How To Adjust Lawn Mower Valves (Expert Advice)

If you own a lawn mower, you know how important it is to keep it running at its peak performance. 

Lawnmowers do not come with an instruction manual, so it can be tricky to know exactly how to adjust your machine’s valves and other parts. 

However, with a little knowledge of what you’re doing and some gentle handiwork on your part, you can keep your lawnmower running like new for years to come!

How to Adjust Lawnmower Valves
How to Adjust Lawn Mower Valves
Regular valve adjustment is necessary for optimal performance of a lawn mower engine.
Adjusting valves can be complex, but following the manufacturer’s instructions and using the right tools can make it easier.
A feeler gauge is a must-have tool for valve adjustment.
Proper valve adjustment can prevent engine damage and reduce emissions.
For best results, also adjust your lawn mower throttle cable, deck, and cutting height.

Check Engine Speed At 3,000 Rpm

To check your mower’s engine speed, you’ll need to turn the throttle all the way up and then check your engine’s RPM. Locate this number on your mower and write it down somewhere (you’re going to need it later).

If your mower is running too fast or too slow, follow these steps:

If your engine is running fast, adjust the idle screw counterclockwise. This will make it easier for you to keep control of how fast or slow the blade spins once you start cutting grass. 

The ideal setting for most lawnmowers is 3,000 RPM when they’re idling without any load attached to them.

If your engine is running slowly, adjust the idle screw clockwise until its optimal speed has been reached—usually between 1,100 and 1,200 RPM per minute at a 3/4 throttle position when no load is applied (this means cutting grass). 

This might take some practice before getting used to what feels right; however, once achieved it should stay consistent even under full load conditions such as when mowing tall grasses.”

When adjusting your lawn mower, don’t forget to adjust the throttle cable as well to achieve the best results. Check out our guide on how to adjust lawn mower throttle cable to learn more.

Warm The Engine

Warm the engine for 5 to 10 minutes before you begin to adjust the valves. This will make it easier to get an accurate reading on compression and help prevent damage from cold metal surfaces rubbing together. 

You can do this by starting your lawn mower and letting it idle until all of its parts are warm, or use a heat gun on the high (but not too hot) setting for about 2 minutes on each cylinder head.

Warm Up Engine Before Adjusting Valves

Start your lawn mower and let the engine warm up for 5-10 minutes.
Turn off the engine and remove spark plug wire.
Refer to the operator’s manual for the correct valve adjustment settings.
Use a feeler gauge to check the clearance between the valve stem and rocker arm or cam.
Adjust the clearance as needed using a wrench or adjustable pliers.
Recheck the clearance with the feeler gauge and adjust again if necessary.
Replace the spark plug wire and start up the engine again to make sure everything is running smoothly.

The table above outlines the steps for warming up your lawn mower engine before adjusting the valves. This step is critical to prevent damage to your engine and ensure an accurate reading on compression. The table provides a detailed process for warming up the engine and adjusting the valves, including using a feeler gauge and referring to the operator’s manual for the correct settings.

Measure Compression

To measure your compression, you’ll need:

  • A compression gauge
  • A screwdriver to remove the spark plug wire and spark plug (I would recommend an 8mm socket wrench)
  • Another person to help you hold the engine steady while testing (this will give more accurate results)

Is your lawn mower deck uneven? This can cause uneven cuts and an unsightly lawn. Learn how to adjust it properly by checking out our guide on how to adjust lawn mower deck.

Adjust Valve Clearance

Adjusting the valve clearance is a simple process that can be done using the right tools and following a few steps. 

Keep in mind that your engine may require specific tools for this process, so be sure to consult your owner’s manual before you get started.

Loosen the screws holding down each cap on top of the valves. The cap should pop off easily once it’s loose enough.

Measure the gap between each plug and seat (or valve stem) using a feeler gauge tool or a ruler with millimetre markings, which will help determine if they’re too high-or low-clearance settings (excessively open). 

This measurement will vary depending on what type of mower you own—Briggs & Stratton engines have an optimal gap around 0.018 inches (0.46 mm), while Kohler models usually have valves set at 0.020 inches (0.52 mm) apart from one another.

If there are any gaps higher than 0..016 inches (0..41 mm), then you need to tighten them! Tighten each screw until they’re snug but not over-tightened—you don’t want them snapping off as soon as you start up next time.

If there are any gaps lower than 0..016 inches (0..41 mm), then loosen those screws slightly until they’re just above flush with their respective holes.

Then go ahead and reattach all four caps over top of each pair of valves before starting up again!

Unlock Points Cam

In order to adjust the valve lifters, you’ll need to first unlock the points cam. Turn the points cam counterclockwise until it stops. 

The engine must be hot enough in order for this step to work otherwise it will not turn smoothly and will likely bend. If you feel resistance while turning the point cam, don’t force it!

If you’re looking to add more grass to your lawn, it’s important to do it correctly to ensure successful growth. Follow our guide on how to add grass to your lawn for tips on the best methods to use.

Measure Valve Clearance

The next step is to measure the valve clearances. To do this, you’ll need to remove the spark plug and then measure with a feeler gauge. 

