Starter Spins But Does Not Engage

When you turn the key or press your car’s start button, a boost of electricity is sent to a small starter motor and its solenoid. Its cogged teeth provide a vigorous short-term boost to get the engine cycling as sparks meet a fuel/air mixture to initiate the magic of internal combustion.

Though what happens if the starter motor is spinning normally but not engaging the engine? The engine itself won’t get the boost it needs to engage the Bendix with the flywheel to start the internal combustion cycle.

If the starter motor is spinning but failing to crank the engine, this could be due to various factors, including a low car battery strength, a failing or bad starter solenoid, or a failed or damaged Bendix drive gear that fails to catch the flywheel.

When the starter motor fails to engage the car engine, you’ll be left stranded where you’re parked.

So, finding the reason why your starter spins but does not engage starts with taking a closer look at how a starter motor works. Then we can troubleshoot what might be hampering the car’s ability to turn over completely, and what, if anything, you can do to fix it.

How Does a Starter Motor Work?

Your car’s starter motor is the first mechanical step in initiating the internal combustion process. When you turn the ignition key or press the vehicle’s start button, it engages an electromagnetic solenoid inside the starter motor.

At that point, a rod with an attached pinion is pushed out and engages the engine’s flywheel. As the starter motor turns it physically cycles the engine over, this helps to draw in air to fix with the fuel delivered by the fuel injectors to create the necessary fuel/air mixture to support internal combustion.

Once the necessary spark is delivered to fire the cylinders, the engine maintains the internal combustion cycle on its own, and the starter disengages.

The starter motor’s pinion and the solenoid go through much use and abuse throughout years of firing up a car’s engine. This can be compounded by other mechanical faults like bad spark plugs or fuel system issues, which lead to hard starting or frequent stalls and restarts. However, there are certainly other things that can affect starter performance.

Where is Starter Motor Located?

Where is Starter Motor Located?

Most automakers put the starter on the driver’s side, usually down low near the transmission and the lower part of the engine block. Though some rear-wheel drive cars are made with the starter on the passenger side of the lower engine block.

The starter looks like a big cylinder with a smaller cylinder riding piggyback on it. If you can’t immediately find it by looking, you should check the owner’s manual or the repair guide.

What Causes a Starter Motor to Spin and Not Engage?

The most common reasons why your starter spins but won’t engage include electrical system problems a failure in the Bendix or a fouled solenoid. To ferret out which one is at the root of the starter motor problem, we’ll have to take a closer look at what each component does.

Top reasons why your starter spins but doesn’t engage

1. Low Battery

Low Battery

Low battery voltage is one of the most common reasons why a starter spins without without starting the vehicle. In a scenario like this, the battery isn’t completely flat, but the voltage is low, or the battery connections are corroded to the point that it can’t deliver the voltage the starter motor needs.

The low voltage condition essentially results in the Bendix gear being unable to engage the flywheel with enough vigor to initiate the internal combustion cycle.  

A low-voltage battery in this sorry state will also cause all kinds of other electrical or if you have a weak car battery, it can cause all sorts of electrical problems in the car, including the starter motor. This is because the battery powers all the electrical devices of your car.

If your starter motor is starter spinning but not engaging the flywheel, one of the first things you should check is the battery voltage. If it’s low, try charging the battery or jump-starting the car. If that doesn’t work, you may need to replace the starter motor. starter motor spins but does not engage the flywheel

How to Fix Low Battery Voltage

If you suspect it’s a battery problem or a faulty alternator, start by checking the battery for corrosion on the terminals and clean the terminals if necessary.

If the battery terminals look fine, then you’ll have to have the battery and/or the alternator tested to determine which needs to be replaced. Most auto parts stores will perform these tests for free.

2. A Failed Bendix Gear

A Failed Bendix Gear

A starter motor that spins without engaging the engine could be caused by a failed or damaged Bendix drive gear. Originally invented by Vincent Hugo Bendix a defective plunger, pinion gear, or ring gear can prevent the Bendix gear’s armature from rotating and engaging with the flywheel.

When you have a fault in a starter motor’s Bendix gear, you often hear a clicking or grinding noise coming from the starter motor. Sometimes only one or two of the gear teeth is broken. This causes the starter motor to engage sometimes and then spin fruitlessly.

How to Fix a Failed Bendix Gear

If any part of the Bendix drive gear is damaged, the starter motor itself will need to be replaced. This is a dynamic component with multiple parts that cannot be feasibly repaired for less than the cost of a complete starter motor replacement.

3. A Faulty Solenoid

A Faulty Solenoid

Several solenoid problems can cause your car’s starter to spinning over without engaging the engine. The starter’s solenoid is a large wire coil surrounding a solid iron core.

When you turn the key, electric current flows from the battery through the coil, which produces an electromagnetic field. At that point, the starter’s solenoid turns the motor’s armature as the Bendix gear engages the flywheel.

If the coil of the starter motor develops a fault or is burned out, it might not be able to deliver the current necessary to produce a strong electromagnetic field. This manifests at a starter that spins but does not engage.

It’s also possible for sticky solenoid contacts to cause the starter motor to spin without engaging the flywheel. In a situation like this, dirt, dust, rust or corrosion interfere with the gap in the electrical contacts within the starter’s solenoid. The gap is often less than one millimeter, so it doesn’t take much to get in the way.

