How To Repair Lawn Mower Engine (Helpful Guide)

push lawn mower repair

Who says that you have to be a mechanic to fix a lawn mower engine? With the help of the following steps, you will have a properly functioning lawnmower engine without spending a dime on a mechanic.

Step 1: Disconnecting the Spark Plug

remove the spark plug of lawn mowerStart by disconnecting the spark plug. This will prevent the lawnmower from starting abruptly so you can work on it without any hazardous outbreaks.

Make sure to wear durable gloves and safety goggles in case of metal pieces, gasoline residue or dirt which may cause an infection. Don’t hold any pieces of metal to the spark plug or else you will likely suffer from a painful shock.

Step 2: See Spark Plug Condition

See spark plug conditionTake a good look around the spark plug before disassembling


the engine to figure out what is the actual problem.

The spark plug could be worn out, bridged, melted, overheated, coated with ash/oil or affected by carbon deposits, preignition, high-speed glazing, detonation or mechanical damage.

Identify what situation the spark plug is in and then determine which action to take to properly fix your lawn mower engine.

Spark Plug Condition Chart

Spark Plug Condition chart

Step 3:

Step 4-minAs the most common ignition system is the magneto ignition system, make sure there is a small gap, about the thickness of a gift card and no more, between the magnets in the flywheel and the magneto itself.

When the machine is started, the flywheel turns. There are two “teeth” on the starter to turn it, and the cord will rewind as soon as the brake is disengaged.

Step 4:

Step 4-min

It is very common to mess up while trying to remove a flywheel. But when done properly, it’s easy! There is a nut that holds the flywheel so strongly that it can only budge by blocking the rotation of the crankshaft while holding the nut on the blade with a wrench.

You can also try blocking the rotation of the blade. Don’t try to tamper with the flywheel as it can cause the teeth to break off.

Once the nut is removed, gently detach the flywheel with a crowbar and put it to one side safely. The flywheel is marked to indicate which way to put it back into place correctly.

Step 5:

Step 5-minUsually, with engine mishaps, the carburetor is likely to be the pest of the problem. It is crucial that the carburetor stays clean, but it is tiring to do so.

If it is gunky from gasoline, place the metal bits in a container of gasoline overnight and no longer.

Examine the float for issues and soak it in water to make sure there aren’t any holes. The float valve should be clean to move without resistance. See if the carburetor is clogged, as this is a very likely issue.

If it is, don’t fret, just run a wire through it and use a flashlight to get the hard to reach spots.

Step 6:

Check if the hole in the gas cap is clogged, only if your mower has this feature. Gently screw off the cap, run a small wire to clean it if it’s clogged and see if the engine starts.

Check the gas tanks filter if you see gasoline leaking from the main line. Clean the gas tanks filter with slight brushing.

If this doesn’t fix the issue, then run a pipe cleaner or something of that sort through the line. Do this until the pipe cleaner comes out clean.

For other engines, push primers should be cut-free and the air hole should be open to creating the correct air-fuel mixture for the engine.

Step 7:

Step 7-minIn a four-stroke engine, there are two valves; the intake valve which pushes the air-fuel mix into the combustion chamber and exhaust valve which releases the carbon monoxide and remnants of the combustion.

These valves are controlled by a camshaft which can collect gunk. This can be cleaned by a valve cleaner or simply by hand. Sometimes the valves can have scratches or leak oil, which indicates that you’re not changing its oil regularly.

If the valves are chipped badly or don’t work properly, then you have no choice but to change the valves with new ones.

Step 8:

Although the spark arrestor is not a very crucial part of a lawnmower engine, it is required by law on all outdoor engines. It prevents fires by catching sparks. Most spark arrestors cannot be opened, so you will need to use wire to clean it out of any possible blockages.

Step 9:

Step 9-minRemoving the piston is very dangerous as it means you will have to separate the two halves of your lawnmower engine. It is not recommended of course, but if you do, be sure to take proper precautions.

Once you have separated the two halves of the engines cautiously, disconnect the piston from the crankshaft and push the piston out through the combustion chamber. Your piston is fine if you see gaps in the rings are lining up as you pull the piston out of the engine.

Align the piston ring gaps at about a 90-degree difference so that the oil cannot spill through. Also, check the cylinder walls for scratches which could be letting in the oil. If you still haven’t found the problem, then it means your piston rings have gone bad.

Use a ring compressor or two pairs of pliers to remove them. But be careful to not put the wrong ring on one of the groves! After placing the rings, scatter the gaps of the rings at a 90-degree difference and add a little engine oil, so they work smoothly.

Put the piston back in using the markings given, so you don’t put it in the wrong direction. Squeeze the rings a little if you have to in order to get the piston into the cylinder. Then just screw everything back together! Easy as that.

If you tried these steps and nothing seems to work, then it’s time to throw out the old mower and get a new one. Starting afresh doesn’t hurt, right? Hope this helped you a pinch!