Setting valve lash can be a daunting task for many people. However, it is not as hard as you think! This blog post will provide step-by-step instructions on how to set your valve lash correctly. We’ll also go over the benefits of setting your valves correctly and what happens if you don’t.

The first step is to gather the necessary tools. You will need a wrench, torque wrench, and feeler gauge. The next step is to find Top Dead Center (TDC). This can be done by either using a piston stop or by looking at the timing marks on the camshaft. Once you have found TDC, loosen the intake manifold bolts and remove the manifold.

Now it’s time to set your valve lash! Start by checking your valve clearance with the 0.006″ gauge. If the clearance is not within spec, then you will need to adjust it. To do this, use the adjusting screws on top of each rocker arm to lengthen or shorten the pushrod until you achieve proper clearance.

Once you have set the clearances, replace your intake manifold. When replacing the rocker arms, tighten them in a star pattern to avoid warping of the heads. Now get out that torque wrench and tighten all bolts down to spec! Finally, double check all your work with another cylinder leakdown test… 

just because it passed before doesn’t mean it’ll pass after tightening everything up! If there are any leaks or if something feels wrong then go back and fix those problems before driving around town on this thing; safety first right? Good luck setting valve lash!

What is valve lash and why is it important to set it correctly

Valve lash is the clearance between the rocker arm and the valves when the engine is running. The amount of clearance determines how much in control you are in your application. A larger gap would mean less in control, but more power while a smaller gap puts you in greater control at the cost of power.

What should we set it to?

Different manufacturers recommend different things for their performance applications. Generally, we like to see .006″ – .008″ on stock GM engines and .002″-0025 (stock) on modified and high performance GM engines and small aluminum cammed aftermarket roller rockers. 

If you want all out race camshafts that turn 8500+ rpm you’ll probably be running .001″ lash (this is not advisable for most street applications). You can run tighter with hydraulic roller cam shafts than with flat tappet because the cams are designed to operate at contact points real close to each other without any lifter/ pushrod interference.

Where does it come from?

-Generally, the lash is determined by how tight or lose your rocker arms or rocker ratio is. The less overhang on the tip of the valve you have, the more control you will have but it comes at a price; reduced rpm potential. 

How do I keep from making a mess? -It’s pretty simple really. Just use a feeler gauge and find where your lash is on the metal tip of the rocker arm. Then, take some 600 grit sand paper or Emory cloth and clean it up just enough to get rid of any nicks or burrs.

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General guidelines for setting your valves are as follows: A .006″ lash with stock GM engines is generally good for up to 4000 rpms with roller rockers. If you are running hydraulic flat tappet cams with the above mentioned lash, you will probably be able to achieve 5000 rpms with no problems at all. As you increase valve lift over .500″, reduce your lash accordingly. At least that’s the way we do it here at BHR Street Rods & Racing Engines!

How to check your valve lash before you start?

First off, why is it important to have the correct valve lash when you build your V12? It’s important to have the correct lash in order to get the most power from your engine, and also with the correct lash, the engine will run smoother too. The following is taken directly out of Builders Tips & Tricks (a must read IMO)

“All 12-cylinder engines with overhead camshafts need what is called “valve lash”, in other words a very slight amount of clearance between the valves and their respective tappets. This small clearance allows for expansion of the metal parts due to temperature changes, etc., without actually having them touch each other. Engines that do not have this slack are quite prone to destroying valves quickly when hot because there is correct valve lash?

If you have excessive lash this may mean that the valves are not seating correctly and will affect how much compression you get from your engine.

Excessive lash can also cause a loss of power because the air/fuel mixture which should be ignited in the combustion chamber instead leaks past the poorly seated valves and triggers the exhaust valve before any useful work has been done! 

And lets face it we all know what a loss of power means… sometimes there’s nothing like a nice cup of tea and having to start again (been there, done that many times!). The last thing you need when building an engine is for this to happen. 🙁 engine.

One of the most important parts of setting up your engine correctly is having the correct valve lash. When you set the valve lash, you adjust the gap between the cam follower and the cam lobe on that cylinder’s overhead valve (OHV) or in-line valve (OHC). On an OHV V8, a single cam lobe operates both valves for each cylinder. 