How to Fix Sticky Solenoid Contacts

Spraying a little dry electrical contact cleaner on the solenoid, such as MAF cleaners spray, might be enough to remove dirt and grime from sticky solenoid contacts. If you’ve got some on hand, it’s worth trying before resorting to more expensive repair or starter replacement options.

How to Test for a Defective Solenoid Coil

If a defective solenoid coil is what’s causing the starter to spin fruitlessly, you will likely need to replace the starter motor completely. The simplest way to test if the starter solenoid coil is defective. Calls for a simple 12-volt test light and the following steps.

  • Step One: Disconnect the negative terminal from the car’s battery.
  • Step Two: Touch one end of the test light to the positive terminal on the solenoid
  • Step Three: Touch the other end of the test light to the small wire going to the starter motor.

If it doesn’t light up, the solenoid is most likely defective, and the starter should be replaced.

4. A Bad Fly Wheel

A Bad Fly Wheel

A damaged flywheel that doesn’t make good contact with the Bendix drive gear could also be the reason your starter spins without turning over the engine. The flywheel is basically a heavy metal disc attached to the end of the crankshaft. When the car’s engine is running, the flywheel rotates continuously to keep the engine rotating smoothly.

If the flywheel is damaged, the starter motor’s Bendix might not be able to engage properly. This will cause the starter to spin fruitlessly. This is usually a problem that develops in the long term if the starter’s Bendix essentially grinds on the gear connection of the flywheel.

How to Fix a Bad Fly Wheel

If the relationship with the starter motor is the only problem with the flywheel, a professional mechanic might be able to resurface it for around $350 to $500. A bad flywheel usually has other effects on the engine performance, and most mechanics will recommend a complete replacement.

The cost to replace a bad flywheel can range from $475 to $900 or more. Depending on what other mechanical problems the bad flywheel might have also caused.

5. A Starter Wiring Problem

A Starter Wiring Problem

A loose wire, damaged wiring harness, or even corroded wires and bad connections can prevent the starter from getting the necessary voltage it needs to spin the flywheel vigorously. You might be able to find this with a visual inspection. Especially if there was recently water or other fluids released in your engine bay. You might be able to see and clean the wiring connections.

How to Test Starter Motor Wiring

You can test with a multimeter and the following steps if it is a suspect wiring or connection problem.

  • Step One: Disconnect the car’s negative battery terminal.
  • Step Two: Set the multimeter to the continuity setting for voltage.
  • Step Three: Touch one of the leads to the positive terminal on the solenoid and the lead to the small wire that goes to the starter motor.

If the multimeter doesn’t read any continuity, the problem is likely in one of the wires on your starter motor. It will need to be repaired or replaced to get the starter motor to spin and engage.

Starter Motor Replacement Cost

Starter Motor Replacement Cost

The cost of a mechanic replacing a starter motor ranges from $150 to $400, with the real-world average landing around $300. Roughly half of this cost is the part, and half is the labor.

If you are a modestly capable DIY auto mechanic, you might be able to replace your own starter motor. This will take around three to four hours, so it’s a question of your mechanical skills as well as your time.

Frequently Asked Questions

What does it mean when the starter spins but doesn’t engage?

When the starter motor spins without turning over the engine, and you can rule out any low voltage or electrical fault, it usually means that there’s a problem with the Bendix drive gear. One or two teeth can fracture or degrade, causing the starter not to make sufficient contact with the flywheel to let it cycle the engine long enough to turn over.

How do you manually engage a starter?

Manually engaging a starter motor or “Jumping” the starter is possible if it’s merely an internal wiring fault affecting the solenoid. This involves touching a screwdriver with a rubber handle or a similar piece of conductive metal to the metal end of the post that leads to the starter. Then you need to touch the other connection for the wire that leads to the battery.

This essentially transforms the screwdriver into a manual switch that bypasses the solenoid. Once you make contact, you’ll need someone else to turn the key to start the engine immediately. Don’t be surprised if you see a lot of sparks. The instant the engine turns over, pull the screwdriver away to prevent heating and even accidentally arc welding the screwdriver to the starter.

Where to hit a starter to make it work?

You can sometimes hit the top part of a starter with a hammer to essentially knock some of the rust and/or corrosion off the internal brushes. This will hopefully get them moving again. However, it’s best to use a block of wood to make contact to prevent the head of the hammer from damaging the starter’s exterior housing.

Will a jump help a bad starter?

If your starter spins but does not engage due to a low battery voltage issue from a bad alternator or corroded battery terminals, a jump start from another car might help get the engine started. Though this is more about delivering sufficient electrical support to the starter motor.

If the reason the starter spins but doesn’t engage is linked to a more serious failure, such as bad wiring, a faulty Bendix drive gear, or a damaged flywheel, jump-starting the battery will have no effect.

Conclusion

Your starter spins but doesn’t start the car’s engine, usually due to mechanical failures in the Bendix drive gear, the flywheel, or a physical wiring problem. Though it’s also possible the reason the starter spins but doesn’t start is linked to an internal failure of the solenoid.

If the problem is related to electrical connections or battery problems, the important components of the starter might be just fine. You’ll need to either clean and reconnect the wires and/or fix the battery/alternator problem. This also holds true for a flywheel problem, though resurfacing or replacing a flywheel can be an expensive repair bill.


If the problem is a major internal fault in the Bendix gear or a failure in the solenoid, the starter likely needs to be replaced.

Jason Farrell

Written By

Jason Farrell

Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.

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