Lawn Mower Valve Adjustment Symptoms & Required Tools

A well-maintained lawn mower is essential for keeping your yard looking neat and tidy. However, sometimes even the most reliable mower can experience issues. One common problem is poor valve adjustment, which can present through several noticeable symptoms.

This article will explore the various symptoms of poor lawn mower valve adjustment and their consequences.

What is the Need of Valve Adjustment of any Lawn Mower?

Lawnmowers are essential tools to keep your yard tidy and healthy. However, maintaining their proper functioning is not always easy. One of the key aspects that can make or break the performance of any lawn mower is the valve adjustment.

Valves are crucial engine components responsible for regulating air and fuel flow into the combustion chamber and allowing exhaust gases to escape. If the valves are not adjusted correctly or worn, they can interfere with fuel consumption and power output and cause engine damage.

Strange engine noises, decreased power, and uneven performance can detect a poorly adjusted valve. Therefore, ensuring that your lawn mower’s valves are regularly checked and revised by experts to ensure optimal performance and long life is crucial.

Here are some of their importance and why you need to fix any problems related to it:

  • Accurately setting the opening and closing times of your valves is critical.
  • When valve adjustment is correctly established, you can expect peak performance from your mower and improved fuel efficiency.
  • Additionally, proper valve readjustment allows room for thermal expansion. Therefore, make sure your valves are adjusted just right for optimal results!

What is the Tool Used to Adjust Valves?

Valve adjustment tools are designed to help you precisely adjust the clearance of your engine valves. These tools allow you to properly check and adjust the valve clearance to ensure optimum performance and prevent any engine damage.

Valve adjustment tools are typically hand-held or mounted onto a stand for easy use. The most common type of valve adjustment tool is the feeler gauge, which measures the gap between the valve stem and its seat. Feeler gauges are usually sold in sets that include several different sizes so that you can choose the one that best fits your engine.

  • Measuring range: 0.05 – 1.00 mm
  • Blade length: 100 mm

Scope of supply: Feeler gauge with 13 blades and nickel-plated shell in a transparent plastic pull-out box

Top 5 Lawn Mower Valve Adjustment Symptoms

Lawn mowers, like any other machine, can develop issues over time, especially if not cared for or maintained properly. These issues can lead to various symptoms that indicate a need for adjustment. Below are the five most common symptoms of poor valve adjustment on your lawn mower.

1. Noisy Engine

If your lawn mower’s engine has started to make unusual noises, such as rattling or knocking sounds, it may be due to improper valve adjustment. The engine’s valve clearances may be too tight or too loose, causing the valves to operate inefficiently. Poor valve adjustment can lead to increased wear and tear on the engine’s components, and it is essential to address the issue promptly for smooth and effective operation.

2. Hard Starting

A properly adjusted valve ensures that the engine starts with ease. However, if the valve clearances are incorrect, you may notice that the lawn mower takes several attempts to start or perhaps doesn’t start at all. This can cause frustration and delays in getting your lawn maintenance tasks done.

3. Hard To Pull Starter Cord

If the starter cord on your lawn mower is suddenly difficult to pull, it could be a symptom of poor valve adjustment. When the valve clearances are incorrect, the piston may not move as smoothly within the engine’s cylinder, which can cause increased resistance and make it difficult to start the mower.

4. Power Loss And More Fuel Consumption

One consequence of improper valve adjustment is a significant decrease in the engine’s overall power output, accompanied by increased fuel consumption. This combination of symptoms can make mowing your lawn a more time-consuming and ultimately more expensive task.  By adjusting the mower’s valves correctly, you can ensure optimal engine performance, saving both time and money.

5. Lack or No Compression

Proper valve clearance is crucial for adequate compression within the lawn mower’s engine. If the valves are poorly adjusted, the engine may lose compression, leading to decreased power and the possibility of the mower becoming completely inoperable. Addressing this issue by changing the valves will restore the necessary reduction and help your lawn mower perform at its best.

Fixing Lawn Mower Valve Adjustment Symptoms: Step-by-Step

Fortunately, most lawn mower valve adjustment issues are relatively easy to resolve. In most cases, the problem can be fixed with simple tools and basic instructions. Here is a step-by-step guide for correctly adjusting your lawn mower’s valves:

Step 1: Prepare the Mower

First, ensure you have all the necessary tools and parts for performing the valve adjustment. Before beginning any maintenance, ensuring the mower is in a safe working environment is also essential—ideally, a flat surface with no obstructions or potential hazards.

Step 2: Access The Valve Chamber

To access the valve chamber, follow these steps.

  • Start by removing the spark plug and turning off the gas tap.
  • Then, remove the exhaust muffler, crankcase breather, and rocker cover.
  • Try to preserve the gaskets since you can reuse them if they’re in good condition.

Step 3: Check The Valve Action

Ask for help from a friend and pull on the starter cord to rotate the engine slowly as you observe both valves open and close.

Step 4: Check The Pushrod Action

If it is an Overhead Cam Unit (OCU), no pushrod will be installed. However, on other engines, turn the engine slowly to check that both valve springs are being compressed in turns; also, check that the pushrods are secured in place with no bends or damages.

Step 5: Adjust The Valves

Set the intake valve in line with the carburetor and the exhaust valve in line with the muffler. Rotate the engine slowly until it is at Top Dead Centre (TOD), where you can adjust the valves. For each valve, measure its gap setting using a feeler gauge and alter if necessary by releasing the locknut on top of it. Turn the adjusting nut 1/8th clockwise while assessing clearance; when correct, tighten up the locknut, then reattach parts in reverse order.

What Do Lawn Mower Engine Valves Do?

Valves serve to make combustion complete by maintaining an airtight piston chamber. They open and close to facilitate the flow of fuel/air vapor and exhaust gasses; their function is as follows:

  • The intake valve opens when the piston moves up, allowing the gas/air mixture into the chamber. When it reaches the top of its travel, it closes, making an airtight cylinder.
  • Combustion then occurs, followed by the forced downward motion of the piston due to air tightness. At the cycle end, the exhaust valve opens and expels combusted gasses out of the exhaust, closing afterward and resuming cycling.

Pushrods or a camshaft directly activate valves by pushing on rockers that control valve position with space (valve lash) between them and the tip.

Valves May Need Adjusting When The Engine Is Hard To Start

If you have checked the most prominent issues, including;

  1. Inadequate or insufficient gas.
  2. Faulty sparkplug of lead.
  3. Clogged air filter.
  4. A faulty or gummed-up carburetor.
  5. A faulty coil.
  6. A bail lever/ignition fault.
  7. Bad flywheel timing.

Final Thoughts

If you have ruled out all of the above potential causes and your engine is still hard to start, then it’s likely that your valves may need adjustment. It is essential to periodically check and adjust your lawn mower’s valves to ensure optimal performance and extended life expectancy from the machine.

Most valve adjustment tasks can be completed without professional help following a few simple steps and using essential tools. Be sure to check the engine’s manual for specific instructions on adjusting your lawn mower’s valves.

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