Setting Valve Lash
(The easy way)
I get many inquiries about setting lash and many times it seems this method confuses people needlessly. There are other methods, but this one has advantages:
1. 1. No need to memorize firing orders ( you don’t even need to know what engine you are working on)
2. 2. On most engines, doing one side at a time, you need to turn the engine very little to get to the next valve needing set.
3. 3. Quicker than most methods.
Most other methods require you know the firing order, carry a little card to tell you “ find your glasses so you can read this card, put the exhaust valve on #1 on base, wiggle your nose, set #8 intake and # 2 Exhaust, turn the engine 37 degrees”, etc. Most require having both covers off and bouncing from side to side on the car, This is a waste of time , can allow the engine to cool off too much if you are not experienced, allows more chance of dirt in the open engine etc…
I suggest reading this in its entirety before starting.
REFER TO THE BELOW DIAGRAM WHILE READING THIS
The key to understanding this method and remembering it properly is understanding the above diagram. In any 4 cycle engine, the order of events is intake, compression, power, exhaust. This repeats over, so by writing out 2 cycles it becomes obvious that the exhaust valve will open before the intake. Also note that before the exhaust closes completely, the intake begins to open, creating a period of time in which both valves are open. Following that period, the intake opens and closes and then there is a period where both valves are closed. The bigger the cam, the shorter the last period becomes.
On to the method * the following is for solid lifter (flat or roller) cams:
1. Take the valve cover off the driver side after warming the engine up. (Most lash settings are hot measurements-if you adjust them too cold the lash will be too loose)
2. Roll the engine over until #1 Exhaust just starts to open- this insures you are on the front side of the lobe, NOT the overlap side, thereby insuring the intake is not open. At this point, you will adjust the intake lash on that cylinder.
3. Once you have adjusted the intake lash turn the engine until the exhaust opens all the way and closes, and the intake opens and is very nearly closed again. This insures you are on the back side of the intake lobe and the exhaust must be fully closed. The reason for stopping just shy of the intake fully closing is to make sure you don’t go too far and pass thru the both valves closed area and start back opening the exhaust. Adjust the Exhaust valve now.
4. Proceed to the next cylinder and repeat the process until that side is done. On many engines, Mopar and Chevy for example, you will notice you have to do very little turning with the exception of one cylinder on the passenger side- this saves much time and effort.
5. Once the driver’s side is done, proceed to the passenger side while your help reinstalls the driver’s side valve cover they cleaned while you were adjusting the valves…..If you are new at this you will likely need to restart and warm the engine between the driver and pass side adjustments- this is another reason to use this method rather than having both covers off.
To recap, on each cylinder, roll the engine until the exhaust just starts to open and adjust that cylinders intake. Then roll thru the exhaust completely opening and closing, the intake opening and just before it is closed, adjust the exhaust on that cylinder. Repeat until all cylinders are done.
Now for some technique….
One of the most common mistakes I see is holding the gauge wrong. You need to hold it on the same angle as the valve tip as below-
Do NOT hold it with down or up pressure as below- this gives an inaccurate adjustment due to the gauge occupying more space than it should or dragging on the retainer/rocker-
When the rocker is adjusted properly, there will be a fair amount of drag when you pull it out- a gauge .001 bigger should not fit –you should barely be able to insert the gauge back in once you remove it.
Be aware of the side pressure on the rockers-when one is open it can sometimes “drag” the other one open-this is one of the main reasons for adjusting when the rockers are nearly closed- if you are not sure, wiggle the one you are adjusting a little to make sure it is free to move . If it is tight, bump the engine just a bit (15-20 degrees) to free it up.
If you are lashing a new engine prior to fire up, or setting the valves cold for some other reason, be aware that they need to be TIGHTER than the hot lash except on all iron engines. I recommend setting cold only when you have to- the only proper way to get the exact adjustment is hot as specified. The below is recommendations which are relatively common- a few thousandths loose probably won’t hurt just to get the engine warm as long as you don’t take it to 10,000rpm:
Iron Block Iron Heads Add .002″
Iron Block Aluminum Heads Subtract .006″
Aluminum Block Aluminum Heads Subtract .012″
Hydraulic Lifter Adjustment
Adjusting hydraulic lifters can be done basically the same and in many cases both rockers can be adjusted at the same time –just make sure to stop about 20 degrees or so after the intake for that cylinder closes so as not to end up with the exhaust starting to open. Hydraulics require preload not lash so the method is slightly different. Once the rocker(s) in question are ready to adjust, back them off until they are loose enough to rattle. Take the pushrod you are adjusting between your thumb and forefinger and spin lightly (don’t hold it too tight or apply up or down pressure)while slowly tightening the adjuster. As SOON as you feel a slight drag, you are at zero lash – you must hold the pushrod lightly to feel this. Once you have zero, you must turn the adjuster enough to preload the lifter properly. The old “turn it ½ turn” method may or may not be correct. You don’t want them too loose as you run the risk of pounding the retainer ring out of the lifter body or at the least having noisy lifters. Too tight and your valves may not fully close and will surely float at an early rpm- you may have witnessed this before if you ever were around a performance car that ran like heck , but layer over severely / backfired at a relatively low rpm. Most performance lifters have a specified preload which you can get from the manufacturer if you don’t know. Many are less than ½ turn. Your adjusters are generally fine thread fasteners, and move a certain part of an inch per revolution. Below is a list of standard sizes and how far they move per turn- Find the figure for your adjuster size and divide it by your specified preload. Example:
Your lifter preload is spec’d at .008 -.012 and you have 3/8 adjusters . Divide .0419 by.008=5.24. Divide .0419 by.012= 3.49 Put a 1 over that or 1/5.24 - 1/3.49 or about 1/5th to 1/3rd turn is your specified preload.
Adjuster Size Travel /Turn
5/16 -24 .0419
3/8 -24 .0419
7/16 -20 .05
It is ok to use the specified figure for cold fire up, but expect to readjust hot to get it perfect. Also keep in mind that new equipment will wear in and you will probably need to readjust a couple times in the first few hours of use before they “take a set”.
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