What is engine valve lash?
Valve lash is the available clearance (or gap) between the rocker arm and the tip of the valve stem when the lifter for that valve is sitting on the base circle of the cam lobe (when the valve is intended to be fully closed). But on a solid cam and lifter setup, lash is a very big deal because it must be set manually.
What does adjusting valve lash do?
The valve mechanism (push rod, lifter, and rocker arm assembly) is adjusted so that the lash has the proper clearance necessary to regulate the opening and closing of the valve. If the lash clearance is too great, it will affect the engine’s airflow and will eventually lead to valve damage.
What will improper valve lash cause?
Too much or too little valve clearance can result in poor performance or a rough idle because the engine can’t “breathe” normally and operate at peak efficiency. Too much clearance means the valves will likely clatter and, over the long term, cause damage to the valves, camshaft lobes or rocker arms.
What is valve lash measured by?
feeler gauge
Valve lash is measured with a feeler gauge between the tappet adjusting screw and the end of the valve stem. A feeler gauge measurement is either a go or no-go. To adjust valve lash, loosen the locknut (10mm), and turn the tappet adjusting screw until the drag on the feeler gauge is correct.
What is excessive valve lash?
Valve Lash or Valve Clearance is the gap between the Rocker Arms and the valve tappet. This clearance must be tightly controlled. If it is too little, the valves may not seat properly. If you have too much valve lash, you eliminate the more “gentle” sections and are basically “slamming” the valve open and closed.
Why do you need valve lash?
Valve lash is intended to provide the greatest amount of valve opening on the high point of the camshaft lobe and assure that the valve is tightly closed on the low segment of the camshaft lobe. Valve lash adjustment is necessary maintenance for engines without hydraulic valve lifters.
What does valve lash mean and why is it necessary?
Does valve lash increase or decrease when hot?
The lash number that cam manufacturers supply will be the “hot lash,” which is the ideal lash after the engine is at operating temperature. The lash can change several thousandths of an inch between when it is at room temperature and when everything is warmed up properly.
Can valve lash cause misfire?
Bad valve adjustment can totally cause misfire.
Is it better to have tight or loose valves?
Two, is that too loose will hurt nothing, but too tight will result in engine damage, probably a burnt valve. You should be able to hear them, quiet is bad. Slappy valves are happy valves.
How do you calculate valve lash?
To determine the valve lash, subtract the squish from the desired valve opening lift. The cam in the graph is for a flathead, using squish of 0.002″ the valve lash should be 0.0127″ or 0.013″. The exhaust could be set a couple thousandths larger to allow for thermal expansion.
What is the difference between valve lash and valve clearance?
Valve Lash or Valve Clearance is the gap between the Rocker Arms and the valve tappet. This clearance must be tightly controlled. If it is too little, the valves may not seat properly. This lower section is where the cam profile is designed to gently open and close the valve.
What is the purpose of a valve lash?
Valve lash is intended to provide the greatest amount of valve opening on the high point of the camshaft lobe and assure that the valve is tightly closed on the low segment of the camshaft lobe.
What does a lash do in an engine?
Valve lash is the mechanical clearance in the valve train between camshaft and valve in an internal combustion engine.
When to set the Lash on the intake valve?
The best sequence to use when setting valve lash is to go by the firing order. This requires less turning of the crankshaft and will help ensure that valve overlap is not an issue. EO/IC rule (Exhaust Opening and Intake Closing). Set the intake valve lash when the exhaust valve is beginning to open.
Do you need a gauge to set a valve lash?
Setting valve lash on hydraulic lifters does not require a “feeler” gauge. The process is the same for stamped steel rockers (like the ones pictured) or roller tip rocker arms.