On a dual-valve OHV V8 such as those found in GM cars from 1955 to 1996, there are two separate cams and followers for each pair of cylinders – one for intake valves and one for exhaust valves. In any case, every time an overhead valve opens or closes it releases pressure from or adds pressure to the combustion chamber. 

The steps involved in setting the valve lash on your engine

are very straight forward, however getting the lash set correctly can be tedious at times.

The process for valve lash adjustment is always performed with the engine cold. You will need an accurate feeler gauge to measure the gap between the rocker arm and the valve stem in order to set the correct lash.

An adjustable wrench is required in most cases to adjust the rocker arms down on top of each valve stem, however there are some applications where a flat blade screwdriver or needle nose pliers can be used instead.

A dial indicator is very helpful when trying to determine when all 4 valves have been adjusted properly when doing a complete overhaul on an engine that has already had its valves adjusted in previous years.  If you are just checking the lash on your engine to see if it needs adjustment, you can skip the dial indicator step.

To check the lash with a dial indicator, you will need to remove all 4 rocker arms and measure the gap between the rocker arm pad and the tip of each valve stem with your feeler gauge.  The gap should be exactly 0.020″ (twenty thousands) for best performance and extended valve life.

When adjusting your valves, having vacuum advance disconnected from your distributor or unplugged from under the dash would be beneficial due to ease of cranking compression while doing so. The timing stays locked in place with your distributor on the base timing mark, which is a good location for initial start up.

Every engine will be a little different on how much valve lash they possess from the factory.  Typically the smoother running engines have less lash then those that have more vibration throughout operation of the vehicle.  By having some amount of clearance between each valve stem and rocker arm allows for the valves to open and close without hitting either piece of metal as it rotates within its bore. 

The opposite would result in your valves being constantly hit every time you crank the engine resulting in early failure or at least prematurely wearing out what ever set up you may be working with.

When should valve lash be set?

Engine valve lash should be adjusted at the first oil change on a new engine. On Cat Marine Engines, the first oil change is typically recommended at 250, 500 or 1000 hours. A valve lash adjustment is critical because the valves of a diesel engine play a key role in the combustion process. 

The types and time intervals for adjustments to be made after an initial setting are determined by such factors as engine type (wet liner or dry liner), number of cylinders and engine speed range (idle, low speed, medium speed and high-speed).

So when should valve lash be set?

The interval for all engine manufacturers is typically at the first oil change (oil and filter) on a new diesel engine. How much time or hours after an initial setting will depend on: 1) what type of engine it is (wet liner vs. dry liner), 2) how many cylinders it has and 3) what its speed range (idle, low speed, medium speed or high-speed). 

The general rule of thumb is that there are four basic types of engines used in marine applications: 4-cycle diesels, two stroke diesels, steam turbines and gas turbines. All types have wet liners except for gas/turbine engines. Wet-liner engines typically have full flow oiling systems which require an oil and filter change at each engine overhaul, such as Cat® marine diesel engines. Dry liner engines use a separate reservoir for the cylinder head and cylinder lubrication, such as Cummins® QSM11® two-stroke diesels. 

The valves in dry liner engines do not need to be adjusted after initial installation because they don’t normally ever need adjustment.

Three other things determine when valve lash should be set: 1) the frequency of the oil and filter changes (it is recommended to follow your operator’s manual recommendations), 2) what type of fuel is being used (if using biodiesel or low sulfur fuels this may decrease the time between oil/filter changes) and 3) the type of service your engine operates in (e.g., fresh water vs. saltwater or working hard such as with a trawl winch).

The most important thing to remember if valve lash is not set at initial installation and later requires adjustment is to follow the “one size up, one-half turn back” rule. The first step for all engines is to set the lash at 0.020 inches (.5mm) less than the minimum required by your engine’s manufacturer recommendations. 

This should provide enough clearance to account for thermal expansion without requiring a re-adjustment during a normal oil change cycle that follows your operator’s manual recommendations on how often an oil and filter change is performed. Following this tip may eliminate the need for you or your mechanic to be present for this initial adjustment.

