One of the things that many home mechanics run into that can be a little confusing the first time you do it is setting Valve Lash on Solid or Hydraulic Lifter Engines.
There are a variety of reasons that you might want to check or set your Valve Lash and that can be when you are rebuilding or repairing your engine. Maybe you are changing your camshaft or maybe you just want to do a full tuneup of an older engine and make sure everything is working and set correctly.
What is Valve Lash?
Valve Lash is when you adjust the center rocker nut on your heads that acts as an activator or lever that opens your valves when your push rod is pushed up by your lifter when your camshaft turns.
Basically if you don’t understand that last paragraph you probably shouldn’t be adjusting your valve lash but I will explain it in a little more detail in case someone is just researching what they need to learn.
When your engine runs a number of things happen but lets just concern ourselves with the parts we will be working on.
In the engine cylinder you have a piston that goes up and down four times to complete the stroke cycle. The stroke cycle consists of: Piston Down for intake to get fuel into the cylinder, Piston up to compress the mixture, Piston down again after the spark plug ignites the fuel, finally piston back up to expel the spent gas vapor.
When the Piston is at the top of the stroke the valves can be open or closed depending on if they are expelling exhaust, getting ready to allow new gas in, or closed for combustion.
On your head you have 2 valves per cylinder. One delivers fuel and the other expels exhaust.
The Valves are normally held in the closed position by strong springs that the valve stems pass through You will see the springs when you open your valve cover. To open the valve a rocker arm presses down on the top of the spring and valve stem to push the valve open.
The rocker arm is pushed by a push rod that is resting on a lifter that is resting on your camshaft.
The camshaft has a gear on the front of it which is connected by a chain loop to a gear on the crankshaft. This allows the valves to open and close in unison with the pistons and the position of the piston in the cylinder.
Ok so hopefully you got something from that.
If we go back to the part where the Valves are normally closed and held closed by large springs on top of the head and the rocker arm pushes on that valve stem to open it then this is where we begin the valve lash adjustment.
Knowing Your Lifter Type
Most vehicles will have a Hydraulic lifter which kinda acts like a shock absorber. Very few vehicles have solid lifters which are basically little solid steel barrels with no give. You will find solid lifters on race engines and on very old vehicles that predate hydraulic lifters.
To adjust a Hydraulic Lifter you want to put some compression load on the lifter.
For Solid lifters you want to use a Feeler Gauge and set a small gap so that there is no load on the lifter, push rods or valves.
Normally you won’t set the valve lash on hydraulic lifters for the life of the engine unless you are changing or working on the engine in a way that could change this load. That might be when you are replacing a head or having it milled because of a head gasket or something of the type.
For solid lifters it will depend on your use of the engine on how often you need to set the valve lash. If you are racing the engine then it might be after every race or after every rebuild or maybe once every couple weeks or months if you are just having fun and not doing it professionally. You will have to check with the manufacturer on how your solid lifter adjustment schedule should be completed.
This is why most engines have hydraulic lifters so they do not require major intervention every few months or so.
Setting The Valve Lash
The valve lash is the distance or pressure placed on the top of the valve stem by the rocker.
VERY IMPORTANT: Valve Lash must only be set when the camshaft is rotated so the lifter is on the round or back side of the cam and not on the top of the camshaft lobe. To do this you know that when the intake valve is at its maximum lift and the push rod is actuating the rocker arm that the Exhaust Valve is on the back side of the camshaft and not on the Lobe of the Camshaft.
It takes quite a long time to adjust the valve lash on all of your valve because you will need to continuously turn the engine with a wrench on your crank shaft bolt until the intake is open and then adjust the exhaust valve and then turn again until the exhaust valve is open and adjust the intake valve for each cylinder. It is important to take your time and do this right. Some people suggest shortcuts like when the number 1 intake valve is open you can adjust other valves too but I strongly suggest you don’t do this because you could lose track of what you are doing. Just do each piston and its valves and move on to the next cylinder and its valves and when you are done you will be sure you got it right. If not go back and test a few (especially on solid lifters.. double check).
Tightening The Rocker Nut
Now for Hydraulic Lifters the normal process is find the back side of the camshaft so the valve is not being compressed and then tighten down the rocker nut until the rocker is not wobbling and is tight and then give the nut a 180 degree or half turn.
On a Solid Lifter you find the back side of the camshaft and tighten down the rocker nut until it is just touching. Then you back the nut off so there is room between the top of the valve stem and the rocker. Then you use a feeler gauge like you use to set points or spark plugs and you set it at about 20 to 30 thousandths of an inch. You need to check your manufacturer for the correct feeler gauge to use.
So, on Solid Lifters you are setting a Gap and on Hydraulic Lifters you are tightening the rocker arm down just enough that the rocker arm touches without pressure and then giving it another half turn.
This process is time consuming and if done wrong can cause a variety of problems for your engine. Everything from poor performance to physical damage. Reading Documentation from your manufacture is important when setting your valve lash just like any other setting on your engine. If you have doubts about anything the manufacture should have a way to contact their help desk or maybe even online information and videos for your specific product.
The skill level of performing this task is pretty low but it can take some time and is repetitive.
I also suggest that you remove your spark plugs to reduce the resistance you will have when turning the crank.