The starter Bendix drive is one of the most popular car starting mechanisms. Throughout the history of motor vehicles, the device has helped crank and start engines. Join us as we explore the Bendix starter in this guide. You will learn about how the drive works, its components, and a lot more. We also included plenty of Bendix starter images to make the guide easier to understand.

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What is Bendix Drive in a Car?

The starter Bendix drive is a type of drive used to transfer the rotation of the starter motor to the flywheel. You can easily find the device in your car by looking. It’s usually an assembly of a pinion drive gear on a splined shaft and mounted on the shaft of the starter motor.

The Bendix starter derives its name from Vincent Bendix, the person behind its invention. For a long time, the drive has been the standard mechanism for starting IC engines. It comes in two major designs; the inboard and outboard.

• Inboard- In the inboard design, the pinion moves inwards toward the starter motor. The construction provides a shorter shaft for the pinion than the outboard type, which makes it more efficient and robust. As a result, inboard drives are the most common.
• Outboard- The outboard drive features a pinion that slides outward, away from the starter motor. Its shaft usually longer than that of the inboard type. The length makes it less rigid due to the higher bending stress it experiences. These drive types are less used.

Starter Bendix Drive Function

A starter motor generates the force to start an IC engine. But the motor cannot achieve that without a helping system. This is where the Bendix starter drive comes in. The device helps to transmit starter motor rotations to the flywheel, thereby cranking up the engine.

After the engine has started, the Bendix drive disengages the pinion gear from its mesh with the flywheel. This ensures the engine’s rotation does not end up driving the starter motor and causing damage. In summary, the starter Bendix drive for electric starter systems performs these functions.

1. Transfers the turning force of the starter motor to the engine to help produce the first compression cycles.

2. Disconnects the starter drive gear from the flywheel once the engine starts and protects the motor from damage.

Versions of the Starter Bendix Drive

The starter Bendix drive exists as two different versions: the dated inertial pinion and the modern solenoid-operated drive. The two mechanisms mainly differ in their method of thrusting the pinion toward the flywheel, as explained below:

Inertial Pinion Bendix Drive

This drive type uses the principle of inertia to start the engine. Usually found in older model starters, the mechanism offers an automatic engagement and disengagement of the pinion gear.

Many cars still use the Bendix starter drive, despite it being a traditional technology. A lot of improvements have come up over the years, though, making the drive more effective. Advancements have led to inertial pinion drives that incorporate reduction gears and friction clutches.

The standard inertial Bendix drive consists of weighted pinion gear, a threaded sleeve, and springs. The pinion gear slides freely along the sleeve, with its forward movement helping it to reach and engage the flywheel. The springs help to control the pinion’s movements as well as absorb their shock.

Pre-engaged Starter Bendix Drive

The pre-engaged Bendix drive uses a solenoid to push and retract the pinion drive gear. The solenoid is usually fixed on the top of the starter motor, moving the pinion via a fork-shaped lever. The drive’s operation is thus electrically operated, compared to the automatic action of the inertial pinion type of drive.

The pre-engaged drive gets its name from the way it operates. Unlike the inertial type, its pinion engages the flywheel before the motor begins to rotate in full force. As a result, its operation produces far less wear of the pinion and flywheel gears. There is also less likelihood of severe damage such as the teeth of the gears breaking.

Pre-engaged Vs. Inertial Pinion Starter Bendix Drive

The inertial pinion Bendix drive has both good and bad sides. The solenoid type too. Here is a comparison of the two versions of the device.

The pre-engaged drive uses an electric actuator to move the pinion. That requires extra power (and drains the battery). Despite that, the mechanism offers a safer way to mesh the pinion and flywheel gears. The two components engage before the motor begins to rotate, making the operation less violent.

The pre-engaged Bendix starter drive is more reliable than the inertial pinion type. Every movement can be controlled, which offers a higher probability that it will work. These drives are more difficult to diagnose, though, since they contain electrical components.

Inertial pinion type of Bendix drives offer several benefits. Their operation is entirely mechanical, which makes them easy to maintain or troubleshoot. They are also less of a challenge to troubleshoot when faulty. When used with gear reduction mechanisms, these drive types use little power to start an engine.

The main disadvantage of the inertial pinion starter Bendix drive is the violent engagement that characterizes its operation. The pinion gear has to mesh with the flywheel long after the motor has powered. That subjects the teeth of both flywheel and pinion gears to excessive wear and damage.

The Bendix Drive Working Principle

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As we have seen, the Bendix starter drive comes in two types. These also work differently and use different components to cause engagement and disengagement. Because both starter drives are used in today’s cars, we will explain their operation separately.

