Drag Race 101: Valve Springs Primer
Valve springs are probably the most overlooked part of the valve train when building an engine, whether it’s a daily driver econo-car or a full-blown race car. This is a shame, especially when you take into consideration how many times engine failures during a race or pass are traced back to faulty springs. If it can happen to engines that are meticulously engineered to the finest detail, it can very easily happen to yours.
We’re going to discuss valve springs in some detail. We’ll first tell you where they’re located and what they do. I will next go into some detail on how valve springs can fail. There are a couple different designs that are used for valve springs, so next I’ll jump in and give those a mention. After that I’ll mention some of the most popular brands that are available, and finally, I’ll give two short How-Tos on how to remove and replace (R&R) valve springs, both with the engine together, and disassembled.
What Are Valve Springs and What Do They Do?
As their name implies, valve springs are springs that are used in conjunction with the engine’s valves, both intake and exhaust. As the camshaft turns, causing the valves to open and close, a force outside the pressures generated in the combustion chambers is needed to cause the valves to close quickly and completely when the cam lobe rotates to the proper alignment. We use valve springs to perform this function.
The valve spring is located in the top of the engine cylinder head and there is usually at least one valve for exhaust and one for intake per cylinder, although most high performance engines have multiple intake and exhaust valves per cylinder. The valve springs surround the valves and can be found either between the rocker arm and the head in cam-in-block engine designs, or between the camshaft and the block in overhead cam designs. The valve is inserted in the valve guide from the underside, the spring is installed and compressed, a set of locking clips are installed to retain the spring, and the spring is decompressed.
How Valve Springs Can Fail
A valve spring is said to have failed when it is no longer able to properly seal the valve against the seat every revolution of the camshaft. This can happen in a number of different ways, but there are two main ways this happens:
- The spring cracks or breaks
- The spring weakens, losing the strength of its “springiness”
A valve spring can fail for a few different reasons, such as defective production techniques or materials, or incorrect application, or usage. The why behind defective materials or manufacturing processes are obvious; poor materials won’t stand up to repeated abuse and a manufacturing process with defects will produce defective products.
Incorrect application is a different beast narrowed down to the simple statement: “It don’t fit right!” This can mean several things:
- The spring diameter is too large or small
- The spring length is too long or too short
- The spring tension is incorrect
- The wring design was used
Get the Right Spring for the Application
How different can different valve spring designs be? They’re just fancy springs, right? Well, in a way, yeah, they are just fancy springs. But they perform a very important function and therefore quite a bit of thought and energy is put into their design and manufacture. If you’re building an engine from scratch and building the heads, or rebuilding the heads, you also need to take spring design into consideration.
There are two basic designs of valve springs: Single spring and interference fit, or dual springs. Singe springs are just that-a single spring used to control the closing of the valve. Dual, or interference fit, springs have a smaller spring inside the larger outer spring to increase the spring tension applied to the valve to close it.
Once you’ve figured out whether you need interference fit or single springs, you need to determine the other variables. You need to make sure the spring fits in the pocket machined into the head. That means correct width. You also need to make sure that it isn’t too long to compress and lock properly, while still making sure it isn’t too short to lock the keepers and retainers in place when closed. Finally, you have to make sure that the spring tension itself isn’t too great or it will cause rapid and premature aging and wear of the camshaft and rockers.
Some Popular Makers of Valve Springs
There are quite a few more makers of valve springs now than there were when I was building performance engines on a regular basis. Back then, we called our jobber and ordered matched sets from manufacturers such as CompCams and Edelbrock. Unfortunately, I’ve discovered in my travels that parts stores like that are becoming more and more rare over time and rodders and racers will need to consult catalogs from distributors such as Jegs and Summit.
Whether back then or today, if I’m rebuilding a head or a set of heads for daily drivers, I’ll review the manufacturer’s own specs for the valves and then order a set of either Manley, Crower, or Brodix. These brands have been around for longer than I’ve been a part of the automotive scene (Reagan had only been a poor actor and so-so governor when I started). Of course, the automakers, through their suppliers, are all suppliers of quality valve springs. There are now many more.
Some of the newer manufacturers of valve springs include Air Flow Research (AFR), PAC, ProMaxx, and Scorpion. When either rebuilding a head, or building a new head from scratch, you need to make sure you order the correct parts, including valve springs. Check the manufacturer’s specs for the spring online or email them for the specs (height, diameter, thickness, single/dual, etc.) so that you can be assured of getting the right ones.
How to Install New Valve Springs
Valve springs can be installed either with the head installed, or off the block. With the right tools, both methods work equally well and neither takes longer than the other. The steps involved in the R&R of the valve springs are similar whether the head is on or off. A quick run-down of those steps follows.
The steps for performing an R&R of the valve springs with the head on the block are as follows:
- Apply pressure to the combustion chamber side of the valve in order to keep it closed during the process of removing and installing the springs. This can be done with compressed air, or, if you’re brave, engine compression. Drop the valve and you will have to pull the head.
- Apply the valve spring compressor tool to the lowest and highest coils of the spring possible and compress the spring until it is loose on the valve.
- Remove the retainer and keepers and remove the spring.
- Decompress the old spring and remove it from the tool.
- Install the compressor on the new spring and compress the spring until it fits over the valve properly so the retainer and keepers can be replaced.
- Replace the retainer and keepers and slowly decompress the valve spring.
- Repeat this process on the rest of the valve springs.
The process for the R&R of valve springs when the head is off is a little different and can use a different design of valve compressor tool (See image above) that applies pressure to the underside of the valve as the spring is compressed. Here’s how it’s done:
The second type of spring compressor shown in use.
- Slip the bottom of the compressor tool over the bottom of the valve.
- Slide the notched opening around the top of the valve and spring.
- Slowly compress the spring until enough tension is removed to remove the keeper and retainers.
- Remove the keeper and retainers.
- Decompress the valve spring, remove the tool, and then the spring.
- Hold the valve in place, place the valve spring into place and properly align the compressor tool.
- Compress the valve spring sufficiently to install the retainer and keepers.
- Repeat the process as necessary.
The first type of valve spring compressor tool can be used either head-on or head-off and is actually a bit easier (to me) than the other type of compressor.
So there you have your primer on valve springs. Got questions? Have something to add? Let us know below in the comments!
So You Want to Be A Drag Racer: Buying, Building, Wrenching and Racing
The allure of the drag strip is easy to understand – a place where it takes less than 10 seconds to make a stand, prove your skill, speed, and nerve. But the road to the races can be intimidating. The Burnout wants to make that road a lot smoother for aspiring racers, whether it’s through building a new car, modding a used one, or taking that ride all the way up to the burnout box and beyond. This series is a work in progress, an ever expanding comprehensive guide to all the things that take drag racing from concept to reality.
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