Lawn mower rod knock. Humphreys Outdoor Power

Too Much Oil In Lawn Mower? Read Our Easy Fix It Guide!

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What happens with too much oil in the lawn mower? Well, too much of a good thing can be bad for you! Right? Well, the same law applies to lawn mowers and engine oil. An overfilled lawn mower oil tank will lead to performance problems, failed starts, or an oily overflow mess. And much worse!

So, what other engine issues arise from putting too much oil in a 4-stroke lawn mower? And are these issues easy to fix?

Too Much Oil In Lawn Mower

Overfilling a lawn mower oil tank will negatively affect engine performance and possibly prevent the mower from starting. Too much oil in a lawn mower can easily clog the air filter, foul spark plugs, and potentially cause a hydro-lock, which could bend the connection rods in a multi-cylinder mower.

The way 4-stroke oil works in a 4-stroke walk-behind single-cylinder mower or a multi-cylinder lawn tractor is surprisingly straightforward:

  • Lawnmower engine oil lubricates the engine and helps to keep it cool.
  • The oil tank on a lawnmower feeds oil into the crankcase, where it is placed under pressure by the down-stroke of the piston during the combustion process.
  • The air pressure forces the oil upwards to lubricate the piston and cylinder, as well as the crankshaft and con rod (piston push rod).
  • The crankcase has a ventilation valve (breather) that releases pressurized vapor, which forms an oily mist.
  • A rubber hose connects the ventilation valve to the mower’s air filter housing and carburetor air intake.
  • The crankcase vapor passes through the air filter to the carburetor, where it mixes with the gasoline that fuels the engine.

What Happens When You Overfill the Oil In Your Lawnmower?

Too much oil in a lawn mower crankcase causes the vapor released via the ventilation valve to become oil-rich, which clogs the air filter, creating an overly rich air-to-fuel ratio that fouls the spark plugs and causes the engine to smoke and run poorly. Extreme over-oiling will stall the engine.

With too much oil in the mower’s oil tank, an excess amount of oil feeds to the crankcase, effectively reducing the volume (air space) of the crankcase, which increases the pressure in the crankcase during the piston down-stroke.

  • The increase in pressure will force the excess oil through the ventilation valve into the air intake. From there, it will clog the air filter.
  • The oil-rich vapor (potentially pure oil in extreme cases of over-filling) will enter the carburetor and blend with the gasoline that powers the engine.
  • The overly rich air-fuel mixture will enter the combustion chamber and foul the spark plugs, causing the engine to sputter and stall.
  • A severely over-filled lawnmower oil tank (and crankcase) will cause a hydro-lock, where the piston cannot move due to excess oil filling the combustion chamber (between the cylinder head and the piston crown).
  • A hydro-lock has a similar effect to a seized engine – the engine stalls and won’t restart.
  • Attempting to crank the engine of a multi-cylinder mower when hydro-locking has occurred could bend the con rods (piston push rods).
  • Hydrolocked single-cylinder lawnmower engines generally don’t suffer con rod bending.
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How Do You Know If You’ve Put Too Much Oil In Your Lawn Mower?

You’ll know you’ve put too much oil in your mower when:

  • The oil on the dipstick is above the upper indicator line.
  • Excessive smoke emits from the exhaust.
  • The engine runs roughly and sputters.
  • The engine stalls and won’t restart.
  • The spark plug is oily.
  • The air filter is oily.

Can You Put Too Much Oil In Your Lawn Mower?

Yes! You can put too much oil in a lawn mower if you fail to limit the volume of oil poured into the oil tank to the amount specified by the mower manufacturer. And filling oil into the mower directly from a large oil can without checking the dipstick as you fill the tank can lead to over-filling.

Note: Consult your lawn mower owner’s manual for the correct oil volume and grade.

Oil volume ballpark – Lawn mower oil volumes generally vary between 15oz to 20oz, ranging from single-cylinder walk-behind mowers to larger multi-cylinder ride-on mowers.

What Are the Risks of Overfilling a Small Engine With Oil?

The risks associated with overfilling a small engine with oil include the following.

  • Bent con rods – which may require expensive engine repair!
  • Your lawn mower air filter may spoil.
  • Your lawn mower spark plugs risk soiling.
  • Wasted oil – the ultimate sin for thrifty homesteaders!

What to Do When You’ve Put Too Much Oil In the Lawn Mower? Easy Fix!

The best way to fix an overfilled lawn mower is to drain the engine oil from the oil tank, crankcase, and combustion chamber. Remove the air filter and spark plug and clean them to remove all traces of oil. Crank the engine several times with the spark plug removed to purge residual engine oil.

How to Fix a Failed Mower Engine Due to Oil Overflow?

Do you need to fix a lawn mower that’s stopped running due to oil overfilling? Then follow these steps.

