An Incredibly Easy Method That Works For All
10 Apr 2021
Repairing exhaust heat shields with rivets
Almost every car has them: thin aluminium or aluminised steel shields tucked between the exhaust and the things you would rather not cook, such as the fuel tank, brake pipes, wiring loom and floor pan. They are usually held on with spire clips, small flanged bolts, or a bracket with a crush washer, and none of those fixings enjoy the environment they live in. Heat cycling expands and contracts the metal dozens of times on a long journey, engine and road vibration works everything loose, and road salt quietly consumes whatever is left.
What usually happens is that one or two fixings fail first. The shield then hangs on the remaining fasteners, flaps in the airflow and buzzes at certain revs. Eventually a tab cracks, the bolt head rounds off, or the clip pulls through the thin metal altogether. Owners often simply remove the shield, which is a mistake on anything with a plastic fuel tank or a wiring run close to the exhaust. Riveting is often the neatest way to put it back, because a rivet spreads its load over a wider area than a small bolt and never needs access to the back of the panel.
You do not need much, but using the right consumables makes the difference between a repair that lasts five years and one that fails in a fortnight.
Work on a cold exhaust, on axle stands, with eye protection. Old underbody dirt and rust flakes make drilling unpleasant, so brush the area down first. If the shield is still attached at one end, support it with a bungee or a bit of wire rather than letting it hang on a brake pipe.
Drill out the old fixings rather than fighting them. Use a bit the same size as, or a fraction smaller than, the rivet body, and start with a centre punch so the bit does not skate across the thin metal. If a bolt has seized, drill the head off and punch the remains through. Once the shield is free, clean both mating faces with a wire brush and look for cracks radiating from the old holes. Stop-drill the end of any crack with a 3mm bit, otherwise it will keep travelling.
Keep the original air gap. Heat shields work by creating a still layer of air between the hot part and the panel, so do not pull the shield tight against the floor. A washer or two on the rivet, or a short piece of tube, will maintain the spacing and stop the rattle at the same time.
Where the mounting hole has torn or enlarged, do not simply fit a bigger rivet in the same raggy hole. Cut a small plate from scrap aluminium, about 30mm by 40mm, drill it to match and rivet it over the damaged area, then fasten the shield to the plate. Where the mounting point on the body has rotted away completely, drill a fresh 4.8mm hole in sound metal nearby and use a large-flange rivet there instead.
Think about the metals you are joining. Aluminium rivets into an aluminium shield are fine. Steel or stainless rivets into a steel bracket are strong, but mixing aluminium and steel in a wet area invites galvanic corrosion, so smear a little sealant or zinc paint over the joint afterwards. Near a catalytic converter or a turbo downpipe, heat is high enough that an aluminium rivet can soften, and a steel rivet is the better bet.
Once everything is secure, spray the repaired area with cavity wax or zinc-rich paint, including the rivet heads and any bare metal you exposed. Refit any plastic undertrays, then start the engine and listen for buzzes at idle and at around 2,000rpm, which is where loose shields usually announce themselves. A road test over a few rough surfaces will confirm it.
A securely fixed heat shield also keeps an MoT tester happy, since insecure or missing shields are regularly noted as advisories. Done with a handful of large-flange rivets and a bit of patience, this is a repair that costs pennies and can outlast the car. If you have a rivnut tool in the drawer, it is worth knowing that the same approach works beautifully where you want a threaded fixing back in thin sheet, but for heat shields a plain rivet is usually quicker, lighter and perfectly adequate.
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April 25, 2019 at 10:46 am
Take in the iconic skyline and visit the neighbourhood hangouts that you've only ever seen on TV. Take in the iconic skyline and visit the neighbourhood.
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Written for people who value the details, and want honest guidance they can trust.
Soldman Kell
April 25, 2019 at 10:46 am
Take in the iconic skyline and visit the neighbourhood hangouts that you've only ever seen on TV. Take in the iconic skyline and visit the neighbourhood.