How Crankshafts and Camshafts Work

How Crankshafts and Camshafts Work

Last Updated May 7, 2019 | Meghan Drummond
Contents

The relationship between camshafts and crankshafts affects every area of engine performance. Though the function of a camshaft is very different from the function of a crankshaft, it’s only by moving together and maintaining synchronization that either is able to work.

It’s good to understand how these two important engine components work together, what the signs are that they’re no longer functioning, and what options are available for cam and crankshafts if you’re in need of a replacement or looking for an improvement.

Your Engine Block

Depending on your vehicle, you may have either an overhead valve or an overhead cam style engine, regardless, the relationship between the camshaft and the crankshaft and what aspects of the engine each control will end up being roughly the same, only the locations of the camshaft will change.

In an overhead valve engine, a single cam is situated in between the engine’s cylinders, and from there operates the intake and exhaust valves via a set of pushrods, which is why this engine style is also called a pushrod engine.

In an overhead cam, or modular, style engine, multiple camshafts will sit on top of the cylinder heads. Like in an overhead valve engine, the valves are operated via the camshafts’ rotation. Depending on the setup of the engine, it may be a single cam per bank of cylinders or multiple cams.

An engine with two cams over each bank of cylinders
A Dual Overhead Cam Engine

Crankshaft

Below all of the cylinders, at the base of the engine, a crankshaft is what moves the pistons of an engine. Connecting rods tether the pistons to the crankshaft, and as the crankshaft turns the pistons move up and down.

When the pistons move up, they compress the air and fuel mixture in the cylinder, creating a reciprocating motion that propels the pistons down, pulling in more air and fuel. The end result is a four-stroke cycle, the fundamental basis of most internal combustion engines. But in order for this to function the way it needs to, valves need to operate in perfect time to both admit additional oxygen and also to expel exhaust as necessary.

Camshafts

Camshafts look like a metal rod covered in lobes of various sizes. As these lobes turn, they operate the intake and exhaust valves, either through tappets or rocker arms in an OHC engine or through pushrods in an OHV engine.

It’s not unusual for engines to have as many as four camshafts. This is because as engines have improved, one of the ways that auto manufacturers have discovered to increase their fuel economy and performance is to allow cams to vary their timing as needed, which requires multiple camshafts. By using quad cam lineup in a V-shaped cylinder engine, there can be a single cam for the intake and exhaust on both banks of cylinders. This is referred to as variable cam timing, and though every brand has their own name for it and there are slight variations, it boils down to allowing cams to vary the speed of their intake and exhaust valves.

Lift is an important attribute of a camshaft, but it can be misleading. Lift is good, since a greater lift allows an engine to intake and expel air more freely, and improving airflow is one of the easiest ways to improve the overall performance of an engine.

When a camshaft has excessive lift though, it can create a problem called valve float. Valve float can lead to an engine overrevving. Ideally, you want enough lift that the valve is able to allow plenty of airflow, but so that it also continues to follow the camshaft closely.

Connecting Camshafts and Crankshafts

In order for the intake and exhaust valves to line up precisely with the up and down cycles of the piston, the camshaft and crankshaft must work together with precise timing. In order to do that, a timing belt, timing chain, or other synchronizing device connects the two shafts.

In overhead valve engines, it’s also possible for a direct gear drive to connect the camshaft and crankshaft. This is one of the sturdiest connecting methods, but because of how close the cam and crankshaft have to be in order for it to be effective, it isn’t common, even in pushrod engines which will typically still use a timing chain, though a much shorter one than is necessary with an overhead cam design engine.

Timing belts are typically a toothed length of rubber composite. This is one of the most cost-effective options, though it’s not the most durable. Another benefit of rubber timing belts though is that they tend to be the lightest of all options.

Timing chains are roller chains, exactly like what you might find on a bicycle. Just like a bicycle chain, it’s important for timing chains to maintain lubrication, otherwise, they can cause damage and will operate much more harshly than they should. Eventually, timing chains will stretch and wear out, just like your bike chain.

Regardless of what type of timing device you have, eventually you will need a replacement.

Diagram of a timing belt connecting a cam and crankshaft
Camshaft and Crankshaft

Signs You Need a New Timing Device

Whether your engine is operated by a belt, a chain, or even a direct gear, it’s important to recognize the signs that something may not be operating correctly. If your car develops a rough idle, backfires frequently, or seems to be working incredibly hard for very little motion, then it’s possible that your timing mechanism is no longer functioning as intended and the timing of your cam and crankshafts are no longer matching up as intended. If you ignore this, eventually your car just won’t start at all.

Most manufacturers recommend replacing your timing belt or chain every 30,000 to 50,000 miles, but things like excess dirt or grease can cause premature belt failure, so it’s important to be alert and paying attention to your engine’s performance.

Camshaft Replacements and Improvements

The lobes on a camshaft can come in a variety of shapes, from round, to elliptical, to heart-shaped, or snail-shaped. Elliptical cam lobes move in an egg shape, creating higher lift. When you’re reading the specifications of an aftermarket camshaft, typically you’ll find information on how much additional lift you should see over the stock camshaft. Though this distance isn’t typically much (usually measured in millimeters) in terms of percentage increase it provides substantive gains.

A diagram showing camshaft lobe shapes

Because camshafts affect the aspiration of your engine, they’ll also affect engine sound in addition to performance.

There are several other important considerations when thinking about getting an aftermarket camshaft. Due to emissions regulations, not all camshafts are 50-state legal. Most importantly, you want to be sure that any camshaft replacement your purchase matches the general build of your engine and direction you plan to take your build in. It’s pretty common for people to place too much importance on a camshaft while not upgrading other engine components.

Having one high-performance engine piece without other pieces that are capable of handling the additional output is more like to hurt than help your experience driving your vehicle. That said, upgrading cams is a serious performance boost for those who are looking for real gains even if they aren’t as easy to show off as a new spoiler, wing, or splitter.

Whether you need a new timing belt, timing chain, or are looking to improve your overall performance with an aftermarket camshaft, you can find what you need at CJ’s.

Image Credit: Midwestern Engine and Machine, Quora, Explain That Stuff, Tomorrow’s Tech

Camshafts and Crankshafts

Camshafts and crankshafts are two important components of an internal combustion engine that require a connection in order to work. Though they control different parts of the combustion process, each relies on the other in order to keep turning.