Get the Right Tools, Including the Following:

  • A jug or can of the specified oil for your mower.
  • A spark plug wrench.
  • A screwdriver or wrench. These tools help to remove the air filter.
  • A wrench! Wrenches are perfect for removing the oil drain plug.
  • Pliers to remove the ventilation hose.
  • A solvent. It helps to clean the lawnmower spark plug.
  • Detergent! Warm water with grease-cutting soap works fine. It helps to clean the air filter.
  • A plastic funnel.
  • An oil drain pump – but only if the mower lacks an oil drain plug.
  • An oil drain hose – is critical for ride-on lawn tractors.
  • An oil drain pan.
  • A measuring jug.
  • Paper towel.

Troubleshooting Your Lawn Mower – Step-by-Step

  • Disconnect the spark plug boot and remove the spark plug from the engine.
  • Remove the air filter cover and ventilation hose.
  • Remove the air filter.
  • Clean the spark plug.
  • Clean the air filter and dry it with a paper towel.
  • Lightly oil the air filter to prevent it from drying out and perishing.

Drain All the Oil From the Crankcase and Oil Tank – Step-by-Step

  • Remove the oil drain plug (on the side of the engine or under the deck) and drain the oil into an oil drain pan (large mowers may need an oil drain hose to attach to the oil drain valve).
  • Pump oil out of the oil tank (for mowers without an oil drain plug) into an oil drain pan or disposable bottle.
  • Tip the mower on its side with the oil tank cap removed (for mowers without a drain plug). And drain oil from the oil tank and crankcase into an oil drain pan.
  • Crank the engine several times to vent oil vapor from the spark plug hole and crankcase ventilation hose.
  • Let the mower stand with the spark plug, oil drain plug, and air filter removed for 45 minutes to evaporate oil-vapor residue.
  • Refit the cleaned spark plug, air filter, and ventilation hose.
  • Screw in the oil drain plug.
  • Pour the manual-specified amount of oil into a measuring jug (you can DIY a used canned fruit tin or similar).
  • Fill the oil from the measuring jug into the oiling tank via a funnel.
  • Allow the oil to settle for two minutes.
  • Screw in the dipstick and oil cap.
  • Unscrew the dipstick and check the level. Top up if necessary. But don’t go over the upper marker line on the dipstick.
  • Screw on the oil tank cap.
  • Crank the engine. The mower should start.
  • Allow the mower to idle for a few minutes.
  • Smoke will emit from the exhaust as the engine burns away the remaining oil residue.
  • Stop the mower and check the dipstick. Top up the oil if necessary using the measuring jug.
  • Cut the lawn!

Conclusion – Re-Oiled and Ready to Mow

If you’ve overfilled oil in your lawn mower, don’t beat yourself up – it’s a common mistake! And, the remedy needn’t cost much more than the price of a new can of oil.

Irrespective of what type of mower you own, having the right tools for the job and following our step-by-step oil overfill fix will get your mower back into the field. Pronto!

In the meantime, let us know if you have more questions about what to do if you put too much oil in the lawnmower.

We have tons of experience tinkering with lawn mowers, tractors, engines, and small farmyard equipment.

And we’re always happy to help troubleshoot.

Too Much Oil In the Lawnmower References, Guides, and Works Cited:


Dan is our qualified diesel fitter and automotive mechanic. He’s been fixing machinery for over 30 years and has a real passion for the old stuff. he loves reviving things that others have given up on. He’ll fix anything with a cable tie and fencing wire and has had his hands on everything from log skidders, trucks, agricultural implements, tractors, and huge mining gear to outboard motors. He’s plagued by OCD. but that makes him a helluva mechanic! View all posts

Paul writes for a living, about trucks mostly. He lives away from the city and off the road, nurturing his love for all things outdoors –- like tiny house construction, country cooking, bushcraft, woodwork and power tools, alternative energy, and minimalist living. If there’s a way to Do It Yourself, Paul wants to hear about it, and try it out. Then he’ll write about it, and share his story with blog readers around the world. Paul was raised on a South African homestead where he tended two horses, a Jersey cow, and half a mile of split pole fencing. At age 16, he bought a dirt bike, pirated a punk rock compilation, and commenced a blind-rise adventure that continues to this day where words, Wabi-Sabi, cooking, all-terrain tires, and all things to do with canvas and wood are his fodder. His overarching existential question is – “What more does a man need than a cast iron pot and a pair of loose-fitting trousers?” View all posts

Lawn Mower and Tractor Insight

Humphreys Outdoor Power give you insight to make your tractor or lawn mower last with best practices to get the most out of your machine.

