Valve Covers, Valve Cover Breathers & Components

What Valve Cover Breathers Do

A valve cover breather gives your crankcase a controlled vent for pressure and a filtered path for fresh air. Every running engine pushes some combustion gas past the piston rings. That blow-by pressurizes the crankcase.

Without a vent, pressure finds the weakest seal. You'll see oil seeping from valve cover gaskets, the rear main seal or the dipstick tube. A crankcase breather relieves that pressure before it forces oil past your gaskets.

Most breathers use a filtered element, such as a foam screen or metal baffle. It keeps dirt out and catches oil mist before it escapes. The breather mounts in the valve cover, usually through a grommet, so it's one of the simplest ventilation parts you'll install.

Whether it's a stock rebuild or a race engine, you'll find the full ventilation setup here. This category is part of our engines and components department. Pair your breathers with engine dress-up kits for a matched finish.

How a Breather Differs From a PCV Setup

A PCV system actively pulls crankcase vapors out, while a breather passively lets filtered fresh air in. The PCV valve connects to manifold vacuum, which draws blow-by gases into the intake so the engine burns them. The breather on the other side replaces that volume with filtered air.

That's why the common setup runs a PCV valve or PCV breather in one valve cover and a filtered breather in the other. Two open breathers alone only release pressure as it builds, so vapors linger and oil mist collects in the filters.

Mr. Gasket chrome breathers come with or without a PCV hookup tube, so you can build both sides of the system from one product family. They use metal baffle and foam elements, fit a 1-1/4 in. hole and include a grommet. Before you buy, check which cover has the baffled opening and plan your hose route to the intake.

Types of Valve Cover Breathers and Mounting Styles

Pick a breather by how it mounts to your valve cover and whether it connects to a hose:

• Push-in breathers press into a grommet or oil baffle and pull out for service.
• Twist-on breathers turn into a matching valve cover opening.
• Clamp-on filter breathers mount to a tube or neck with a band clamp.
• PCV breathers hold a PCV valve and connect to manifold vacuum by hose.
• Hose-fitting and AN breathers use slip-on or AN ends for plumbed systems.

Billet Specialties breathers are machined from 6061-T6 aluminum in smooth, ball-milled or script designs. Push-on versions use a washable, replaceable foam screen, and PCV versions use a replaceable valve. Earl's PCV breathers use dual baffles and a 3/8 in. slip-on or -6 AN end.

The RPC clamp-on chrome breather stands 3 in. tall with a 1-3/8 in. I.D. JEGS finned aluminum breathers measure 2-3/8 x 4 in., including a version with a 1/4 in. PCV tube.

Valve Covers: Materials, Height and Baffles

Choose a valve cover by material, height for rocker clearance and internal baffling. Chrome or black stamped steel is the traditional choice. RPC offers steel covers for 1958-86 small-block Chevy, plus tall chrome covers for big-block Ford 429-460.

Cast aluminum covers often use a classic finned design. JEGS fabricated aluminum covers use TIG-welded 0.060 in. 6061-T6 sheet, a billet flange and a 1.25 in. breather hole with a built-in baffle.

Moroso builds fabricated big-block Chevy covers, including one with a -12 AN breather and oil fill. Roller rockers or a high-lift cam usually call for tall covers. JEGS tall chrome small-block Chevy covers sit 1-1/4 in. above stock and clear most performance rockers, but not stud girdles.

Baffled covers keep oil splash away from breather and PCV openings. Proform dress-up kits, like a 1965-up big-block Chevy kit with short black crinkle covers, complete the look. Compare valve cover parts by engine.

Grommets, Hardware and Fitment Checks

Confirm your engine family and breather hole size first. A 1 in. breather won't seal in a 1-1/4 in. opening. Use this checklist:

• Measure the breather hole, since most covers use 1 in. or 1-1/4 in.
• Add grommets when a push-in breather mounts in a steel cover.
• Use rubber oil baffles when a breather mounts in an aluminum cover.
• Order hold-down tabs if small-block Chevy covers need extra flange clamping.
• Add a valve cover bolt kit that matches your finish.

RPC offers grommets for 1-1/4 in. steel cover holes and oil baffles for aluminum covers. Moroso makes small-block Chevy hold-down tabs. Earl's breathers include a grommet but need a hole of at least 1.22 in.

Tighten cover bolts evenly using our small-block Chevy torque specs guide. With the covers off, review how to adjust your valves. Many builders update timing covers at the same time.