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MG MGA - heat shield

Should the heat shield be painted on both sides, with the engine colour?
Nigel Munford

Mine is painted engine colour on both sides. 1957 Mga Coupe

Gordon
Gordon Harrison

Nigel

Technically you need a reflective surface finish as well as an air convection type barrier.

New shields I've seen are sold as plated, probably zinc with clear passivation. Would seem the ideal.

Paint would not be very effective at reflecting and may even blister with the exhaust manifold heat.

All wrong I know, but on my recent engine rebuild, I actually painted my now rather rusty and cracked shield (must get a new one)with a matt black paint, I think is called "Pot Black" or similar, which the motor bike fraternity use - it looks OK. After brushing on, you let it 'dry-off' and the hot bike cylinder head should complete the stoving off. I put it in the wife's oven for 20 mins and that does it!

I also use this stuff on the brake drums as they get hot too. No more bistering now... HTH

Pete
Pete Tipping

Mine is origional to my car and the back side has two pieces of of thick woven fabric riveted to it. There is an opening vertically in the middle. The metal is apinted engine maroon. Gordon
Gordon Harrison

Hi Nigel. Heat shields need to reflect heat as mentioned above. However, most old heat shields deteriorate, rust or discolour. This often results in engine vapour lock problems due to heat absorption and retention around the carburettors. My MGA 1500 had a very bad case of vapour lock in summer weather driving conditions. I fabricated a new heat shield out of sheet stainless steel, and the vapour lock problem vanished entirely! Making a new heat shield out of sheet stainless steel is quite easy. The few bends can be done over the edge of a workbench with a hammer. The only "special" tool required is a suitably sized hole saw, to cut holes for the carburettor air intakes. I re used the asbestos insulation from my old heat shield, although there are better, safer modern materials that would be as thermally efficient. Additionally, the polished stainless steel, although non stock, looks very attractive under the bonnet. Cheers, Glenn
Glenn

Glenn
How did the vapour lock manifest itself? I ask as I have just rebuilt my SUs, and the car is now misfiring when it gets really hot (here in Malaysia, that is easily done!). The heat shield on mine (1957 roadster) is original (silver painted or plated/rusty, with asbestos pads on the back).

thanks

Andy Drinkwater
A R S Drinkwater

Well, my 1500 went for years without a heat shield and it seemed to run okay. I don't know whether it still had one when my dad bought it in '63, I think I asked him once but I don't remember his answer. However, I did buy a new one from Moss a few years ago and will be installing it when I put the car back together.
Del Rawlins

Hi Del Was that car driven in Alaska or someplace relatively cool? Here in Ontario Canada, summer temperatures often reach 90F, 100F, or sometimes substantially hotter! These extremely high temperatures promote vapour lock. Underhood temperatures soar. In these conditions a proper heat shield can make the difference between vapour locking or not. Cheers, Glenn
Glenn

Yes, my MGA has been a pacific northwest car its whole life. Dad bought it in Seattle, and it stayed in western Washington until '79, when we moved to Alaska, and it's been here ever since. Oddly enough, my dad said that it just happened to be shipped up in the same container with a yellow MGA coupe.
Del Rawlins

This thread was discussed between 15/11/2006 and 19/11/2006

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