He Tried To Mess With A Royal Guard & Big Mistake

Signs its Time to Retire Your Lawn Mower

It’s the beginning of the mowing season, you’ve mown your yard a few times and you’ve seen how you’re mower is acting after a long winter. Now you have the hard decision of deciding whether or not its time to retire you’re faithful cutting machine or see if you can fix it up (or have us fix it up). We can’t speak to the sentimental bond between a man and his lawn mower but we can talk about economics and whether a lawn mower is worth being repaired. Here are five things that typically spell the end of the line for your mower. These repairs are usually more costly than the machine is worth. Of course there are exceptions to every rule, but in general here some signs its time to scrap your lawn mower.

You hear a knocking sound

If your engine is knockin’ you better be shoppin’- most of the time knocking in the engine is a result of a bent crankshaft or a broken or bent rod. This is a terribly expensive lawn mower repair and most of the time you’re better off looking for a new mower. One of the main causes of this is running the machine out of oil. Make sure you’re always checking your oil level!

Your Engine is vibrating too much

How much is too much? You’ll know. When it seems like the engine might vibrate right off your machine, you’ve got an issue. This is yet another sign of a bent crankshaft or broken/bent rod. Double check your oil!

Smoke is coming out of your exhaust

In some cases this can be repaired by a head gasket which isn’t usually that expensive, but in other cases your rings may be worn out causing your engine to use too much gas and scoring your cylinder. This can be caused by not cleaning your air filter (debris gets in the cylinder and wears down your rings), or your rings could just be worn out. Regardless, depending on the severity of the scoring it might be time for another engine and at that point you should be looking at a new lawn mower.

You’re using too much oil

This usually goes with smoke coming out of the exhaust. The oil has to go somewhere and it’s usually into the cylinder. If you have to add oil after each mow job, you’re either mowing way to much or you have a problem. Not to mention oil is in itself expensive.

This is one thing on this list that is external on the machine. If you have a rusty deck you’ve lost most of your support and you’re running the risk of the blades flying off while you’re mowing, among other things. In some cases the mowing deck can be the most expensive part of the lawn mower, so it sometimes means it’s time to find a new lawn mower.

Bonus Section: Fixable Issues (But you need to get your lawn mower repaired now)

Won’t Start: This seems pretty basic and can be caused by a lot of different things. One of the most costly is that you’ve lost compression. This means the fuel you’re running wont ignite. A lot of times this can be fixed with a head gasket or new set of valves

Losing Horsepower in heavy grass: This is another sign that you’re losing compression. Not only is it annoying, it can be a serious problem and its important to get it fixed soon.

Your engine is missing: This is most often caused by fouled plugs due to above average oil use. It can be caused by damaged rings, bad air filter or scored cylinder among other things. It can also be caused by debris in your gas tank which is a pretty easy fix. The moral of the story is that this can cause a serious problem down the road and you need to have a professional take a look at it immediately.

Don’t want your lawn mower die just yet? Avoid these common maintenance mistakes!

This article is intended for use with riding lawn mowers. Push mowers and handheld power equipment is different because minor repairs can quickly add up to the cost of a new unit. Riding lawn mowers and zero turn lawn mowers can be a little more tricky when it comes to deciding to replace them, simply because they’re a larger investment. If you’re experiencing one or more of these side effects with your mower contact us today.

Identifying Lawn Mower Noise – Popping, Grinding, Clicking…

Is you’re lawn mower making a strange noise? Want to know what it is or if you should be worried? You’re in the right place.

This article covers several of the most common lawn mower noise types and suggests how to fix them.

When listening for lawn mower noises, be attentive to any unusual sounds like grinding or rattling, which could suggest a need to balance mower blades. Balanced blades are vital for a quieter and smoother mowing operation.

Another very common sound a lawn mower can make is a popping sound coming from the engine. This noise can be alarming, but it’s usually an indication that your lawn mower is backfiring.

When you hear a popping sound coming from your mower it’s important to identify the root of the problem immediately.

Another common noise is rattling or banging. This often indicates that parts have worked themselves loose over time or were not tightened properly in the first place.

Common, but strange, mower noises

In this section, we will discuss some common noises that you might hear from your lawn mower and what they might mean.

Rod Knock

Have a listen to what rod knock sounds like:

Rod knock sounds like metal parts hitting each other forcefully inside the engine. In 25 years of repairing mowers I find that this sound is never good news.

You can confirm rod knock by looking for metal shavings in the oil. As the parts continue hitting each other the damage leads to metal breaking off the parts (best case scenario), or to catastrophic engine failure.

Don’t ignore a mower engine that sounds like it’s being hit with a hammer, it needs immediate attention by a small engine mechanic.

Lawn mower squeaks

If you hear a high-pitched squeaking noise coming from your lawn mower, it could be due to a loose belt or a worn-out pulley.

You can check the belt tension and pulleys by turning off the engine and removing the spark plug wire. Then, use a wrench to check the tightness of the belt and pulleys.

If you find any loose parts, tighten them up or replace them as necessary.

