Replace a coil on a Craftsman riding lawn mower step by step

Craftsman riding lawnmowers are sturdy machines that a high cutting power and reliable. But also, with a reliable lawnmower, there can always be a problem. On a Saturday, the weather has cleared, a good time to start mowing your lawn. But your trusty Craftsman lawnmower won’t start as soon as you turn the key. The first thought is that the problem is either with the spark plug, the battery, or the ignition coil. Upon testing the battery and the spark plug, it becomes clear that both are working fine. This way, you have managed to narrow down the real culprit of the issue, the ignition coil.

How to replace a coil on a craftsman riding lawnmower, step by step:

• Step 1: Remove the ignition coil from the lawnmower. It is located inside the lawnmower engine attached to the flywheel magnet
• Step 2: Diagnose the ignition coil using a multimeter. Compare the resistance.
• Step 3: Buy a new ignition coil as recommended by Craftsman. Make sure the specification matches the old ignition coil.
• Step 4: Replace the old coil with the new
• Step 5: Test the lawnmower with the new ignition coil

The lawnmower’s ignition coil is located inside the lawnmower engine and is attached to the flywheel magnet. The starter coil’s service life may end due to corrosion of its metallic body or if the lawnmower has not been used for a long time. A lawnmower can have one or two ignition coils, depending on the lawn mower’s number of cylinders. However, the test procedure for the ignition coil is the same regardless of its number. Here are the measures that will help you inspect not only the ignition coil but also repair it.

Working on the lawnmower ignition system

The ignition system is the electro-mechanical mechanism that provides initial power to the machine to start. Each of these elements works together to start the engine. After starting, the starter motor and the flywheel do not have to do much work. However, the rest of the cycle goes on and keeps the engine going. In a craftsman lawnmower the ignition system, the following are the main items:

● Battery

It provides a source of electricity. It keeps the charge stored and gets charged through the alternator that runs from a belt transferring power from the crankshaft.

● Starter motor

The initial push allows the engine to perform first intake and compression. The starter system is separately installed and has a solenoid that will enable the power from the battery to the starter motor.  

● Flywheel

The transmission from the flywheel that is turned to move the piston in the cylinder as required

● Ignition coil

It acts as a transformer and steps up the 12 V from battery to high voltage for spark production

● Relay

Allows the current to flow with specific timing when the spark is required inside the cylinder during the power stroke

● Sparkplug

The component directly in contact with the combustion chamber generates a spark to burn a fuel-air mixture and produce power. It has a very special insulation coating on its rear end.

 How to replace a coil on a craftsman riding lawnmower:

•Step 1: Remove the ignition coil from the lawnmower

• Locate the ignition coil: The coil is generally present right next to the blower wheel on top of the engine. So, lift the hood and try to take an idea of what the location would be. First, you need to unscrew the nuts that hold the cover of the blower in place. Next, lift the lid off and place the nuts back on the studs so that the nuts and the spacers remain safe. A rectangular component is seen nearby of the flywheel. It is the ignition coil
• Remove the sparkplug cable: Find the sparkplug. It is usually present on the side of the engine block. Carefully pull the cable off. If the cable was not snuggly fit, then the wire will need a replacement too.
• Disconnect the kill wire: One wire is permanently attached to the coil leading up to the sparkplug. On the opposite side, another terminal is present. This is the kill wire terminal. Gently pull the clip off using a pair of grip pliers.
• Take the coil out: Unscrew the bolts holding the coil in place and smoothly take it out.

•Step 2: Diagnose the coil using a DMM

• Set the multimeter: Adjust the multimeter to the resistance setting. Check the multimeter by touching both the probes together.
• Check the manual for common values: Craftsman lawnmower coils have high resistance, so keep the setting in 20k ohms. In the instruction manual provided with the lawnmower, check the nominal values of resistances.  
• Check resistance from high tension terminal: Touch the red wire from the DMM to the metallic piece present in the sparkplug boot. The black terminal is connected to the base of the ignition coil. The resistance value should be compared with the value in the manual.
• Check the kill wire terminal’s resistance: Touch one terminal to the ground (a metal part of the lawnmower) and the other terminal to the coil base. Again, make a comparison to the manual’s value.

