The starter knocks when starting, but the car starts: causes and solution to the problem

Why the starter knocks, but the engine still starts: let’s look at the symptoms

You turn the key in the ignition, hear a characteristic metallic knock from under the hood - but the engine still starts. The sound may resemble hammering, clicking, or even grinding. Many drivers ignore this symptom, attributing it to the “features” of the car. However Starter knocking when starting - this is a direct signal of a malfunction, which over time can result in expensive repairs.

In 80% of cases, the problem lies in the mechanical part of the starter or parts associated with it. Less often the electrician is to blame. The main danger is that ignoring knocks leads to flywheel tooth wear, bendix failure or even jamming of the starter. In this article we will look at all possible causes of knocking when starting the engine, when the car still starts, and we will give clear instructions for diagnosing and troubleshooting.

1. Wear of the solenoid relay: why it clicks but does not work immediately

The most common cause of knocking is Solenoid relay malfunction. It is responsible for two key processes: extending the bendix (starter gear) and closing the contacts to supply current to the electric motor. When the relay is worn out, it the anchor does not lock in the extreme position, and the gear “bounces” several times as it hits the flywheel.

How does this manifest itself:

• 🔊 Single or multiple knocks when turning the key (sometimes accompanied by clicking sounds).
• 🔄 The engine can start in 2-3 attempts.
• ⚡ The backlight on the dashboard dims at the time of startup (a sign of a voltage drop).

You can check the solenoid relay without removing the starter:

1. Have an assistant turn the key to the start position.
2. Listen to sounds from under the hood: if you hear click → pause → knock → start, the relay is faulty.
3. Check the voltage on the relay control wire (should be 12 V when the ignition is turned on).

2. Bendix problems: when the gear “jumps” on the flywheel

Bendix (overrunning clutch) - This is the starter gear that meshes with the engine flywheel. If its teeth or spring mechanism are worn, the gear does not lock firmly and "slips" along the flywheel crown, creating a knock. This happens especially often on cars with mileage over 150,000 km.

Signs of a faulty bendix:

• 🔧 Grinding or crackling noise after successful launch (the gear has not disengaged).
• 🔄 The knocking sound is heard only when it is “hot” or “cold” - it depends on the temperature expansion of the parts.
• 🛠️ Visually: chips and burrs are visible on the teeth of the bendix or flywheel.

For diagnostics, the removed starter is checked on a bench or manually:

1. Turn the Bendix gear by hand: it should rotate one way only (in reverse - block).
2. Inspect the teeth: if they have the shape of “fangs” (and not even trapezoids), the part must be replaced.

What happens if you don't change the bendix?

Ignoring the problem leads to “licking” of the flywheel teeth. In critical cases, the starter stops clinging to the flywheel altogether, and the engine cannot be started without repairing the clutch basket (cost - from 15,000 rubles).

3. Damage to flywheel teeth: when the starter is not to blame

If the bendix is working properly, but the knocking noise persists during startup, the problem may lie in flywheel - a massive disk connected to the crankshaft. Its ring gear wears out from constant contact with the starter, especially if there were previously problems with the bendix.

How to recognize flywheel wear:

• 🔊 Knocking is heard only at startup, and not while the engine is running.
• 🔍 Upon visual inspection (removal of the gearbox is required), “bald spots” are visible on the teeth.
• 🚗 The problem is progressing: at first the knocking was rare, then it became constant.

The solution is to replace the flywheel crown or the entire flywheel (on some models, e.g. VW Golf IV or Toyota Corolla E120, the crown is removable). The cost of work is high (from 8 000 ₽), since it requires disassembling the transmission.

Reason for knocking	Character of sound	Repair cost (₽)	Difficulty in eliminating
Solenoid relay wear	Single click + knock	1 500–3 000	Low (relay replacement)
Faulty bendix	Repeated knocking or grinding noise	2 000–5 000	Medium (starter replacement)
Wear of flywheel teeth	Clunking sound on startup	8 000–20 000	High (removing gearbox)
Loose starter mount	Rattling + knocking	500–1 500	Low (bolt tightening)

4. Loose starter: when the bolts are to blame

A trivial but often overlooked reason - loose starter bolts. Due to vibrations, they spin up, and the starter housing begins to “walk”, and the Bendix gear hits the flywheel. This problem is common on cars that have been repaired (for example, after replacing the clutch) when the bolts were not tightened to the correct torque.