The goal here is to have as little resistance as possible when you insert the feeler gauge between two rocker arms on each cylinder.

To make this easy, let’s write down what we’re going to do:

  • Remove the spark plug from the engine block
  • Measure valve clearance using feeler gauges of different thicknesses
  • Replace the spark plug before starting the engine

Measuring Valve Clearance

Locate the valve cover and remove it using a wrench.
Remove the spark plug wire to prevent the engine from accidentally starting during the valve adjusting process.
Turn the engine slowly by hand until the valve of interest is fully open.
Use a feeler gauge to measure the clearance between the valve stem and rocker arm or cam.
Compare the measurements to the specifications in your engine’s repair manual.
Adjust the clearance as needed, using a wrench or adjustable pliers to move the rocker arm or cam follower.
Replace the valve cover and spark plug wire when finished.

Adjust Cam Timing

  • What You Need to Get Started

Before you start, there are a few items you should have on hand. These include:

  • A manual for your lawn mower model
  • A socket wrench and socket with extensions (a ratchet will work if you don’t have extensions)
  • A flat-head screwdriver or another thin object like this one (to help turn the engine pulley)

Adding topsoil to an existing lawn can be a great way to improve its overall health and appearance. Check out our guide on how to add topsoil to an existing lawn to learn how.

Replace the Flywheel Key

If your lawn mower has a flywheel key and you need to replace it, there are a few things to know about how these keys work. 

First of all, the flywheel key is essentially a piece that fits into one side of your mower’s flywheel it helps lock it in place so that it can’t move when you’re cutting grass. You may also see them called “flywheel bolts” or “flywheel nuts.”

To replace this part on most models, follow these steps:

Remove any blades from the mower that might be attached at the moment; they’ll get in the way while working on this part of your machine.

Unscrew any bolts holding down any other parts such as air filters or oil filters if necessary before removing them completely (following manufacturer instructions for specific maintenance instructions).

Remove any screws holding down wires connecting various electrical components as well (also following manufacturer instructions).

Pull out whatever levers are used for adjusting height settings so that your wheels are fully raised off the ground; set aside somewhere safe where they won’t get damaged during work being done here today! 

If there aren’t any levers involved then just lift off the wheels by hand instead, but do not turn over the engine yet!

Turn The Flywheel Until A Mark Is Visible On The Piston Top

The next step is to turn the flywheel until a mark on the piston top is visible. This mark will be used later to align everything back into place once you are done adjusting your valves.

Once you have identified this mark, lock in the flywheel with a wrench (leave it loose enough for turning, but tight enough that it does not move).

Adjusting your lawn mower’s cutting height is important for maintaining a healthy and attractive lawn. Check out our guide on how to adjust lawn mower cutting height for tips on the best way to do it.

Set The Engine To Top Dead Center For Tdc For Cylinder No. 1

To set the engine to TDC for cylinder No. 1, you will need to follow these instructions:

The first step is to remove the spark plug wire from its cable clamp and then rotate it so that it’s pointing upwards, away from the engine block. This ensures that there’s no chance of getting shocked while working on your lawnmower.

Next, turn your ignition key all the way off until you hear a click noise coming from inside your lawnmower’s engine bay. 

This means that the electric fuel pump has been turned off as well—important because if you don’t do this step properly, petrol fumes could fill up in either one of two places: inside your car or outside where you’re working on changing out those spark plugs! 

If not done properly (which can happen), those fumes could become combustible without warning during re-assembly later on downtime – which could cause serious injury/death if ignited by accident.”

Lock In The Points Cam

  • Make sure the points cam is locked in place.
  • Turn the flywheel until a mark is visible on the piston top.

That’s it! You’re about to learn how to adjust your lawn mower valves, and now you’ll never have to pay someone else for this task again.

Install Spark Plug Wire And Sheath

Now that the spark plug wire is off, you can remove the spark plug.

Use a spark plug socket to loosen and remove the spark plug.

Remove the old spark plug from its socket, then put it in your hand and inspect it for dirt and grime. If it’s dirty, wipe it down with a rag or paper towel until it’s clean and dry before replacing in its home on top of your engine block (this will ensure there will be no problems later).

Keep Your Lawn Mower Running Like New By Adjusting Valves Properly

Your lawn mower’s engine is a finely tuned machine that requires regular maintenance to keep running smoothly. 

One of the most important parts of maintaining your lawn mower is adjusting the valves. Valves regulate airflow into and out of the cylinders, so when they’re loose, too much air can escape from them and cause problems with how well your engine runs.

To adjust your valves:

Check if any bolts are loose or missing before you start working on it; you don’t want to have to stop in the middle of an adjustment because you forgot something!

Read over any instructions or warnings that come with your specific model’s manual before adjusting anything (it never hurts to be safe). 

Some engines require certain tools for adjusting valves; if yours does not specify these tools on its manual then try using a pair of needle-nose pliers instead). 

If you’re unsure about what kind of tools will work best for whatever model mower you own then call around until someone gives good advice or directs you towards another resource where they might provide answers instead).


That’s it! You’ve now got all the knowledge you need to adjust your lawn mower valves. With a little patience and practice, you can keep your lawn mower running like new for years to come.