a restoration with no body on the frame but you could do the same thing through the floor boards at the frame supports."

For installation after complete assembly, these sheets could be attached from underneath with wood screws. Hex nuts would make good spacers, as the air gap doesn't need to be particularly large. Bare aluminum sheet can make a good radiant energy reflector as well as conductive heat barrier. If the rear pipe hanger should fail and cause the pipe to come into contact with the shield, resulting noise may be a good thing to alert the driver to the problem underneath.

On 3/7/2015, David Adams wrote:
"Here is another take on the exhaust heat shield. It is made from some scrap 6" stainless flue pipe cut into 3 segments 150mm wide and then turned up 12mm at the sides. The shields are attached through slots using stainless Jubilee clips and held off the pipe by saddles to give 5mm clearance. The saddles are attached to the shield with self tapping screws just visible at the attachment nearest the camera.
exhaust-pipe heat shield

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