When looking for the reason your blades aren’t spinning you’ll have to check out the mower deck components, clutch, switches, and items powering the clutch.
SCAG mower blades won’t engage or turn on when the deck belt is worn, the tensioner arm and spring are worn, the PTO switch is faulty, the clutch is bad, the battery is weak, the safety switch is faulty, or the fuse is blown.
Follow all safety precautions before working on your mower. This includes removing the ignition key and spark plug wires. Wait for all parts to stop moving.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
SCAG Mower Blades Won’t Turn On or Engage
Worn Deck Belt
Check the condition of the mower belt. The belt is responsible for gripping the deck pulleys to turn the mower blades. When the deck belt is worn, the belt may slip on the pulleys and the blades won’t turn.
A worn or bad deck belt is one that has cracks, fraying, or a shiny glazed appearance. A worn deck belt may also sit deep in the pulley grooves.
Replace a worn belt. Even if the blades do rotate, they may spin at reduced speeds. This will affect the cut quality.
A fast blade speed is required to create suction under the deck to lift the grass and give it a nice even cut.
Belt Came Off the Pulleys on the Mower Deck
If you find the belt has fallen off the pulleys and will no longer turn the mower blades, you’ll need to look at the condition of the belt and items that can cause the belt to fall off like a bad pulley, worn tensioner arm, or missing spring.
You can find a list of items that will cause the SCAG belt to keep falling off the mower deck here.
Worn Idler Tensioner Arm & Spring
A tensioner arm and spring are used to hold the idler pulleys inline. You will most like find a pulley on one side of the bracket and a spring on the other side.
These pieces can wear over time causing the belt to vibrate off the pulleys. The spring can break or stretch. The hole in the bracket can also wear causing affecting the tensioner.
Worn Idler Pulley Bearing
You will find bearings in the pulleys on the mower deck. The pulley can wear over time. This may cause the pulley to no longer sit securely parallel to the mower deck.
Instead, a bad bearing may cause the pulley to wobble. The belt can roll off of a pulley when there is a rocking movement to the pulley.
To find a bad pulley, slowly rotate the pulley by hand and feel for resistance or listen for a bearing noise indicating the pulley is going bad. Grab each side of the pulley and see if there is extra play allowing the pulley to rock back and forth.
A good pulley will sit securely on the deck. Replace a pulley assembly where the bearing is found to be bad.
Faulty PTO Switch
The PTO switch is usually a knob installed on the mower that allows voltage from the battery to power the clutch. When the switch fails, the blades won’t turn on.
Check for continuity in the switch. Replace a switch with a break in continuity.
The PTO (Power Take Off) clutch transfers power from the engine to the blades by engaging the drive belt. A clutch that is worn or faulty must be replaced when it fails to power the blades.
For more details on clutches, check out A Look into How Lawn Mower Clutches Work.
The battery is used to power the clutch solenoid to engage the mower blades. The clutch won’t get enough power when the battery is weak.
Check the voltage of the battery using a multimeter. A fully charged 12-volt battery should give you a reading of about 12.7 volts. Charge the battery when you get a reading less than this.
If your battery continues to die you can find common things that are causing this in 5 Things That Are Draining the Life of Your Lawn Mower Battery.
Charge a Battery: Use a battery charger to charge your battery. Before you continue, wear protective gear to protect your skin from electrical shock and protect your eyes.
Follow these steps to charge your riding mower or zero-turn battery with a charger:
- Access the battery and terminals. You may need to use a screwdriver to uncover the battery. You will find the battery under the hood or under the seat. Do not remove the battery from the casing.
- Connect the battery charger cables beginning with the positive cable first. This is the red cable or the one with the plus sign. Place the cable on the positive battery terminal.
- Attach the negative cable to the negative battery terminal. This is the black cable or the one with the negative sign.
- Do not touch anything that doesn’t have a rubber coating to prevent electrocution.
- Set the charger’s voltage and amperage level to the desired level. The average volt level for lawn mower batteries is usually 12 volts. More amperage charges the battery faster. Start with two amps and work up to no more than 10 amps. A slow charge is best.
If you find the battery won’t hold a charge, you must replace it with a new one. You can find 12-volt lawn mower batteries at your local hardware or automotive store. You may also find batteries at your local SCAG mower dealership.
Bring the old battery with you. Most places will charge you a core fee unless you provide them with your old battery. Stores typically charge $15-$25 for a core fee.
Bad Safety Switch
A SCAG uses a safety switch in the seat as part of its operator presence system. The seat switch is installed under the seat to sense when the mower operator is in the seat.
As part of the safety system, the lawn mower blades won’t turn on without the operator in the seat.
If the seat switch fails to work, it may not properly sense the operator. The safety system will prevent the blades from engaging with a bad seat switch.
Test the seat switch using a multimeter or you can temporarily bypass the safety switch to identify a bad switch. Do not operate a mower without the safety switch installed for your safety.
Always have safety switches installed and working on your equipment.
When you aren’t getting power from the battery to the clutch, you may have a blown fuse. The fuse is used to protect the zero-turn electrical system.
Replace a blown fuse with the same size fuse. If you continue to blow fuses, I recommend taking your mower to a SCAG service dealership or a lawn mower repair shop to find the root cause of the electrical failure.
Still Experiencing Problems with Your SCAG Lawn Mower?
Own a lawn mower long enough, you’ll start running into problems with it starting, not continuing to run, smoking, leaking gas, giving a bad cut, vibrating, or another issue.
To help you save time and money, I have put together a guide to help you troubleshoot the next problem that develops on your mower.
You can find this guide at Common SCAG Lawn Mower Problems & Solutions.
If you are unsure how to perform diagnostics and repairs on your lawn mower safely, it’s best to have a professional complete the repairs.
This will help you avoid personal injury or additional damage to the mower. Your local SCAG lawn mower dealership or lawn mower repair shop will be able to help you solve your problem.