Signs:

• 🔧 Knock accompanied by rattling starter housing.
• 🔩 Visually: a gap is visible between the starter and clutch housing.
• 🛠️ The problem appears after off-road travel or long driving.

The solution is to tighten the fastening bolts (the tightening torque is usually 30–40 Nm). On some models (for example, Renault Logan or Kia Rio) access to the lower bolt is difficult - it may be necessary to remove the crankcase protection.

5. Electrical problems: low voltage or oxidized contacts

Less commonly, the starter knock is associated with electrical faults:

1. Low battery: When the voltage is low, the solenoid relay cannot hold the gear in mesh and it “jumps.”
2. Oxidized terminals: poor contact leads to current loss and unstable relay operation.
3. Starter brush wear: the electric motor rotates jerkily, which causes knocking.

Diagnostics:

• 🔋 Check the battery voltage with a multimeter: when starting it should not fall below 10.5 V.
• 🔌 Inspect the battery terminals and starter wires: oxides or melting are a sign of poor contact.
• 🔍 Remove the starter and check the length of the brushes (the minimum allowable is 7–8 mm).

Ring the circuit from the ignition switch to the solenoid relay|Measure the voltage at the battery terminals when starting|Clean the starter contacts and ground wire|Check the starter fuse (usually F10 or F20)

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6. Mechanical damage: when the starter “rests” on the flywheel

In rare cases, knocking is caused mechanical defects:

• 🔧 Clutch housing deformation (for example, after an accident), due to which the starter is at an angle.
• 🛠️ Entry of foreign objects between the starter and the flywheel (nuts, fragments of fasteners).
• 🔄 Starter bearing wear, because of which the shaft plays and the gear hits the flywheel.

Diagnosis requires removal of the starter and visual inspection. Please note:

1. Impact marks on the starter or flywheel housing.
2. Starter shaft play (permissible - no more than 0.5 mm).
3. Integrity of fastenings and absence of cracks.

What to do if the starter knocks: step-by-step algorithm

To avoid guessing from the coffee grounds, follow this plan:

1. Step 1. Diagnosis “by ear”: determine the nature of the knock (single, multiple, grinding).
2. Step 2. Check the fastening: tighten the starter bolts (torque 30–40 Nm).
3. Step 3: Solenoid Test: if you hear clicks without operation, the relay needs to be replaced.
4. Step 4. Inspection of the bendix and flywheel: If there is a grinding or cracking sound, disassembly is required.
5. Step 5. Electrical check: measure the voltage at the battery and starter contacts.

If the problem is not solved, remove the starter for detailed diagnostics. On most cars (eg VAZ 2110, Hyundai Solaris) you can do this yourself with a minimal set of tools: keys on 10, 13 and an extension cord.

FAQ: Frequently asked questions about starter knocking

Is it possible to drive if the starter knocks, but the car starts?

In the short term, yes, but it’s like playing Russian roulette. Each start increases the wear on the flywheel and bendix teeth. In the worst case scenario, the starter will jam and you won't be able to start the car without towing or replacing parts.

How much does it cost to repair a knocking starter?

The cost depends on the reason:

• 🔧 Replacing the solenoid relay: 1 500–3 000 ₽.
• 🔄 Starter repair (Bendix + brushes): 3 000–6 000 ₽.
• 🚗 Replacing the flywheel: 15 000–30 000 ₽ (with work).

Why does the starter knock only when it's hot?

This is a typical symptom thermal expansion details. When heating:

1. The teeth of the flywheel or bendix expand and “bite.”
2. Loose starter mounts have more play.
3. Worn starter bearings begin to “walk”.

The solution is diagnostics on hot engine (10-15 minutes after the trip).

Could the starter knocking noise be related to the transmission?

Yes, but indirectly. For example:

• 🔧 If you recently changed the clutch, you might have forgotten to install it flywheel support bearing.
• 🛠️ When replacing the gearbox, the flywheel may have shifted relative to the crankshaft.

In such cases, the knocking is accompanied by vibrations at idle.

How to temporarily eliminate starter knocking if there is no time for repairs?

⚠️ Attention: these measures are temporary and may worsen the problem!

1. Tighten the starter mounting bolts.
2. Clean the battery terminals and starter contacts from oxides.
3. Apply graphite lubricant to the Bendix gear (if there is access).

The maximum repair delay period is 1–2 weeks.