By far the most common reason for the clicking sound is a flat battery, followed by loose battery connections, and the next most common reason - failed starter solenoid.

If your mower won't crank and makes no click sound - Check out "Lawn Tractor Won't Start".

Other possible but less likely causes, include: over full oil level; wrong oil type; internal engine damage; flywheel obstruction; crankshaft obstruction.

Yes, it's a long list, but you won't have to check all of these, I'll bet your problem is one of the first three on the causes list below.

Jump to Guide.

01. Bad Battery Connection

02. Flat/Faulty Battery

03. Faulty Solenoid

04. Binding Starter Motor

05. Excessive Valve Lash

06. Hydro-locked Engine

07. Faulty Ignition Switch

08. Faulty Control Module

09. Faulty Starter

10. Engine Seized

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.

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.

Are usually caused by a 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.

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

The soda neutralizes and removes the acid, you'll need gloves and protective eye wear. 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.

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.

It's usually only wet batteries that leak, so best to check your electrolyte level and top up if necessary. As you know 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 has failed or does so soon. Batteries are easy to fit, just be sure the battery is the correct size and the poles are in the proper places.

You'll need jump leads and any 12 volt vehicle. Most cars, trucks and even Hybrids have a regular 12 volt battery fitted, 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 just be faulty, jump starting will probably get you rolling but the problem will still be there.

When buying batteries - wet batteries will not ship with acid. Acid will need to be purchased and the battery will need to be filled and then charged, it's a lot of work. So I would buy a gel battery or a maintenance free sealed battery, these can be shipped and are fully charged and ready to roll.

You can check the battery and alternator using a volt meter. 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.

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

Batteries work best and last longer when their state of charge is maintained, off season charging is always advised. Check out "Battery Charging".

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 solenoids 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 your feeling lucky and you 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. 

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 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).

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 is a matter of turning the engine by hand anti-clockwise. Some engines will have a cover over the flywheel, if so, try turning the crankshaft with ratchet and socket, from the underside of the engine. 

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

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

• Engines have valves which open and close in sequence. The inlet valve allows 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. 
•  

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

• When 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, in order to create a spark strong enough to start up the engine.

When 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. 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. 

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.

When the cylinder is full of gas, the piston can't move, this is known as hydro-locking. Removing the spark plug and turning over the engine will release the gas.

Other signs that your carburetor needle leaks, are: over full oil level; white smoke from the muffler; oil leaking from the muffler; gas leaking from carburetor; strong smell of gas in the garage.

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 carburetor fitted, it's not likely you will have a hydro-locking condition. 

Failure commonly occurs in the older type carburetor when the rubber needle seal wears. This results in fuel continuing to fill the carburetor and eventually making its way into the cylinder and crankcase. 

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 change the oil. Check out "Carburetor troubleshooting".

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.

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 pin outs are specific to each manufacturer.

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 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 dash board in a plastic box about the size of a mobile phone.

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

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. Starter motor for Briggs and Stratton offer a good quality starter. Be mindful that B&S have two types of starter - plastic gear head or metal, check before ordering.

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: con rod breaking out through the engine casing; main bearing seizing; con rod bending; cylinder head failures. Some of these faults can be repaired but most are uneconomic to repair.

On the upside, if you have total failure, a complete engine fully built with guarantee are available and fitting involves 4 bolts, 2 electrical connectors, fuel line, throttle cable and crank pulley.

B&S engines are a great quality unit, ready to go. Completed job will take less than two hours. Be mindful all engines are shipped without oil.