Permatex Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker

Permatex Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker (81878) is a single-component, high-temperature room-temperature vulcanizing (RTV) silicone formulated for high-heat powersports exhaust junctions and engine sealing applications. Standard black or grey RTV silicones break down, harden, and lose adhesion when exposed to sustained exhaust header temperatures, leading to exhaust gas leaks, unburned two-stroke oil ("spooge") seepage, and false air intake near oxygen sensors.

Engineered with a metallic-copper oxime silicone formula, Ultra Copper withstands continuous operating temperatures up to 600°F (316°C) and intermittent thermal spikes up to 700°F (371°C).It cures upon exposure to atmospheric moisture into a flexible, non-corrosive rubber seal that offers three times the oil resistance of conventional silicones and eight times the flexibility of cut paper or cork gaskets. The neutral-cure, low-odor paste is 100% sensor-safe—preventing oxygen sensor fouling and aluminum flange corrosion—and fills surface gaps up to 0.25 inches (6 mm) across rigid or stamped metal assemblies.

Features:

• 700°F Intermittent Thermal Rating:Handles continuous temperatures from -65°F to 600°F (-54°C to 316°C) and intermittent peaks up to 700°F (371°C) without cracking, shrinking, or hardening.

• Enhanced Oil & Fluid Resistance:Delivers three times greater resistance to synthetic and conventional motor oils, gear lubes, and glycol coolants compared to standard RTV silicones.

• Sensor-Safe, Non-Corrosive Oxime Chemistry:Neutral-cure formulation will not foul oxygen (O2) sensors, damage catalytic converters, or corrode cast aluminum and magnesium flanges.

• High Elasticity & Vibration Absorption: Eight times more flexible than traditional cut gaskets, maintaining a seal across dissimilar metals experiencing heavy vibration and thermal expansion.

• 0.25-Inch Gap-Filling Capacity: Non-sag metallic copper paste bridges surface imperfections and fills flange clearances up to 1/4 inch (6 mm).

• Dual-Purpose Gasket Maker or Dressing:Functions either as a standalone form-in-place gasket or as a high-temperature sealant dressing on pre-cut exhaust and engine gaskets.

What's in the Box:

• 1x Permatex Ultra Copper® Maximum Temperature RTV Silicone Gasket Maker 3 oz (85 g) Squeeze Tube (Part #81878)

• 1x Tapered Cut-to-Size Applicator Nozzle with Screw Cap

Application & Compatibility:

• Primary Powersports Uses: 2-stroke exhaust pipe manifold spigots and O-ring grooves, 4-stroke header-to-cylinder head flanges, slip-fit exhaust mid-pipe joints, turbocharger/supercharger flanges, valve covers, oil pans, timing covers, water pump housings, and thermostat housings.

• Substrate Compatibility: Cast aluminum, billet aluminum, magnesium, stainless steel, mild steel, cast iron, and titanium flanges.

• Fluids Resisted:Synthetic and petroleum engine oils, 2-stroke transmission oils, gear lubricants, automatic transmission fluid (ATF), and ethylene glycol/water coolants.

• Limitation Warning:Not recommended for use as a cylinder head gasket or on components in continuous direct contact with liquid gasoline (such as carburetor float bowls or fuel tank petcocks).

• 2-Stroke Exhaust Spigot & O-Ring Sealing (Stopping "Spooge"): On 2-stroke dirt bikes, the junction where the expansion chamber slides over the cylinder exhaust flange is a primary source of unburned oil leaks and air leaks that lean out jetting. Clean the cylinder spigot and pipe collar thoroughly with brake cleaner or contact cleaner. Install fresh Viton exhaust O-rings into the pipe grooves, then coat the O-rings and the inside of the pipe collar with a thin film of Permatex Ultra Copper before sliding the pipe onto the cylinder. The copper RTV lubricates the O-rings during assembly so they do not pinch or roll, while curing into a 700°F thermal barrier that stops black oil drips down the front of the engine cases.

• 1. Clean both mating surfaces with a residue-free solvent and let dry completely.

  2. Cut the applicator nozzle to lay down a continuous 1/16" to 1/8" bead along one surface, encircling all bolt holes.

  3. Assemble the parts immediately while the silicone is wet and tighten the fastenersfinger-tight until the silicone just begins to squeeze out evenly around the flange perimeter.

  4. Allow the silicone to set and skin over for1 to 2 hours, then torque the fasteners an additional 1/4 to 1/2 turn to final factory torque specifications. Allow a full24 hours before exposing the joint to high-pressure oil or sustained high-heat exhaust loads.

     The Two-Step RTV Torque Procedure (Do Not Over-Compress Wet Silicone): Unlike instant 1-minute gasket makers, traditional moisture-curing RTV silicones require a two-stage tightening sequence so you do not squeeze all the sealant out of the joint while it is wet:

• Exhaust Slip-Joint Assembly: When installing aftermarket 4-stroke slip-on mufflers or full exhaust systems that lack graphite crush gaskets at the mid-pipe junction, apply a light, even coat of Ultra Copper to the inside female sleeve before sliding the pipes together. Wipe away any excess squeeze-out with a dry shop towel immediately before it skins over. This prevents deceleration popping caused by air being drawn into the mid-pipe joint and keeps pipes from seizing together due to galvanic corrosion.

• Preventing Tube Curing Between Uses: Moisture in the air triggers the vulcanization process in oxime silicones. When finished dispensing, squeeze a small 1/4-inch tail of copper paste out past the tip of the plastic nozzle and thread the cap back on.That exposed tip will cure into a solid rubber plug that seals the remaining paste inside the aluminum tube from ambient humidity. Before your next project, pull the cured plug out of the nozzle with needle-nose pliers.

Part Number: 81878