If the lash setting checks out, but it’s found that after many hours of operation the lash setting is too tight at 0.020 inches over minimum requirements, then an adjustment will be needed. The manufacturer recommendation is typically that each time oil and filter service is performed, lash should be set one size up (.020) from minimum specifications given in the engine’s operator manual.

So if your lash was initially set at 0.010 inches (.25mm), then after oil/filter changes (assuming frequency of oil/filter changes matches your operator manual recommendations) the next valve lash setting would be 0.030 inches (0.75mm). 

Again, once checked with a straight edge and feeler gauge, valve lash should be adjusted by rotating the adjuster bolt in a clockwise

Remember that valve lash is critical to ensure performance and longevity of your diesel engine. Also remember that if not initially set correctly, each time oil and filter changes are performed thereafter (typically every 100 hours) the valve lash should be checked and corrected as necessary under one size up/one-half turn back rule until final assembly or overhaul of an engine where all parts will come together for “final” adjustment. 

Be sure to keep track of when another inspection needs to occur as well as what your initial sets were as they may need to be adjusted again a

Lash Timeline for Adjustment (General Rule of Thumb):

0 – 250 hours – 0.010″ (initial setting)

250 – 500 hours – 0.015″ (used during oil changes at this point, then set again to .010″ after 1000 hrs or 1 year)

500 – 1000 hours or 1 year- 0.025″ (adjusted each time oil and filter are changed which is typically every 100 hours)

1000+ hours or 11th year onward ->TBD(adjusted upon engine rebuild by factory technician based on service history).

Oil & Filter Change Schedule for Marine Engines: 

NOTE: Daily inspection is required by ABYC standards to ensure intrusion does not result in a hazardous condition.

0 – 50 hours – Not Required (unless oil is visibly discolored)

50 – 150 hours – Oil and filter must be changed at least once within this time frame (if using standard or lower viscosity oils, then filters may need to be changed more frequently). If using higher viscosity oil such as a 15W-40 engine oil, the filter may only need to be changed after 100 hours. Replace strainers as well. 

150+ Hours – Every 100 Hours / 1 year interval thereafter (oil and filter must be changed according to your operator’s manual recommendations)

What happens if valve lash is too loose?

If the valves are allowed to leak excessively, then this will result in loss of performance and can cause cylinder damage or even failure.

For example, when a camshaft fails, it usually results in the lobe being ripped away from the shaft. This causes severe damage because it requires removing the cylinder head in order to replace the camshaft.

The lobe is usually ripped away from the shaft because the loose lash allowed the valve springs to collapse while spinning at high speed, which caused them to break off. This can result in damage or even failure of other components that are directly attached to this part, such as piston heads.

How do you set valve lash on hydraulic lifters?

Valve lash is an important part of hydraulic lifters. It determines how much oil can flow through the valve and into the lifter to keep it properly pressurized, while also controlling the amount of pressure on the cam lobe during operation. Setting valve lash requires a basic understanding of hydraulics, but if you are unsure about what type of valves you have in your system, consult with a mechanic before proceeding.

Take a look at the picture above. On this car, we have hydraulic lifters and conventional valves with shim stacks on both ends of each valve stem – one for lift (taller stack) and another for preload (shorter stack). Each shim is labeled to identify it as either “L” or “P” to indicate which end is for preload.

Setting the valve lash on hydraulic lifters consists of two steps: setting maximum and minimum lash. The picture above shows a typical set-up that works well with shim stacks, but there are other methods available as well depending on your particular system setup (and experience). Each type of system is a little different, and it’s important to follow the guidelines set by your particular manufacturer.

Step #0:

Prepare Your Work Area Before you start setting valve lash on hydraulic lifters, make sure that you have everything ready to go so that nothing gets in your way during this process. We like to use an old towel and a marker to draw right on the valve cover. That way we can keep track of what goes where without having to mark everything up with grease or oil!

Step #1: 

Remove Valve Covers, Clean Valves Before you start setting the valves, remove your valve covers (if necessary), clean off all dirt and grime from the valves and valve seats, and check for any damage that may need to be repaired.

Step #2: 

Locate Your Hydraulic Lifters Now that your work area is ready, it’s time to start locating the hydraulic lifters. On most engines, they will be located on the top of the engine near the camshaft. If you’re not sure where they are, take a look at your engine diagram or consult with a mechanic to 

Step #3:

Identify the Valve Lash Settings Now that you have found your hydraulic lifters and identified their location on the valve cover, it’s time to identify the lash settings.

