The electric starter of an internal combustion engine consists of several elements that ensure the smooth operation of the entire assembly. Bendix is one of them. Without it, the engine cannot be started. This part is distinguished by the simplicity of the device and the principle of operation. As a rule, they are non-separable. A defective bendix must be replaced. From this material you will learn: what is a starter bendix and why is it needed, who invented it, how it works, works, breaks down, is repaired. Additionally, it is described how to distinguish between malfunctions of the overrunning clutch and the retractor relay.

What is a starter bendix?

Bendix is a part of a car's electric starter. Structurally, it is an overrunning clutch or a freewheel. This is a mechanism that transmits torque until the rotating part begins to rotate faster than the rotating one. When this happens, the bendix allows the driving and driven parts to rotate independently of each other. It works due to centrifugal force.

Bendix - general view
Bendix - general view
Bendix - front view
Bendix - front view
Bendix - rear view
Bendix - rear view

What is Bendix for?

Bendix in a car electric starter performs the following functions:

  1. At the moment the engine starts, it connects the starter armature to the engine flywheel.
  2. Provides reliable engagement of the starter drive gear with the flywheel ring gear.
  3. It softens shock loads that occur due to the sharp movement of the drive gear to the flywheel ring gear.
  4. Before starting the engine, it transmits the torque generated by the starter to the flywheel.
  5. After starting the engine, as long as the driver holds the key in the "start" position, allows the flywheel and starter to rotate independently of each other.

The bendix design is needed to perform the last function. All other tasks could be solved at the expense of a simpler node. The problem is that the starter rotates relatively slowly, while the running engine rotates much faster. If, after starting the engine, it is not immediately disconnected from the starter, the latter will be subjected to severe overloads and may fail. The driver usually holds the key in the "start" position for some time after starting, and only then releases it. It is at this moment that the overrunning clutch is activated, protecting the starter from overload.

Who invented the electric starter bendix?

Some car starters do not have an overrunning clutch. The transmission of torque is controlled by the driver, for which there is a button in the floor of the cabin. However, most production cars have a Bendix. It was invented and patented in 1910 by the American inventor and industrialist Vincent Hugo Bendix. Since then, the design of the bendix has not undergone drastic changes. As, however, and all other components of the electric starter.

Before the invention of the bendix... Electric starter and bendix are almost the same age. Before their invention, starting an automobile engine was carried out manually using a "crooked starter". It was an extremely uncomfortable, physically difficult and traumatic operation. When the engine started, and the driver did not have time to pull the handle out of the flywheel, he got it on his hands and other parts of the body.

Byron Carter (founder of Cartercar) died as a result of an unsuccessful crank start. Worried about this event, Henry Leland (the head of Cadillac) decided to come up with an automatic electrical device for convenient and safe starting of the engine. But he didn't succeed. In 1911, the electric starter, the concept of which has not changed dramatically until now, was invented by Charles Cattering.

"Crooked Starter"
"Crooked Starter"

The device and principle of operation of the bendix

To understand why the bendix does not turn the flywheel, you need to get acquainted with the device and the principle of operation of this mechanism.

In the classic version, this electric starter component consists of the following parts:

  1. Driven cage with gear.
  2. Leading clip with worm gear.
  3. Rollers with clamping springs.
  4. Buffer spring.
  5. Clip for the drive lever.

Bendix is located either on the gearbox shaft, or directly on the starter anchor, and moves along it due to the worm gear. The longitudinal movement of the mechanism is limited on both sides by retaining rings. To move the bendix along the shaft, a lever is used, which is actuated by a retractor.

Bendix device
Bendix device

Bendix algorithm:

  1. When the ignition key is turned to the "start" position, power is supplied from the battery through the signal wire to the retractor.
  2. The retracting winding of the solenoid is activated.
  3. The armature of the solenoid moves by acting on the lever and moving the bendix towards the teeth of the flywheel.
  4. The starter is introduced into reliable engagement with the flywheel.
  5. At the same moment, a power contact closes inside the solenoid relay, and power is supplied from the battery to the starter motor.
  6. The retracting winding is de-energized, the holding winding is activated.
  7. The starter rotates, turning the flywheel.
  8. The engine starts.
  9. The flywheel rotates faster than the starter rotates.
  10. There is a centrifugal force that moves the rollers in the bendix.
  11. The starter and engine continue to rotate independently of each other.
  12. The driver releases the ignition key.
  13. The contacts inside the solenoid open, power is no longer supplied to the starter, it stops.
  14. At the same time, the holding winding of the solenoid relay is de-energized.
  15. The solenoid and bendix return to their original position due to the force of the spring.
Bendix with starter off
Bendix with starter off
Bendix with starter on
Bendix with starter on

The use of centrifugal force in the overrunning clutch is possible due to its internal structure. While the rotation speed is low, the rollers are pressed by springs and rest against the toothed protrusions. When the driven cage begins to spin with a rapidly rotating flywheel of a running engine, centrifugal force acts on the rollers. It exceeds the force generated by the springs. Each roller moves to the wider area of its groove. As a result, the driven and driving clips of the bendix begin to rotate independently of each other.

Symptoms of a malfunctioning starter bendix

There are two ways to determine a Bendix malfunction - by the sound during engine start, and after disassembling the starter.

