Drilling out & removing glow plugs
Workshop-grade solutions for broken glow plugs
The problem Broken glow plugs
Broken glow plugs must be precisely removed. Special tools help to center accurately, drill in a controlled manner, and protect threads.
Glow plugs in diesel engines are exposed to extreme thermal and mechanical stress. After many operating hours, they can seize in the thread or break off during removal attempts.
A broken glow plug in the cylinder head is a serious problem: The engine runs rough, metal shavings can enter the combustion chamber, and a conventional repair is hardly possible.
Risks
Incorrect drilling can make the problem worse:
Thread in the cylinder head is damaged or destroyed, shavings enter the combustion chamber (engine damage), drill bit breaks off (an even bigger problem), cylinder head must be removed (high effort).
Professional drill-out kits
Special glow plug drill-out kits are designed exactly for this situation:
Centering device: Ensures the drill bit starts exactly in the center. Stepped drill bits: Different diameters allow step-by-step drilling without overload. Thread protection: The surrounding thread is not damaged. Thread repair: After drilling out, the thread can be restored with inserts.
Each kit is designed for specific engine types and contains all necessary components.
Step-by-step procedure
The removal is carried out in controlled steps:
1. Centering: Position the centering device on the glow plug. 2. Pre-drilling: Start drilling the glow plug body with a small drill bit. 3. Drilling out: Gradually remove the glow plug body with larger drill bits. 4. Removing remnants: Extract glow plug remains with special tools. 5. Thread repair: Check the thread and repair with inserts if necessary.
With the right tools, this work is possible even without removing the cylinder head. This saves time, costs, and enables a quick repair.
Tools in action
See how our professional tools are used in the workshop.
Frequently asked questions
What to do when a glow plug has broken off?
When a glow plug breaks or its head shears off, the remaining body must be drilled out of the cylinder head. PICHLER offers specialised drilling-out kits that precisely remove the residual shaft without damaging the cylinder head. Afterwards, the thread is restored with a repair insert.
Which tool do I need to drill out a glow plug?
For drilling out you need a suitable glow-plug drilling kit with centre drill, step drill and thread tap. PICHLER offers both vehicle-specific and universal (UNI) kits covering M8, M9 and M10 threads. A sturdy drive, such as a cordless drill with torque clutch, is also required.
Which thread sizes are used for glow plugs (M8, M9, M10)?
The most common glow-plug threads in diesel passenger cars are M8x1, M9x1 and M10x1. M9x1 is frequently found in Ford, Peugeot/Citroën and PSA engines, while M8 and M10 are widespread among German manufacturers. PICHLER kits cover all three sizes in one set.
What is the difference between the BASIC and UNI drilling kit?
The BASIC kit is designed for one specific thread size and is ideal for workshops with a clearly defined vehicle range. The UNI kit covers all common glow-plug threads (M8, M9, M10) in one compact set and is suited for shops servicing multiple vehicle brands.
How do I avoid cylinder head damage when drilling out glow plugs?
Always work centred and at low speed to minimise material loss on the aluminium cylinder head. Use the supplied centring adapter to align the drill precisely with the remaining thread. Coolant or cutting oil reduces heat build-up and protects the material.
How does thread repair work after drilling out?
After drilling out, the damaged thread is re-cut with a tap and a repair insert (e.g. HELICOIL or TIME-SERT) is fitted. This fully restores the original thread size and strength. PICHLER offers matched repair sets that combine drilling out and thread restoration in one workflow.