Repairing threads
Fixing thread damage cleanly
The problem Thread damage
Damaged threads must be precisely restored. With suitable repair solutions, full functionality can be reliably recovered.
Damaged threads are part of everyday workshop life: over-torqued bolts, stripped threads in aluminum components, broken studs. Often, the only option seems to be a complete replacement of the component – at considerable cost.
But in many cases, a damaged thread can be professionally repaired. With the right tools and thread inserts, this is faster and cheaper than a replacement.
- Stripped thread pitches (too much torque)
- Pulled-out threads in aluminum (cylinder head, engine block)
- Broken screws and studs
- Corroded threads (rust, salt)
- Worn threads from frequent loosening/tightening
Risks without repair
A damaged thread means:
Bolt no longer holds (component comes loose), torque cannot be applied, sealing is no longer guaranteed (oil or coolant leaks), complete replacement of the component (cylinder head, engine block, etc.) = very expensive.
Repairing a thread is almost always cheaper than replacing the entire component.
Thread inserts & repair kits
Professional thread repair follows proven principles:
Drilling out: The damaged thread is drilled out to a larger diameter. Cutting a new thread: A new (larger) thread is cut with a special tap. Installing the thread insert: A Helicoil or Time-Sert insert is screwed in. This has the original thread on the inside. Function restored: The bolt can be tightened again with full torque.
Especially with aluminum components (cylinder heads, transmissions, engine blocks), thread inserts are often the only economical solution. They restore full load capacity and are permanently durable.
Application areas
Typical use cases:
Spark plug threads in aluminum heads, glow plug threads, oil drain plug threads (frequently over-torqued), sensor mounting (lambda sensor, temperature sensor), suspension components (control arms, wheel bearings).
With the right technique and the right tool, even critical threads can be repaired while still installed. This saves removing large assemblies and significantly reduces repair time.
Frequently asked questions
What thread repair systems are available (HELICOIL, TIME-SERT)?
The two most common systems are HELICOIL (stainless steel wire thread inserts) and TIME-SERT (solid steel sleeves). HELICOIL inserts are flexible, easy to install and available for many thread types. TIME-SERT sleeves offer higher strength due to their solid construction and are particularly suited for high-load applications such as cylinder head bolts.
When should a thread be repaired and when should the component be replaced?
Thread repair is worthwhile when the carrier component (e.g. cylinder head, engine block) is intact and only the thread is damaged. If there are cracks in the carrier material or structural damage, component replacement is the safer choice. In most workshop cases, a damaged thread can be fully repaired with a HELICOIL or TIME-SERT insert.
What thread sizes do the PICHLER repair sets cover?
PICHLER offers thread repair sets for all common metric thread sizes from M5 to M18, including fine-pitch variants such as M8x1, M10x1.25 and M12x1.25. Special sets for glow plug threads (M8x1, M9x1, M10x1) are also available. The sets come fully equipped with drill bits, taps, installation mandrels and matching inserts.
What is the difference between HELICOIL and Ensat inserts?
HELICOIL inserts consist of a coiled stainless steel wire and are screwed into a re-drilled thread — they provide a flexible, vibration-dampening connection. Ensat inserts, on the other hand, are made of brass or steel and are anchored by cutting their own external thread as they are screwed in, without requiring an additional tap. Both systems are standards-compliant and permanently load-bearing.
Can I also repair light-alloy (aluminium) threads?
Yes, thread repair in aluminium components is one of the most common applications. HELICOIL and TIME-SERT inserts made of stainless steel or steel create a durable, corrosion-resistant thread in aluminium. During installation, ensure the correct bore diameter and clean thread cutting, as aluminium is soft and easily damaged.
What tools do I need for threads in glow plug bores?
For glow plug bores you need a drill-out set for the appropriate glow plug thread (M8, M9 or M10) plus a matching thread repair set. PICHLER offers combination sets that allow drilling out, cleaning and thread repair in a single workflow. A centring adapter ensures precise alignment and prevents misalignment during drilling.