Lawn mower grinding noises

A grinding noise coming from your lawn mower could be due to a damaged blade or a worn-out bearing causing mower vibrations.

You can check the blade by turning off the engine and removing the spark plug wire. Then, use a socket wrench to remove the blade and inspect it for any damage.

If the blade is damaged, replace it with a new one. If the bearing is worn out, you will need to replace it as well.

Lawn mower rattling

A rattling noise coming from your lawn mower could be due to a loose or damaged part.

You can check for loose parts by turning off the engine and removing the spark plug wire.

Then, use a wrench to check the tightness of all the bolts and nuts on your lawn mower.

If you find any loose parts, tighten them up or replace them as necessary.

Causes of strange lawn mower noises

When you hear strange noises coming from your lawn mower, it’s important to identify the cause of the problem quickly.

Here are some common causes of noises in lawn mowers:

Loose Parts

A common cause of noise in lawn mowers is loose parts. If you hear rattling or clunking sounds, it could be due to loose bolts, nuts, or screws.

These parts can become loose over time due to vibration and normal wear and tear.

Check the engine, blade, and other parts to ensure they are securely fastened.

Worn Out Parts

Another common cause of noise in lawn mowers is worn-out parts. If you hear a grinding or squealing sound, it could be due to worn-out bearings, belts, or pulleys.

These parts can wear out over time and need to be replaced to ensure your lawn mower operates smoothly.

Dirty or Clogged Parts

Dirty or clogged parts can also cause noise in lawn mowers.

If you hear a choking or sputtering sound, it could be due to a dirty air filter or a partially clogged carburetor.

These parts can become clogged with dirt, dust, or debris, which can affect the performance of your lawn mower.

Clean the carb or replace the air filter to keep your lawn mower running smoothly.

Lawnmower Makes Loud Clanking Sound? (Possible Causes Fixes)

Lawnmowers can run into many problems, and they are often easy to identify based on uncommon sounds. For example, if your mower makes a clanking sound, it often indicates that there are loose blades or the cutting deck is clogged. Whether it be a problem with the cutting deck or oil, let’s explore why your lawnmower is making a clanking sound.

When using a gas lawnmower, you become accustomed to the loud revving the engine makes. However, what happens if you notice a sound that isn’t supposed to be there? In some cases, you might hear a loud, clanking sound while mowing. If you do, it could indicate one of a few different problems.

The most common reasons why lawnmowers make a loud clanking sound include loose blades, old engine oil, or a clogged cutting deck. To fix the problem, you may have to tighten your blades, change the oil, or clean out your deck.

Because there are multiple culprits for this noise, we’ll break down each option and its solution so that you can get your mower back up and running in no time.

Top Reasons Why Your Lawnmower Makes a Loud Clanking Sound

The Problem: A Loose Blade

Your lawnmower blades take a lot of abuse. Not only are they spinning at such high RPMs all the time, but if they knock against anything besides grass (i.e., tree roots, rocks, etc.), they can get dull and damaged relatively easily.

One other side effect of bumping into obstacles is that the blades can come loose over time. When that happens, you’ll hear some knocking or scraping as the piece begins to wobble. Over time, this problem will only worsen until they can shear the bolt holding them in place.

The Solution: Tighten the Blade

Fortunately, this fix is quick and easy, so you should be able to do it and continue mowing right after. If you’re using a push mower, all you have to do is lift it up to access the blades. You can learn more about how to do that here.

Once the mower is up, a single bolt and nut are holding the blades in place. Tighten the nut, and you shouldn’t have the problem anymore. If it doesn’t feel like the bolt is tightening, you might have to replace it. However, that is rare.

If you are using a riding lawnmower, you will have to either drive your machine on blocks to access the cutting deck’s underside, or you can use a jungle jack to raise the whole thing high enough to access the underside. Before working on the blades, be sure to disconnect the spark plug and raise the deck height all the way. A single bolt also holds the blades on a riding mower, so all you have to do is tighten it.

The Problem: Old Engine Oil

Much like your car, oil is critical for your lawnmower’s engine. Without it, the various components would scrape and rub against each other, causing them to overheat and potentially break. Ideally, you should change your engine oil at the beginning of each season, but if it’s been awhile, you could be using old oil.

When old oil is in the system, it can create a knocking sound within the motor itself. Because the fluid isn’t lubricating as well as it should, the piston doesn’t flow as smoothly as it should, which results in a knocking or clanking noise.

The Solution: Change the Oil

Fortunately, most automotive oil should work well in a small engine. We recommend SAE-5W 30, if possible. The W stands for “winter,” and the number before it refers to the oil’s viscosity in freezing temperatures. The higher the number, the better the oil works in cold weather. Unless you’re cutting your grass during the winter, 5W should suffice, but you can always use 10W instead if you’re worried.