Inertial Pinion Drive

This drive type uses a special type of mechanism to start an engine, offering the advantage of automatic engagement and disengagement. Generally, the device utilizes inertial force to thrust the pinion to the flywheel, and the flywheel’s back drive to unmesh it. The process can be divided into two phases; engagement and disengagement

Engagement

• Turning the ignition key powers up the starter motor. The armature rotates, causing the Bendix driveshaft to also spin. The weighted pinion gear does not rotate with the shaft immediately. Due to inertia and the fact that it’s loosely attached to the shaft, it lags behind. Instead, the gear slides forward along the threaded shaft
• As the pinion moves on the threaded shaft, a heavy duty spring connected to the starter motor shaft also winds up. When the pinion reaches the end of its travel, it encounters a restraining collar. The collar prevents the gear from moving further and locks it with the shaft. That results in the starter motor rotating the pinion gear.
• By now, the pinion is also in mesh with the flywheel’s ring gear. This causes it to rotate the flywheel and start the engine. The heavy spring on the drive’s head helps to absorb the shock of engagement. There is also usually a smaller spring at the end of the pinion’s travel that provides the same effect.

Disengagement

• As soon as the engine starts, the flywheel and the pinion gear cannot stay in mesh anymore. That’s because the engine causes the flywheel to rotate the pinion at high speed, higher than that of the starter motor. When that happens, the pinion gear is immediately thrown out of engagement.
• The unmeshed pinion gear quickly slides back on the threaded shaft to its former position. The retracting action of the pinion gear happens automatically, facilitated by the flywheel’s back drive. In most drives, the pinion winds up a light spring during its forward movement. The spring helps to slide the pinion back after the engine starts.
• The large and main Bendix starter drive spring helps to cushion the pinion from violently returning to its original position. It also aids to retract it from the flywheel. It’s important for the pinion gear to disengage from the flywheel when the engine starts. Doing so prevents the higher speed of the engine rotating the starter motor and causing damage.

Pre-engaged Drive

The pre-engaged Bendix drive relies on a solenoid to work, as earlier indicated. The solenoid moves the pinion to the flywheel’s gear and back again when the engine starts (or when you release the ignition key). The following is what happens.

Engagement

• When you press the button to start the engine or turn the ignition key, current first flows to the starter solenoid. A little current also flows to the motor to turn it slowly and allow the forward movement of the pinion.
• The starter solenoid coils energize, pulling a plunger and holding it for as long as current flows. The moving plunger pulls at a fork that acts as the lever to push the pinion gear towards the flywheel. The plunger also closes a circuit to provide full current to the starter motor.
• The motor rotates the starter Bendix drive shaft. By now, the pinion gear is already in mesh with the flywheels ring gear. This causes the motor to rotate the flywheel, starting the engine.

Disengagement

• Releasing the ignition key or button results in the current of the starting circuit cutting off. This de-energizes the starter solenoid coils, releasing the plunger. A heavy spring retracts the plunger, moving the fork and causing the pinion to unmesh with the flywheels gear. The retracting plunger also cuts the starter motor current, making it to stop spinning.

Starter Bendix diagram showing the different parts

Main Starter Bendix drive Parts and their Functions

The proper working of a starter Bendix drive assembly relies on its individual parts. The main components include:

Drive Pinion Gear

It’s the small gear on the drive’s sleeve or shaft. Its function is to transmit the motor rotation to the flywheel and start the engine. It does so by engaging the flywheel’s ring gear whenever a driver turns the ignition key. The gear only has a few teeth. This is to enable it to provide the large turning force required to rotate the flywheel.

Drive Shaft

The shaft is the part that holds the pinion gear. In a pre-engaged drive, the it contains straight grooves to lock it with the pinion gear. In the inertial type of Bendix starter drive, the shaft has helical grooves. These serve to guide the pinion as it slides toward the flywheel and back again when the engine starts..

Main Spring

This is the helical spring on the drive’s shaft. It winds when the starter motor powers and the pinion gear moves to engage the flywheel. The Bendix starter drive spring serves several functions. It allows the pinion gear to reach the ring gear of the flywheel. It also cushions the gear from the mechanical impact of the engagement.

Other Parts

Other essential parts that help the starter Bendix drive to function include:

• Shift Fork

The shift fork pushes and retracts the pinion gear in solenoid-operated Bendix drives. The fork attaches to the solenoid plunger on one side and the pinion gear on the other. It’s usually pivoted to allow free movement.

• Friction Clutch

Positioned between the drive’s shaft and the motor, the Bendix starter clutch helps to cushion against the shock of engagement and disengagement. It connects with the Bendix assembly when it moves to rotate the flywheel and disengages when the engine starts.

• Reduction Gears

When a Bendix drive comes with reduction gears, it means increased torque to crank the engine. A set of gears are arranged to decrease the output speed while increasing the rotational force. As a result, the drive can overcome larger loads to start a heavy duty engine.

Starter Bendix Drive Problems

The components of a starter Bendix drive assembly experience violent movements. That often causes rapid wear of the drive, sometimes even damage by breaking off parts. Some of the problems that you might encounter with the Bendix starter device in your car include.

