Spark Plug Thread Repair
Damaged spark plug threads often come from over-tightening. A thread repair kit lets you cut new threads without removing the cylinder head. Choose the correct thread size, often M14 x 1.25. Check the available depth in the plug hole to select the right insert length. The tap cleans the old thread, and the insert provides a new, strong thread. This ensures the spark plug torques correctly and prevents future failures.
Tap | M16 x 1.25 | for BGS 149
Threaded Sleeves | 11 mm | M14 x 1.25 | 5 pcs.
3 pack sizes
1-2
Thread Inserts | M10 x 1.0 | for BGS 165 | 4 pcs.
Thread Inserts | M12 x 1.25 | for BGS 166 | 4 pcs.
Thread Inserts | M14 x 1.25 | for BGS 150 | 4 pcs.
Thread Inserts | M8 x 1.0 | for BGS 167 | 4 pcs.
Repair Kit for Spark Plug Threads | M14 x 1.25 mm | 5 pcs.
Repair Kit for Spark Plug Threads | M8 x 1.0 | 5 pcs.
3 pack sizes · from €27.48
1-2
Spark Plug Socket Puller | for VAG / Mercedes-Benz | 320 mm
Internal Spark Plug Rethreader | M12 x 1.25 mm
2 pack sizes
1-2
Spark Plug Thread Cleaner with Seal Seat Cutter | M14 x 1.25
Repair Kit for Spark Plug Threads | M14 x 1.25 mm | 16 pcs.
Repair Spark Plug Threads Yourself
Which size do you need?
Spark plug thread repair starts with the right size. The most common is M14 x 1.25. Smaller engines often use M12 or M10. Always check the old spark plug or the cylinder head number. This ensures you order the correct tap and thread inserts.
Measure the space and length
Measure the available space in the spark plug well. A straight set only works if you have good access. For angled or deep wells, choose a set with an extension. Thread inserts come in different lengths, from 11 to 19 millimetres. Measure the thickness of the cylinder head to select the right insert. An insert that is too short does not grip enough. One that is too long protrudes and can damage the spark plug.
Where ordering goes wrong
Many mechanics only order the tap and forget the thread inserts. A repair kit contains both parts. Make sure the thread inserts are made of hardened steel. This prevents them from turning when you tighten the spark plug. Always use a torque wrench when fitting the spark plug. This prevents the thread from being damaged again.
This tool belongs with Engine & Attachments. If you work on spark plugs more often, also look at Spark Plug Tools for wrenches and at Glow Plug Thread Repair for diesel engines. For seized parts you sometimes need Other Special Tools.