Racer Chris Hargett and engine...
Racer Chris Hargett and engine builder Jim Cook lash the valves on Hargett's Dirt Late Model. This isn't necessarily a two-person job, but having someone to turn the engine over with a bump starter while you check valve lash can speed things up considerably.
The single most expensive component of any race car is by far the engine. Of course, most racers don't seem to mind paying for power; it's paying for repairs that they hate. Thankfully, many problems that can cause an engine to detonate on the racetrack can be avoided with a quick checkup of your engine's health after every two or three races.
By sticking to a scheduled monitoring program of your engine's valvetrain, you can potentially save yourself a lot of money by catching small problems before they become big ones. After all, it isn't expensive to replace a valve or lifter-or even a complete set of springs-but a broken valve flopping around inside the combustion chamber or a dead lifter sending tiny bits of roller-bearing shrapnel throughout the engine amounts to a hefty repair bill and perhaps the end of your season. These three simple checks can be done in less than an hour and will give you an excellent indication of the health of your valvetrain.
If the lash ever moves more...
If the lash ever moves more than a couple thousandths of an inch in either direction after a weekend of racing, you should check further for potential problems.
Check The Valve Lash
Valve lash is the available gap between the rocker arm and the tip of the valve stem when the cam lobe for that valve is on its base circle (fully closed). Lash is only an issue with solid lifters-either flat-tappet or roller-and should be checked after every race, or at least every other race. Valve lash will change even if your rocker adjusters are locked down tightly, so they will need to be periodically adjusted to keep the lash within proper specs.
The proper amount of lash will be provided by your engine builder or camshaft manufacturer, but it is usually between 0.010 and 0.024 for race engines. With normal use, you should notice your valve lash slowly decrease, especially with a new engine. This is because of wear between the valve and the valve seat, which allows the valve to sit slightly deeper in the head. This should be considered normal wear and isn't a sign of concern unless you have one valve move two thousandths of an inch or more after a race.
What is a cause for concern is the valve lash opening up. The most common reason for this is a failure of the needle bearings in a roller lifter or a wiped cam lobe. "Wiping" a cam is knocking the crown off of the nose of the lobe. At this point the cam-and probably the lifters-must be replaced. A broken axle or failed needle bearings in a roller lifter isn't as big of a deal, but the lifter should still be replaced immediately to avoid the possibility of further engine damage.
Cook checks the on-head spring...
Cook checks the on-head spring pressures and compares them to previous readings in his log book to see if any are failing.
Check The Valvesprings
Many racers fear a broken valvespring because it usually means a valve is allowed to bang into a piston, and there is no telling how much damage will be done after that. Thankfully, most valvesprings give plenty of warning before they fail, but you have to know what to look for.
The best method is to begin tracking valvespring pressures on your engine when the engine is brand new. You will need an on-head spring checker, which is available for around $75. Begin by checking and recording the rated pressures on all 16 springs and logging them in your notebook. After that, check at least four springs randomly after every couple of races and log those pressures. (You might as well do this whenever you lash the valves and already have the valve covers off.)
Typically, a new set of springs will experience a drop in pressure after the first few engine runs and then level off. This is to be expected. But when you notice a spring losing strength again after that, it means that it is in the process of failing and should be pulled from your engine immediately. If you notice more than one spring failing at the same time, you might as well change the complete set.
Use a small flashlight to...
Use a small flashlight to visually inspect the valve stem seals. If they are chewed up, it can be because an inner spring has broken.
Get Out The Flashlight
The only tools you will need for your final check is a small flashlight and a sharp eye. If you are running nested valvesprings, it can be difficult to visually inspect the inner spring. Engine builder Jim Cook recommends inspecting the valve stem seals instead. If you have a broken inner spring it will usually chew up the seal. If you notice stem seal damage, it means you will need to pull that spring and take a more complete look at the assembly.