Follow these steps to change the oil in a push lawnmower:

  • Step One: Run the Machine – Doing this warms the oil so that it flows out easier.
  • Step Two: Cover the Gas Cap – You can use a sandwich bag or some other plastic to insulate the gas cap. Doing this ensures that no fuel leaks out.
  • Step Three: Tilt the Mower – Make sure that the gas tank is facing up. Place an oil drip pan underneath the oil tank opening to catch the fluid. Wait for it to stop flowing out.
  • Step Four: Add New Oil – Tilt the mower back and start pouring oil into the tank. Most push mowers need about 14 ounces, but it differs between models. Refer to your owner’s manual before starting. If you put too much oil in the system, you will have to drain the excess. Use the dipstick to tell when you’re at the right amount.

If you are using a riding lawnmower, follow these steps to change the oil.

  • Step One: Run the Mower
  • Step Two: Locate the Drain Valve – This piece may be on the right or left side. Refer to your owner’s manual if you can’t find it. You will likely have to open the hood to access it.
  • Step Three: Place a Drip Pan and Towel – Some oil will likely drip out once you open the valve, so you want to be ready with a towel.
  • Step Four: Open the Valve – On some models, there is a valve and a stopper. If you only have the valve, attach the hose first (see next step).
  • Step Five: Attach a Drain Hose – Because of the valve’s location, the oil will drip over your lawnmower if you didn’t use a hose. You can buy an official drain hose from the manufacturer, or you can make one yourself. Just make sure that it fits over the valve and that you have some way of keeping it in place (unless you want to hold it manually the whole time). One way to allow the oil to flow faster is to open the dipstick while draining.
  • Step Six: Close the Valve – Once the oil is drained, you can close the valve and the stopper (if applicable). Remove the drain hose.
  • Step Seven: Add New Oil – Riding lawnmowers require about a gallon of oil, but again, refer to your owner’s manual for a precise amount.

Bonus: Change the Oil Filter

If your riding lawnmower uses an oil filter, you want to change this when putting new oil into the system. You will need a strap wrench to dislodge the filter and be sure to place a drip pan or towel underneath when removing it, as some oil will dribble out.

When placing the new filter onto the engine, we recommend rubbing a little bit of oil on the o-ring. Doing this will create a tighter seal. Put the new filter on before adding more oil so that any dirty oil from the old filter won’t contaminate the new fluid.

After installing this piece, be sure to run the mower for a few minutes so that oil can flow through the filter.

The Problem: Clogged Cutting Deck

When was the last time you cleaned your mower’s cutting deck? If you’re like most owners, it has likely been a couple of seasons or more. Grass, dirt, and other debris will collect on the deck’s underside, which can bump against the blades as they spin.

Cleaning your deck is always recommended, even if you don’t notice any clunking noises. Grass clippings are full of water, which can cause the metal to rust over time. If you don’t clean the deck, you will have to replace your mower sooner rather than later.

The Solution: Clean Your Cutting Deck

If you have a push lawnmower, you can either tilt the machine on its side or lift it from the front. We always recommend the latter option because tilting the mower can potentially cause fluids to leak out into the engine. If that happens, you could be looking at some expensive repairs.

Depending on how dirty your deck is, you should be able to get most of the debris out with a hose and a scraping tool. In extreme cases, you might have to scrub the deck with sandpaper or something rough to get it clean. Be sure to dry everything thoroughly afterward so that it doesn’t rust.

If you are using a riding lawnmower, it should have a wash port on the deck’s top side. Simply attach a hose with a special coupling, and that will work wonders. Be sure to put the deck at its lowest setting before starting.

The Problem: A Bent Crankshaft

The crankshaft is the most central piece of your engine, as it is what spins the blades and the drive belt. Usually, the crankshaft gets bent if you hit something large with the mower. Once it’s bent, you’ll notice both shaking and loud noises.

The Solution: Replace the Crankshaft

Unfortunately, replacing a crankshaft is expensive, so it might be cheaper to buy a new machine altogether. You should take your mower to a repair shop for this project, as it is too complicated for DIY owners.

Related Questions

My mower is making a rattling noise; what does that mean?

Generally speaking, any rattling noise means that some parts are coming loose. You will want to inspect the various pieces of your mower and tighten any loose nuts, bolts, or fasteners.

If my lawnmower still works with the clanking sound, do I have to fix it?

Yes, you should. The problem will only get worse, which means that it will be more expensive. The sooner you can fix your machine, the better.

We are a team of passionate homeowners, home improvement pros, and DIY enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and more with other homeowners! Whether you’re looking for a step-by-step guide on fixing an appliance or the cost of installing a fence, we’ve here to help.

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Riding Mower Won’t Start Just Clicks – Mechanics advice with pics

This is a problem that usually arises in the spring, and for most, the fix is really simple. You’ve come to the right place, and you’ll be cutting grass shortly.