If any value obtained deviates by a significant number, the ignition coil needs to be replaced. 

•Step 3: Buy a new ignition coil as recommended by Craftsman

• Buy the same model as the old one: Whenever you buy any component, the best way is to take the older part with you to the shop. Look for the part with the same coding, specification, and preferably manufacturer too. The ignition coil’s replacement must be the same as the original coil that came with the mower.
• If part not available on the market, contact craftsman customer care: Sometimes, you can not source the coil locally. The part you are looking for was made by a manufacturer who discontinued the same production. In this case, contacting the lawnmower manufacturer, i.e., the Craftsman, is a better way.
• Check the manufacturer’s manual: Mostly, the Craftsman manual gives some more information about the part. So, if the exact or recommended part is not purchasable from the market, go for the best alternative.

•Step 4: Replace the old coil with the new

• Reinstall the sparkplug: Clean the head of the sparkplug. Check the gap and correct it when needed. First, tighten the spark plug in place with your hand to keep the threads and the insulation safe. Also, check the resistance and current leaks before reinstalling. Tighten the sparkplug using a spark plug socket wrench.
• Place the new coil back: Before installing the new coil, clean its area. Remove any corrosion or dirt from the flywheel. Use an all-purpose cleaner to clear the marks left behind by the old coil. Let it dry, put the coil in the correct location, and attach the bolts by hand. Do not tighten before adjusting the gap.
• Adjust the gap using feeler gauge: The gap that should be present between the flywheel magnets and the coil is mentioned in the manual. Turn the magnet side of the wheel towards the coil. The magnet will pull the coil and attach it to itself. Pull the coil away, place the indicated thickness feeler gauge in between, and let go of the coil. Tighten the bolt on one side. Remove the feeler gauge move the magnet to the next side, and repeat the procedure. In case you are getting confused, contact a professional.
• Tighten the bolts: use a torque wrench and apply enough force to tighten the bolts all the way. Please do not use a huge force because it will damage the threads permanently.  
• Fit the sparkplug cable: The wire attached on one side of the coil has thick insulation over it. It is a high-tension wire. On the other end of the wire, a grip is present. This is called the boot. Fix it on the jack of the sparkplug extending from the cylinder on the engine. Make sure the fit is proper. Try to place this wire away from the exhaust manifold.
• Reattach the ground/ kill wire: Using grip pliers, pull and attach the clip of the kill wire onto the coil’s other terminal.

•Step 5: Test the lawnmower with the new ignition coil

• Reassemble all the parts: Put the cover back in place. Tighten the nut to hold it tight in place. Check the volts on the battery and all-electric safeties and fuse. Lower the hood to close.
• Check the mower: Turn the ignition switch and start the lawnmower. If the lawnmower has started and is humming, the fix is done correctly!

Precautions

• Use Insulated tools: Use properly insulated metal tools like pliers, wrenches, and screwdrivers, etc.
• Safety gear: For some of the tasks, it is a good idea to wear some safety equipment, like goggles and insulation boots.
• Disconnect the battery: Remove the ground terminal of the battery do the circuit is incomplete during the procedure
• Clean connections: Clean all the electrical connection and clip before reattachment

Related questions:

1. What can be the reason if the ignition system is fine, but the mower still does not start?

The major culprit in such a case can be the starter solenoid. Try jumping the solenoid to start the lawnmower.

2. Can prolonged use of a weaker battery reduce the life of the ignition coil?

A weaker battery can cause no damage to any component. However, you should replace the battery as soon as it starts to feel a bit lousy.

Final Remarks

If your lawnmower doesn’t start, the ignition coil may be malfunctioning. But the lawnmower’s ignition coil can easily be removed, tested, and replaced if needed. Don’t forget to perform timely maintenance to other parts of your lawnmower’s like filters, cutting blades, and oil.