Consider how the starter behaves with a faulty bendix. The most typical failure of this part is when the overrunning clutch does not transmit torque from the starter to the flywheel. The leading clip rotates, and the knowledge stands still. In such cases, they say that the bendix does not turn the flywheel.

The sound of a faulty bendix is of two types. If the freewheel mechanism has recently broken down, then when trying to start the engine, a loud metallic ringing and grinding is heard. This is the noise of the rollers inside the bendix, which cannot rest against the worn out protrusions.

When the bendix brakes completely, the characteristic metallic sound is not heard. The starter rotates at maximum speed, but the flywheel is in place. This sound is easily distinguished from that which is heard during normal engine start.

How to check the starter bendix?

To make sure that the bendix is faulty, it is necessary to remove the starter from the engine and partially disassemble it. Next, you need to take one hand on the clutch cage, and the other on the gear, which engages with the flywheel. If the bendix is broken, then the gear will turn easily in both directions. On a serviceable part, it rotates easily in one direction, while it is impossible to turn it in the opposite direction with any effort.

A faulty bendix is not always possible to scroll in both directions by hand. Sometimes you need to use tools
A faulty bendix is not always possible to scroll in both directions by hand. Sometimes you need to use tools

Other reasons for the inoperability of the bendix

Wear on the lugs that the rollers rest against is not the only possible reason why the bendix does not turn the flywheel.

The reason may also be the following:

  1. Flywheel teeth damaged. The absence of even one tooth on the flywheel ring makes it impossible to start the engine. To determine this breakdown, immediately after dismantling the starter, look at the flywheel. The damaged place should be in a visible place, since it was in this place that the bendix could not turn the flywheel. If, after an unsuccessful start by the starter, the car started up from a tow, the defective area may be in an inaccessible place. To check the flywheel crown, remove the spark plugs (or diesel injectors), crank the crankshaft by hand while inspecting the flywheel crown.
  2. Damaged bendix gear, which should rotate the flywheel. Damage is determined by visual inspection.
  3. Damaged worm gear. To see the malfunction, you need to remove the bendix from the shaft.
  4. The clip to which the lever is attached is broken. Usually it is made of plastic and is a ring with two protrusions. Located at the back of the bendix.
  5. Broken lever. It is also made of plastic, although it breaks quite rarely. Damage is determined by visual inspection.

In the first case, the flywheel ring needs to be replaced. In all other cases, the bendix must be replaced. This item is not repairable.

How to determine what is not working - a retractor relay or a bendix?

When the engine fails to start with the starter, it may not be the bendix that is to blame, but the solenoid. How to determine that it is the bendix that is not working, and not the retractor relay? Very simple. To do this, you need to understand how the starter works, in general.

Car starter diagram
Car starter diagram

In the event of a solenoid failure, the following does not occur:

  1. The bendix does not move towards the flywheel.
  2. The starter motor is not receiving power.

As a result, when the key is turned to the "start" position, two variants of events are possible - either clicks are heard, but the starter does not rotate, or nothing is heard at all.

If the starter spins, but does not turn the engine, then only the bendix is to blame. In the event of malfunctions of the retractor relay, as a rule, power is not supplied to the starter, and it does not rotate.

Detailed material on checking the starter solenoid relay is on the website.

Typical causes of a bendix malfunction

Despite the fact that the overrunning clutch is a non-repairable part, it will be useful to know about its breakdowns.

These include:

  1. Critical gear wear or damage.
  2. Reducing the diameter of the rollers.
  3. Availability of flat working on the rollers.
  4. Worn or broken protrusions against which the rollers about.
  5. Broken springs.

Quite rarely, the cause of a Bendix failure is its jamming due to dirt and rust. The force of the solenoid is not enough to move the freewheel to the flywheel. This problem is fixed by cleaning and lubricating the assembly.

How much does it cost to change the starter bendix?

Replacing the bendix is a relatively inexpensive procedure. The price of the part varies in the range of 5...20 dollars. The replacement service at the service station costs about the same. You can save half of these costs if you replace the faulty bendix yourself. Although this procedure is not easy, as it requires some tools and the right actions.

Do-it-yourself starter bendix repair

It is impossible to restore a damaged bendix. For repair, the part is changed entirely according to the following algorithm:

  1. Disconnect one terminal from the battery.
  2. Disconnect the power and signal wires from the solenoid relay.
  3. Remove the bolts that secure the starter to the engine.
  4. Remove the solenoid relay by first disconnecting the power wire going to the starter.
  5. Loosen the bolts that hold the parts of the starter housing together.
  6. Disconnect the bendix drive lever.
  7. To remove the bendix from the shaft, remove the retaining ring.
  8. Put a new bendix on the shaft.
  9. Reinstall retaining ring.
  10. Assemble the starter, install it on the engine and connect the wires.
Remove the solenoid
Remove the solenoid
Loosen the starter housing bolts.
Loosen the starter housing bolts.
Disconnecting body parts
Disconnecting body parts
The same retaining ring with a clip
The same retaining ring with a clip

The most difficult thing in this procedure is to remove and install the retaining ring, which limits the movement of the bendix towards the flywheel. On many starters, it has a tricky design and consists of a ring and a clip. To remove it, you must first knock down the clip, and then remove the ring. Assembly is carried out in the reverse order.

Other starter articles:

The starter clicks, but does not turn: 10 malfunctions and repairs

Starter takes over: symptoms and underlying causes

10 reasons why the starter turns bad