So what’s the problem with a riding mower that won’t start just clicks. The most common reason for a clicking sound on a riding mower when you turn the key is a flat battery. Other possible reasons include:

Yes, it’s a long list, but you won’t have to check all of them; I’ll bet your problem is one of the first three; I have listed the likely causes in order of commonality.

If your mower won’t crank and makes no click sound – Check out “Lawn Tractor Won’t Start.”

Bad Battery Connections

Bad battery connections are very common, and by bad, I mean the power is not passing from the battery to the cables because the battery connections are loose, dirty, or damaged.

Loose Connections

Battery cables become loose because lawn tractors vibrate a lot; this is why it’s a good idea to service your mower at the start of every season, no matter how well she runs.

Dirty Connections

Dirty connections are usually caused by the weeping of battery acid at the battery poles. The acid then crystallizes, causing high resistance; it looks like a white chalky build-up on the connectors.

Cleaning Connections

To clean the connections, add a couple of spoons of baking soda and a small amount of water, and pour this onto the acid build-up on the connections and battery poles.

The soda neutralizes and removes the acid; you’ll need gloves and protective eyewear. After removing the acid, go ahead and remove the connectors and give them a good cleaning with a wire brush or sandpaper.

If you have some petroleum jelly, a small coat will prevent a future build-up.

2020 PowerSmart self propelled mower rod knock.

Connector – Mower blades and engines cause a lot of vibration; bolts come loose from time to time.

Check that both connections, positive (RED ) and negative (BLACK – ), are clean and tight.

Cables – Check the cables for damage, and corrosion; mice find them irresistible.

Flat / Faulty Battery

A flat battery is a real pain in the ass. I know what it’s like; you just want to cut the grass, right? The fastest way to solve this problem is to jump-start the mower.

Leaking Battery – Check your battery for leaks before attempting to jump-start. If it leaks and it’s a sealed battery, replace it.

However, it’s usually only wet batteries that leak, so best to check your electrolyte level and top up if necessary. As you know, the acid will burn the skin and eyes, so, you know, gloves, etc.

If the acid build-up is excessive, your battery may be on its last legs, so don’t be surprised if it fails or does so soon.

But if the leaking is excessive, don’t jump-start; replace it. Batteries are easy to fit; just be sure the battery is the correct size, and the poles are in the proper places.

Jump Starting

You’ll need jump leads and any 12-volt vehicle. Most cars, trucks, and even Hybrids have a regular 12-volt battery fitted somewhere. Sometimes finding it is the hardest part. If you’re unsure of the voltage, when you find the battery, a sticker on the casing will indicate 12v.

Of course, your battery might be faulty, jump-starting will probably get you rolling, but the problem will still be there. You can test using a voltmeter test tool, which I’ve listed here on the “Small engine repair tools” page.

To jump-start – begin by connecting the positive red of the mower to the red of the car.Now connect the negative black (-) on the car to a ground (GRD) source on the mower. (Any bare metal will work)

Connect – If you are not familiar with jump-starting, you’ll find a complete guide here, “Jump starting riding mower.” Add the cables in sequence 1, 2, 3, and 4, start the mower, and while idling, remove jumper cables in reverse order 4, 3, 2, and 1.

Battery Testing

You can check the battery and alternator using a voltmeter. Batteries don’t like sitting idle; they were designed to be charged and discharged continuously. A battery that gets fully discharged will sometimes not come back to life.

Use a voltmeter to check the battery voltage, and connect red to positive and black to negative. I have listed a voltmeter on the “Small engine repair tools page.”

Test – Check battery voltage using a voltmeter – attach a voltmeter to the battery and set it to 20 volts.

If you have a reading above 12.5 volts – go ahead and attempt to start the mower; watch the voltage; a reading below 8 volts is a bad battery and needs to be replaced.

Buying a Battery

When buying batteries – wet batteries will not ship with acid. The acid must be purchased, and the battery must be filled and charged; it’s a lot of work.

I would buy a gel or maintenance-free sealed battery; these can be shipped, fully charged, and ready to roll. Check out quality common ride-on mower batteries on the Amazon link below.

Battery Charging

You’ll need a battery charger to keep your battery in top condition over winter. I recommend a trickle/Smart charger; they’re simple to use; pop on the color-coded crocodile clips, plug it in, and that’s it. Forget it till next spring, then turn the key and mow.

I’ve listed a good-quality Smart charger on the “Small engine repair tools” page that won’t break the bank.

Batteries work best and last longer when their state of charge is maintained; off-season charging is always advised. Check out “Mower winter storage video.”

Charge – Always disconnect the battery before charging. Simply connect red to red, black to black, and plug in the charger. The length of time on charge will depend on how low the battery is and the amp rating of the charger. Usually, 2-3 hours cooking time.