• Worn pinion gear teeth- the teeth on the pinion gear wear off with time. Eventually, the wear reaches a point where it affects the drive’s performance. Results include the gear not engaging the flywheel and the engine not starting.
• Broken pinion gear teeth- this problem is usually caused by the rough engagement of the pinion and flywheel gears. It causes starting problems and requires immediate action.
• Damaged small components- the Bendix drive on a starter system contains components to ensure proper operation. If any of these breaks or becomes damaged in any way, the drive’s operation becomes impaired.
• Dirt in the threads- the pinion gear on the inertial Bendix drive moves along splines or grooves on the shaft. When these grooves accumulate dirt and debris, the movement is restricted. The result is the Bendix starter sticking in its path. With the starter Bendix stuck, the engine cannot start.
• Broken spring– the helical spring on the Bendix drive assembly helps to thrust back the pinion gear. If it breaks, problems such as the pinion gear not retracting start to show.

Starter Bendix drive problems can mean a car that cannot start. Some can be fixed while others call for replacing the entire assembly. Inertial pinion Bendix drives often fail due to dirt on their grooved shafts. Cleaning the shaft often restores their working. In the solenoid operated Bendix drives, failure often results from bad electrical connections in the solenoid.

Starter Bendix drive FAQs

So far, we have seen how the Bendix on a starter works, the parts involved, and problems that can occur over time. For more information about the device, here are common questions and their answers.

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Q1. Where is the Bendix starter drive located?

A. The Bendix drive helps transmit the energy of a spinning starter motor to the flywheel. As such, you can expect its location to be near both the motor and vehicle’s transmission. The device is usually found in the front part of the motor, keyed or attached to the motor’s shaft on one end.

The starter Bendix drive location allows for efficient engagement and disengagement of the pinion drive gear. It also makes it possible to use a small sized device, helping to increase performance and lowering costs. Here is a starter Bendix drive diagram showing the device’s location in relation to the starter motor and flywheel.

Q2. How do you tell if the Bendix drive is bad?

A. The Bendix drive helps to start the engine by turning the crankshaft. Therefore, its failure will show up as engine starting problems. Signs include the engine failing to crank, not starting, or grinding noise.

Some problems are not caused by the device itself. They may be external, such as a damaged solenoid that cannot operate the shift lever, a faulty starter motor, or a weak battery. It’s recommended to troubleshoot the battery first when you have starting problems.

Q3. What are the Reasons for the Bendix starter not engaging flywheel ring gear?

A. There are several causes. They include broken or worn teeth on the pinion and flywheel’s gear, teeth alignment issues, and a weak or damaged solenoid. It could also be a damaged motor. Because many problems could cause the issue, it’s advisable to troubleshoot the entire starting system.

Q4. What is the reason for starter Bendix not retracting?

A. The inertial pinion Bendix features a helical spring. The spring winds up before the pinion gear reaches the flywheel, building up enough energy to move the gear back. It can only do so if intact. A weak or broken spring causes the pinion to remain engaged. Other causes include teeth misalignments, bad spacing between the teeth of the gears, dirt, and other imperfections on the flywheel or the pinion.

Q5. Can you lubricate a Bendix drive shaft with engine oil?

A. It’s not advisable if you have an inertial pinion type of drive. Lubricating the shaft cause engagement problems. The resulting low friction prevents the weighted pinion from moving forward to mesh with the flywheel.

Q6. Can Bendix starter pinion damage the flywheel?

A. It rarely happens. Flywheel ring gears are made from a very hard material, harder than that of the pinion gear. In the event forceful engagement between the two components, it’s often the teeth of the pinion gear that get stripped. Most of the time, the pinion wears off, leaving those of the flywheel intact.

Q7. How do you fix starter Bendix drive problems?

A. There are two options. Changing the damaged components or replacing the drive. It depends on the type of damage or the part that has broken down. Replacement is usually the most recommended option. That is because most problems occur when the device has lasted its lifespan.

Q8. What is the Bendix drive price?

A. It depends on the type of Bendix starter drive, its design, quality, and brand. The application too, since different drives fit different motor vehicles. However, the Bendix drive is a fairly low-cost component. Prices range between $20 to $100.

Q9. What is the Starter Bendix replacement cost?

A. Bendix drive services do not cost much, especially if the drive in your vehicle is easy to access. The amount to pay ranges around $100. That’s with the exclusion of the cost to buy the drive. DIY projects are possible if replacing Bendix in starter systems of older vehicles. In news ones, it’s more recommended to look for a professional to do the job.

Conclusion

The Bendix on a starter system is a small device that performs useful functions. It’s also one of the most common, both in older model and newer cars. The drive offers little challenge to maintain, repair, or even change, with many car owners finding the tasks doable. When buying one, it’s advisable that you know what to expect from the drive type in terms of performance.

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