Step #4: 

Identify the Top and Bottom of the Lifters Next, use a marker to write “T” or “B” on each lifter that corresponds to its top (towards cam) or bottom position. For example, in this picture we are writing T for topside so that we can easily identify them when we are done.

Step #5: 

Measure and Mark the Maximum Lash Now that you have everything marked, it’s time to measure and mark the maximum lash setting. On this particular valve cover, there is a ridge around the outside edge which makes it easy to find. If your valve cover doesn’t have a ridge, you can use a straight edge to find the maximum lash setting.

Step #6: 

Measure and Mark the Minimum Lash Now that you have found the maximum lash setting, it’s time to measure and mark the minimum lash setting. This is typically done in the same area as the maximum lash setting, but on the opposite side of each lifter.

Step #7:

Remove Valve Lift Now that you have identified all your settings, it’s time to remove the valve lifte from its seat by gently prying off one corner with a flat head screwdriver or similar tool. For this particular engine, we are working on an engine with shim stacks, so we need to hold the lifter up and away from the valve while maintaining pressure on it. This keeps hydraulic fluid in the system and prevents damage to internal components.

How do you calculate valve lash?

  • The first thing is the cam duration at 0.050” lift, measured in crankshaft degrees of rotation per degree of intake and exhaust lobe travel (the same units as using a degree wheel). This number can be found in the cam card. Let’s say it is 240 degrees of intake and exhaust lobe travel per degree of crankshaft rotation, with 0.050″ lift at 36 degrees (degrees before top dead center – BDC) on both valves being zero lash point for this example.
  • The second thing is the static valve clearance. This number can be found in the cam card, too – it’s usually expressed as a pressure (in psi or bar), and you need to multiply by 0.01 inch (or 0.25 millimeters) per unit of measurement to get our lash value at zero lift point:

1: for intake valve: 0.01 x 23 psi = 0.23 inch (0.60 millimeter)

      2: for exhaust valve: 0.01 x 27 psi = 0.27” (0.69 mm).

  • The third thing is the static piston to valve clearance, measured in crankshaft degrees of rotation per degree of valve lift. This clearance can be found in the engine’s shop manual and is usually given as a range (e.g. – 0.004-0.008 inch).

To calculate valve lash, you need to know three things:

  • The cam duration at 0.050″ lift, measured in crankshaft degrees of rotation per degree of intake and exhaust lobe travel
  • The static valve clearance
  • The static piston to valve clearance, measured in crankshaft degrees of rotation per degree of valve lift.

Next, let’s take a look at how to determine the lash value at zero lift point for both intake and exhaust valves for our example camshaft.

  • The static piston to valve clearance (crankshaft degrees of rotation per degree of valve lift) is given as 0.004-0.008 inch in the shop manual, so we’ll take an average value of 0.006 inch.

To calculate valve lash, you need to know three things:

  • The cam duration at 0.050″ lift, measured in crankshaft degrees of rotation per degree of intake and exhaust lobe travel
  • The static valve clearance 
  • The static piston to valve clearance (crankshaft degrees of rotation per degree of valve lift), given as 0.004-0.008 inch in the shop manual, where we have taken an average value of 0.006 inchL=Crankshaft degrees per degree of valve lift: 60/0.006 = 1000 crankshaft degrees per one unit (or “1000” for short)

So, now we know that the lash value at zero lift point for our example camshaft is 1000 crankshaft degrees.

To calculate valve lash:

  • Find the cam duration at 0.050″ lift on the cam card 
  • Multiply this number by 0.050″ to find how many degrees of crankshaft rotation are required to achieve a 0.050″ lift on the intake and exhaust valves 
  • Multiply this number by 1000 (for L) to get the lash value at zero lift point for both intake and exhaust valves: 240 x 0.050 = 120 degrees, 120 x 1000 = 120,000 crankshaft degrees
  • Subtract the static valve clearance from this number: 120,000 – 23 = 119,978 crankshaft degrees of rotation at zero lift point. This will be our lash value zl for both intake and exhaust valves.