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Faulty Solenoid

The solenoid is a large relay of sorts. When you turn the key to start your mower, a 12-volt supply from the ignition switch to the solenoid activates it. The solenoid’s job is to connect the battery to the starter motor and crank over the engine for as long as you hold the key.

The click sound is the solenoid trying to work by pulling in the armature; they fail regularly, and I replace lots of them.

However, the click sound can also be made for a few other less common reasons, and without fully diagnosing, you may find replacing the solenoid doesn’t solve the problem.

Hey, if you feel lucky and don’t want to do the diagnosing part, I understand. So, if your battery is full and the cables are tight, go ahead and replace the starter solenoid. They’re cheap and easy to fit.

Check out, “Mower solenoid repair tools” it lists useful tools and parts that will help you nail the repair.

Solenoid – Solenoids are a universal fit; they give lots of trouble.

On the upside, they’re easy to fit and cheap to buy.

Where’s the Solenoid?

Often just finding the starter solenoid can be challenging; I sometimes think that they hide them for fun. If you don’t find it under the hood, try under the rear wheel, behind the gas tank, or under the seat.

The easiest way – follow the red battery cable from the battery. On some engines, the starter and solenoid will be one unit (Kawasaki and Honda engines).

Where? – Husqvarna, craftsman-like to, hide theirs under the rear wheel fender or the dash beside the steering column.

However, most solenoids will be easy to locate. Fitting is easy, but do disconnect the mower battery first.

Solenoid Test

Remove – The first step in testing the solenoid – remove the spark plug.

If, when removing the spark plug, gas pours from the spark plug hole – move on and check “Carburetor troubleshooting.”

Test – Turn the key; if the clicking sound persists – Go ahead and replace the solenoid.

If, on the other hand, the engine cranks over, move on and check for excessive valve lash.

Tight – Check the solenoid terminals; all wiring should be secure and free from corrosion.

Binding Starter Motor

The gear head of the starter motor can bind against the flywheel; this locks the engine and starter motor together. So when you hit the key, all you hear is the click sound.


Testing for this condition involves turning the engine by hand anti-clockwise. Some engines will have a cover over the flywheel; if so, try turning the crankshaft with a ratchet and socket from the underside of the engine.

If turning the motor anti-clockwise frees it up – you have found your problem, the starter motor is binding. Usually, a spray of wd40 on the starter gearhead will fix it. If you are lucky, you can get the straw of the WD40 directed at the gearhead without removing any covers.

Starters can bind for other reasons – worn bearings, worn gear head, misaligned or loose starter motor.

Binding – Starters can bind against the flywheel. To fix it – spray the starter gear with wd40 and retest. If it continues to bind, replace the gear head or complete the starter motor.

Turning the engine anti-clockwise by hand will unlock it.

Excessive Valve Lash

Engines have valves that open and close in sequence. The inlet valve allows the fuel/air mixture in. It then closes and seals the combustion chamber. After the power stroke, the exhaust valve opens and allows spent gases out.

What’s Excessive Lash?

The valve lash describes a precise gap between the valve tip and the rocker arm. As the engine wears, this gap gets bigger and must be adjusted. The inlet and exhaust valve lash will usually be different specs.

Correct Lash

When the valve lash is set correctly – you crank over the engine, the valves open, and release cylinder pressure. This allows the engine to crank over at sufficient speed to create a spark strong enough to start up the engine.

When the valve lash is out of spec, the valve is late opening which means pressure in the cylinder is too great for the starter to overcome; that’s when you hear the click sound.

Incorrect Lash

Check out “Valve lash adjusting” it’s for a walk-behind mower, but the process is identical. Adjusting lash isn’t difficult but will require an inexpensive tool called a feeler gauge. You’ll find a link to a good feeler gauge set on the “Small engine repair tools” page.

Test – If you can, place your hands on the flywheel screen – try turning the engine clockwise.

If you’re unable, you likely have excessive valve lash. Lash should be checked every season.

Lash – Adjusting valve lash requires an inexpensive tool called a feeler gauge.


A carburetor fuel supply usually consists of a fuel bowl, float, and needle. The float is, as its name suggests, a float. Attached to it, is a needle with a rubber tip.

The function of the float is to lift the needle as the fuel level rises in the fuel bowl. When the fuel bowl is full, the needle will be pushed against the fuel feed port, sealing it.

Hydro-locking – Worn carburetor float needle seals have a habit of leaking gas into the cylinder, and when the cylinder is full of gas, the piston can’t move; this is known as hydro-locking. Because the piston can’t move, the engine will often make a clicking sound as you try to start the engine.

Removing the spark plug and turning over the engine will release the gas, but the carburetor float valve and the engine oil will need to be replaced.

