FORMULA, SUPERPRO Intake Manifold Bushes with Fitting Position Front and Rear, Front Axle

Intake manifold bushes, including plenum box to manifold bushes, are the small isolating bushes used where parts of the intake system mount to the engine or to each other. They hold components such as the plenum box in position while absorbing vibration and allowing for the expansion and contraction that comes with engine heat. When these bushes harden or crack, the result can be rattles, buzzing from the top of the engine and extra stress on the gaskets and fasteners around them. Fitment is specific to each engine, so use the vehicle search to find intake manifold bushes to suit your vehicle.

What Is an Intake Manifold Bush?

The intake system carries air from the air filter and throttle body into each cylinder. On many engines, it includes a plenum box, a chamber that collects incoming air before it is distributed to the individual runners of the intake manifold. The plenum and manifold are often separate parts, bolted together and mounted to the engine.

Intake manifold bushes sit at some of those mounting points. Rather than bolting the plenum or manifold rigidly, the engine designer uses a bush between the component and its mount. The bush locates the component and clamps it in place, but its flexible material isolates vibration and lets the parts move slightly relative to each other as temperatures change. The exact number and position of bushes varies with the engine design.

Intake Manifold Bushes Versus Gaskets

Bushes and gaskets are easily confused, but they do different jobs. A gasket is a seal. It sits between two mating surfaces, such as the plenum and the manifold, and stops air leaking in or out of the intake. An intake manifold bush is a mounting part. It supports a component and isolates vibration, but on most designs it does not form the airtight seal.

The distinction matters when diagnosing problems. A leaking gasket typically causes an air leak into the intake, while a worn bush mainly causes noise and movement. Worn bushes can, however, let a component move enough to stress the gasket next to it, so the two problems sometimes appear together.

Why Intake Components Are Mounted on Bushes

Engines vibrate constantly, and intake components are often large, light structures that can resonate at certain engine speeds. Mounting them rigidly would transmit that vibration straight through, producing buzzing and rattles, and in some cases fatigue cracks in brackets or plastic components. Bushes absorb much of that vibration before it reaches the component.

Heat is the other reason. The engine block, cylinder head and intake components heat up at different rates and expand by different amounts. A rigid mounting between them would load the fasteners and gaskets every time the engine warms up and cools down. Bushes allow small amounts of relative movement, so the mountings and gaskets are not forced to absorb it all.

Signs Your Intake Manifold Bushes May Be Worn

Common signs include a buzz, rattle or vibration from the top of the engine, often at particular engine speeds where the intake resonates. You may notice the noise is worse at idle or when the engine is cold, before components have expanded to their normal positions.

With the engine off, worn bushes may show as cracked, hardened, flattened or crumbling material around the mounting bolts, or a plenum or manifold that can be moved slightly by hand when it should be firm. Fasteners that repeatedly work loose at the same mounting point can also point to a worn bush, since the clamping force depends on the bush holding its shape.

Other Possible Causes

Engine bay rattles and vibration have many sources. Loose heat shields, intake pipe clamps, air filter boxes and wiring brackets can all produce similar noises. Rough running, a hissing sound or an engine warning light are more likely to indicate an air leak, such as a failed gasket or split hose, than a worn bush. Have the cause confirmed before replacing parts, and have any suspected air leak checked by a technician.

How Engine Bay Heat Affects Intake Bushes

Intake manifold bushes sit on top of the engine, one of the hottest areas of the engine bay. They are exposed to repeated heating and cooling every time the engine runs, along with oil vapour and, on some engines, fuel vapour. Over time, rubber bushes in this environment harden, shrink and crack, losing their ability to isolate vibration and hold their clamping force.

Vehicles that work hard, tow heavy loads or operate in hot climates put their engines through more heat cycles at higher temperatures, which accelerates this ageing. Older engines are especially likely to have hardened intake bushes, even if they have not covered high kilometres.

Rubber or Polyurethane Intake Bushes?

Original intake manifold bushes are usually rubber, which isolates vibration well when new but degrades with heat and oil exposure. Polyurethane bushes are generally more resistant to oils and heat, so they tend to hold their shape for longer in the engine bay.

Polyurethane is also firmer than rubber, so it can transmit slightly more vibration from the engine to the intake components. For most applications, the difference is small, and the improved durability is the main reason to choose it. Check that the replacement bush is designed for the specific mounting point and engine, since the required firmness and shape vary between designs.

Fitting Intake Manifold Bushes: An Overview

Replacing intake bushes usually involves partly or fully removing the plenum or intake component they support. Disconnect the battery before starting, and photograph or label every vacuum hose, wiring connector and breather pipe before removing it, since intake components often carry many small connections that are easy to mix up.

Once the component is removed, the old bushes are pulled or pressed out and the new bushes fitted. Inspect the gaskets while the parts are separated. Many intake gaskets are not designed to be reused, so plan to replace them at the same time. Cover open intake ports with clean tape or cloth while the component is off, to stop debris or fasteners falling into the engine.

Refit the component, tightening fasteners in the sequence and to the torque specification set by the vehicle manufacturer. Uneven or excessive tightening can distort the component or crush the bushes. Reconnect everything, then start the engine and check for smooth running, air leaks and any warning lights. Because of the number of connections involved, this work should be carried out by a qualified technician if you are not confident with intake work.

Checking Intake Bushes During Other Engine Work

Many engine jobs require the plenum or intake components to be removed for access, including some spark plug, injector, coil and sensor replacements. That is a good opportunity to inspect the intake bushes, since the parts are already apart. If the bushes are hard, cracked or flattened, replacing them while the intake is off saves removing it a second time later.

Choosing the Right Intake Manifold Bush Kit

Intake manifold bushes are specific to the engine. The number of bushes, their size, shape and position all vary between engines, even within the same vehicle model. A kit designed for one engine's plenum will not suit another. Confirm your vehicle's make, model, year and engine before ordering, and check that the kit covers all of the mounting points on your intake that use bushes.

Shop Intake Manifold Bushes with Formula 4x4

Intake manifold bushes sit in the Formula 4x4 engine parts range.

Start by confirming that the noise or movement comes from worn intake bushes rather than an air leak or a loose component elsewhere. Search by your vehicle to find intake manifold bushes to suit it, and plan to replace any intake gaskets at the same time. If you are unsure which part your vehicle needs, contact the Formula 4x4 team.