Warning Signs that Might Save Your Engine from Destruction
Forensics has become a 21st-Century buzzword. There are even forensic accountants–they work at uncovering dubious business practices that perpetrators prefer to remain hidden. That same forensic specialist tag could be placed on a good engine builder who closely monitors his engine for clues that it may not be happy.
High RPM, high-output race and street engines are fickle mistresses. They demand constant attention because the valvetrain parts are at or always near their limit – especially when asked to spin at stratospheric engine speeds. Perhaps among the most abused are those street engines that also spend time at the drag strip. Drag Week engines could be among the most thoroughly mistreated since they must rumble down the road for 1,000 miles and still be capable of daily big-power and RPM numbers.
All of this can extract a toll on the valvetrain. Valvesprings, rocker arms, pushrods, lifters, and even retainers and locks are among the most highly stressed components in any internal combustion engine. If you pay attention to your engine’s subtle cues, you can prevent sometimes-catastrophic failures before they happen. It takes a keen eye and attention to detail but we can help by offering important places to look for signs of distress.
Much of this information comes courtesy of Ben Strader at EFI University and Billy Godbold of Comp Cams. Strader is currently tweaking this particularly healthy 358ci LS engine covered previously here on EngineLabs. It features a 4.185-inch bore, 3.25-inch stroke, Dart LS Next block and RHS LS7 heads, and an aggressive mechanical roller camshaft with 280/294 at 0.050 duration and over 0.800-inch lift. The engine has made 867 hp at 8,600 rpm and has repeatedly spun past 9,000 rpm.
As you can imagine with a combination like this, it’s very sensitive to valvetrain stress, so Strader offered some insightful information as to what and where to look for signs of impending doom.
The Lash Effect
Assuming we will be dealing here with mechanical roller engines, checking lash should be a clockwork stop on your maintenance program. Lash is the first and often best telltale sign that something’s amiss. Most often, a change of 0.002-0.003-inch on one or two valves might be enough to signal a problem.
Generally, wear will increase lash, but we’ve seen instances where the hot clearance actually tightens. This can be caused by valve seat regression where the seat has been pounded into the head slightly, reducing the lash. We’ve also experienced an issue with a brand new head where several intake rockers lost nearly all their lash. This was created by a bad set of valves that began stretching. Another couple of pulls on the dyno would have seen these valves fail spectacularly. Attention to detail was rewarded by preventing an otherwise ugly valvetrain failure.
We’ve included a dyno example from our friends at Westech Performance Group of a loss of valve control as revealed by the power curve. Note that above 6,400 rpm, power experienced a dramatic dip. This is a clear indication of loss of valvetrain control. But you don’t need an engine dyno figure this out. Any time the engine abruptly quits pulling, this can be an indication of loss of valvetrain control. This can happen at any RPM – not just at 7,500 rpm or beyond. We’ve seen hydraulic-cammed big-block Chevys experience this loss of control at 5,400 rpm.
The more subtle indicators will require closer inspection and disassembly. Obvious issues like bent pushrods are easy. The clues that can save an engine will be harder to spot. For example, when disassembling the valvesprings, be careful to note how the locks and retainers come apart. If the locks fall out easily when spring pressure is removed that is a good sign. If you have to pry the locks apart from the valve, that’s a hint they have been pounded by the retainer. This occurs for many reasons but it could be caused by spring surge issues.
Anytime an engine runs, waves that traverse the spring will impart load both when the valve is open and on the seat. If the retainer is unloaded because of loss of control, when pressure is regained, this will tend to impact the locks, causing them to stick on the valve. Other evidence of damage will be shiny spots between the locks and retainers, and you could also see wear marks on the spring side of the retainer and on the spring seat. Any movement here is an indication of loss of control.
A quick way to determine if the springs have suffered damage is to record the seat and open pressures on each spring when new and then after a dyno session or two it’s a good idea to check the loads again. With the engine in the car, there are several lever tools that do a decent job of compressing the spring to check the installed load. When the engine is apart, a bench spring checker can easily perform this task. Most machine shops have one of these tools but they are not all that expensive if you plan on performing race engine maintenance.
While a weak pushrod can cause loss of control, it may be masked by symptoms that do not immediately point to the pushrod.
The best place to start your investigation would be to call the spring manufacturer and discuss your valvetrain combination.
This actually illustrates an important point that the valvetrain should be evaluated as a system even though this story breaks this discussion down to separate components. While a weak pushrod can cause loss of control, it may be masked by symptoms that do not immediately point to the pushrod. Increasing spring pressure to overcome this problem could only aggravate it. This is where consulting with your cam or valvetrain supplier can point you toward the solution. Many companies like Comp Cams or Trend Pushrods have their own in-house Spintron test machines that allow the manufacturer to perform an immense amount of testing to determine proven valvetrain combinations.
Valvetrain weight also plays a crucial part in this scenario. Reducing weight is especially rewarding on the valve side of the rocker arm. Valve acceleration rates created by the cam lobe are multiplied by the rocker arm ratio, so reducing the mass of the valve, spring, and/or retainer is a great way to improve stability. The EFIU’s LSNext engine’s stratospheric speeds were made more manageable by reducing the retainer weight of 21 grams (with tool steel retainers) down to 12 grams. By switching to a set of titanium retainers, a measurable improvement in durability was observed by eliminating movement between the retainer and the spring. Keep in mind that while 9 grams might not seem like much, that’s a retainer weight trim of nearly 43 percent. For a high-RPM engine like this one, the savings is significant.
Moves like this can also be accomplished even for milder street engines. With large diameter valvesprings, steel retainers can be very heavy. Tool steel retainers are nearly as light as titanium yet are roughly half the cost. A set of Comp Cams steel retainers for a 1.450-inch dual spring can cost only $51 while the titanium version is nearly $300.
One of the latest trends toward reducing valvetrain distress is the conical valvespring design. Many modern production engines employ beehive springs that reduce the size of the retainer, which reduces mass. The conical design expands on this by gradually tapering the spring diameter from the base to the top. This reduces the size of the retainer, but more importantly, the taper drastically improves the spring’s response to high RPM use. The current version of this is Comp Cams’ PN 7245 dual conical spring that uses a conical inner spring that, unlike all dual spring combinations, is designed to avoid contact with the outer spring. This reduces stress on both springs and also drastically reduces heat. There is a significant cost associated with this technology, but the advantages can be well worth the price of admission. Strader’s LSNext engine employs a set of the 7245 springs and has had obvious success with them.
There are many more clues to valvetrain instability but the few we’ve listed here should help dial in your valvetrain in the search for more control. This is one place when being a control freak is actually a good thing.