Other signs that your carburetor needle seal leaks are: overfull oil level; white smoke from the muffler; oil leaking from the muffler; gas dripping from the carburetor; a strong smell of gas in the garage.

Fuel Valve Solenoid

Newer model carburetors have a fuel solenoid fitted to the bottom of the fuel bowl; its function is to stop the fuel supply when you shut the engine off. So if you have this newer type of carburetor fitted, you will not likely have a hydro-locking condition.

Leaking Carburetor Valve Seal

Failure commonly occurs in the older type carburetor when the rubber needle seal wears. This results in fuel filling the carburetor and eventually entering the cylinder and crankcase.

Gas in the Oil

If you have gas in the oil, don’t run the engine; the diluted oil offers little protection to internal components. First, fix the issue by replacing the carburetor and then changing the oil.

Check out “Carburetor types” page; it lists popular mower carburetors. Check out “Carburetor troubleshooting” also for more details on the issue.

Check Oil – Too much oil is a sign that your carburetor needle seal is leaking unless, of course, you overfilled the oil yourself.

Needle – The needle wears over time; they turn pink when worn. The fix – replace the seal or the complete carburetor. Using your manual fuel valve will prevent future problems.

Faulty Ignition Switch

A faulty ignition switch can cause all kinds of problems; the click sound can be caused by a bad connection in or at the back of the switch.

Try the Wiggle Test

When turning the key, wiggle the wiring at the back of the ignition switch and see if it makes a difference. It will very often show you where the fault is. Wiring pinouts are specific to each manufacturer.

Wiggle – Try wiggling the wires at the back of the ignition switch while attempting to start the engine; you may need a helper.

Often wires come loose but do check them for corrosion.

Faulty Control Module

Control Modules are not fitted to all mowers. The function of the control module is to receive a start request from the ignition switch and to output a 12-volt supply to the starter solenoid, but only if all safety sensors are in the correct position.

Control Module Test

Control modules do fail and also suffer from loose connectors. Try the wiggle test on the connectors and check for obvious signs of water/corrosion damage. The control module will often live behind the dashboard in a plastic box about the size of a mobile phone.

Wiggle – Like the ignition switch; wires come loose, have a helper attempt to start the engine while you wiggle the wiring connectors.

Check also for damage, water, or scorch marks on the panel itself.

Faulty Starter Motor

A faulty starter can fail electrically, mechanically, or both. Electrically – the copper winding can break; brushes can break or wear out. Mechanically – the top and bottom bearings and the gear head can wear. These issues can cause the starter to bind, so all you hear is the click sound.

Testing the Starter

Checking the starter motor is easy; connect a 12-volt supply direct from the mower battery to the supply wire at the starter. An even easier way is to cross the starter solenoid as per the guide below.

If you find your starter has failed, removing and fitting a new one is simple. The starter motor for Briggs and Stratton offers a good quality starter. Be mindful that BS has two types of starter – plastic gear head or metal; check before ordering.

Starter – Some starters will have a solenoid and starter motor combined in one unit.

To test, use a jumper lead to bring power from the positive of the battery to the positive post of the starter. If the engine doesn’t crank – Replace the starter.

Common – Most mowers will have the starter and solenoid separate.

Solenoids are fitted to the body, usually under the hood.

Test – Cross a metal screwdriver from one connection to the other, as per the picture.

There will be arcing (sparking) as the screwdriver contacts the poles.

RISK OF FIRE – Keep clear of gasCAUTION THE ENGINE MAY TURN OVER – Place the mower in the park with the parking brake applied and the blade off.

If the engine doesn’t crank over – your starter is faulty; replace it.

Internal Engine Damage

If you’re still reading, I fear the worst has happened. It’s unusual for mower engines to fail completely. They’re generally well-built robust units. I have seen failures like the con rod breaking out through the engine casing; the main bearing seizing; the con rod bending; cylinder head failures.

Some of these faults can be repaired, but most are uneconomic to repair.

New Engine

On the upside, if you have a total failure, a complete engine fully built with a guarantee is available, and fitting involves four bolts, two electrical connectors, a fuel line, a throttle cable, and a crank pulley.

BS and Kohler’s engines are of great quality and ready to go. The completed job will take less than two hours. Be mindful that all engines are shipped without oil.

Failure – Total failure doesn’t happen often.A hard life, and low/poor quality oil, without doubt, increase the chances.

Related Questions

Can you jump-start a mower? A flat or bad battery is a more common fault than a starter. Try jump-starting; if your mower starts, the battery needs attention. If jump starting doesn’t work, investigate a faulty solenoid or starter.

Can a bad alternator ruin a battery? A bad alternator can ruin a battery. Alternators have two main components. A voltage regulator that monitors and controls battery charging and the alternator whose job it is to create voltage. Common problems include a faulty regulator, which damages the battery, and alternator diode failure, which drains the battery.