Wander into the pits at any big drag race event and you’ll find racers draped over an engine with the valve covers off inspecting the components, checking valve spring pressure, and setting valve lash. Most racers perform this inspection dance after every round of qualifying or competition.
Take a hint from those racers and keep an eye on your engine’s valvetrain happy. Over the years valvetrain components have become more sophisticated (and costly). Valve spring pressures have increased dramatically. Shaft rocker systems are the norm rather than the exception.
Valve Spring Seat Pressure
When you look at a valve spring spec sheet, you’ll see two types of pressure listed. Seat pressure is the amount of tension or pressure a valve spring exerts when the valve is closed, or “on the seat.” If there were no pressure, then the valve locks (keepers) will fall out and the valve will drop.
Open pressure is the amount of pressure a valve spring exerts when the rocker arm is at maximum cam lift. And with today’s springs, that’s a big number.
Checking open pressure is not very easy or practical with the valvetrain installed on the engine. That’s why seat pressure is the chosen measurement. When you check spring seat pressure and find it has deviated from pressure rating when the engine was built, you have a problem. Usually this means the spring is weak and the valves will float early or the spring is on its way to breaking (or already has).
Most valve spring manufacturers will provide you with the seat pressure number for your combination at a specific spring installed height. If the seat pressure is too high, all sorts of issues can result. The most common is catastrophic valvetrain failure and ultimately engine failure.
Here’s a story that illustrates why valve seat pressure is so important:
When I had a speed shop, a customer came in and purchased a lumpy solid flat tappet camshaft for his brand new L72 427 big Chevy crate engine. Instead of using the recommended valve springs, he insisted on installing the biggest, baddest roller cam-applicable springs we had in stock. I protested, but he simply told me if I didn’t sell him the springs, he’d just go up the street and buy them elsewhere. So, I gave in and sold him the springs.
The very next weekend, the customer was at the local track with his big block Camaro. He made a massive burnout. The car picked up the wheels at the launch and suffered an insanely cataclysmic engine failure by the 60-foot mark. I went over to his house a few weeks later to survey the carnage. Honestly, it was spectacular. The camshaft had broken into pieces and annihilated pretty much everything else. Aside from the water pump and a lightly damaged intake manifold, there was absolutely nothing left to salvage. Long story short, don’t be this guy.
Checking Valve Spring Seat Pressure
A great tool for checking seat pressure is the LSM Valve Spring Seat Pressure Tester. Available in several pressure ratings, the tool can be used with shaft mount and stud-mount rocker systems mounted on the engine. They come with a liquid filled gauge and an adjustable shim pack. That allows you to fine-tune adjustments to within 0.050-inch of rocker arm pivot length.
The LSM seat pressure tester shown in the photos has a multiple handle option. Use the short handle when checking valve springs that have other adjacent components in the way; a good example is a brake booster or master cylinder. When you finish checking those springs, you can screw on the handle extension and finish the rest of the springs. A starter bump switch is your friend here.
There are several other adjustments available. For example, the gauge can be swiveled to clear components. It’s also possible to adjust the tool centerline-to-rocker roller tip centerline distance by juggling the position of the tool load rollers in the frame and using the shim pack. See the photos for more details.
To check seat pressure, install the LSM tester on a rocker arm and gently rock it side to side to square the roller on the rocker body. Pull the tester toward you and slide its hook onto the pushrod. This centers the load roller and brings the pressure up on the gauge. You’ll only need finger-tip pressure to pull the tool.
To check seat pressure, pull the tool’s handle toward you until you feel the valve come off the seat. Again, gently rock the pressure tester side to side a few degrees in order to double check that the tool is square against the rocker body. Now take the pressure reading on the gauge. What you’re looking for is consistent, repeatable results.
Setting Valve Lash
Another really big issue with modern valvetrains is over-tightening the rocker arm jam nuts. This goes double for shaft-mounted aluminum rocker arms. Go too far and you can crack a jam nut or cause it to seize in the rocker. Personal experience has taught me that often means buying a new rocker.
Under-tightening can result in a rocker adjuster nut coming loose. That isn’t exactly a wonderful scenario either. The solution is to properly torque the adjuster nut. Unfortunately, you can’t do that with a regular torque wrench because there’s no way to access the hex head adjuster.
The solution is the LSM Valve Lash Adjusting Torque Wrench. The tool has a hollow 3/8-inch drive that accepts a socket of the appropriate size for the adjuster nut. The included T-handle goes right through the socket; a bushing keeps the T-handle square inside the socket. Place the hex key into the adjuster screw and the socket over the rocker arm nut.
To use the tool, loosen the adjusting nut and tighten or loosen the adjusting screw as needed to reach your valve lash specification. Double-check the lash using a regular feeler gauge. With lash confirmed, retighten the nut until the torque wrench handle frees up.
While the LSM wrench was originally designed for shaft-mount aluminum rockers, it can be used on regular stud-mount roller rockers. According to LSM Racing Products:
“On stud-mount rockers you torque the set screw in the poly lock, not the adjuster like with shaft-mount rockers. To use the TQ-100 on stud-mount rockers you attach a 3/8-inch drive, 7/32-inch hex/Allen bit socket and use a box wrench. No T-handle hex key is involved. Loosen the set screw in the poly lock with the TQ-100 and the hex/Allen bit socket. Make your adjustment with a box wrench and then torque down the set screw with the TQ-100.”
As you can see, these LSM valvetrain tools are great additions to your toolbox. They’re certainly not bargain bin priced tools, but they’re very high quality and in many aspects, extremely unique. Let’s take a closer look at them.









(Image/Wayne Scraba)

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