55. Thread Repair

Thread Repair

- Tools Required
- J 39345 Thread Repair Kit

The following procedure is used to accomplish proper and durable thread repairs in the cylinder head and the cylinder block.

Important: Take appropriate precautions to assure that machining chips will not remain inside the engine. For example, block all intake passages, oil drainback holes and exhaust passages with a towel or tape before performing thread repairs.

1. Select the proper size drill as indicated in the schematic charts found in Thread Repair Specifications for the hole being repaired.
2. Drill out the damaged threads to the original depth or completely through for through holes.

Caution: Refer to Safety Glasses Caution in Service Precautions.

3. Apply compressed air with a shop towel wrapped around the air spout, in order to retain the chips forced out of the hole.
4. Select the correct size tap, using the appropriate chart for the hole being repaired.
5. Coat the tap and the hole with spray machining oil.
6. Tap the hole to the original depth. In order to clean the threads, reverse the rotation of the tap periodically.
7. Use solvent to clean out all of the chips.
8. Apply compressed air with a shop towel wrapped around the air spout, in order to retain the chips forced out of the hole.
9. Tap the hole again to clean the threads. The tap should thread in with little resistance.

Important: Make sure all of the chips are cleared from the hole.

10. Use solvent to clean out all of the chips.
11. Apply compressed air with a shop towel wrapped around the air spout, in order to retain the chips forced out of the hole.
12. Use a flashlight to confirm that all of the chips are removed from the hole.
13. Continue to clean the hole until all of the chips are cleared.
14. Install the heli-coil insert as follows:
14.1. In order to determine the correct size installation tool and length insert refer to the appropriate picture and chart.
14.2. Screw the insert on the mandrel of the installation tool until the driving tang is fully engaged in the driving contour.
14.3. Coat the insert with spray machining oil.
14.4. Install the insert as follows:
14.4.1. Slide the prewinder over the mandrel and insert.
14.4.2. Rotate the mandrel clockwise until 1 or 2 threads of the insert are threaded into the prewinder.
14.4.3. Place the insert in position on the threaded hole being repaired.
14.4.4. Rotate the mandrel clockwise until the insert is flush with the top surface of the threaded hole.
14.4.5. Remove the prewinder except when repairing cylinder head bolts.
14.4.6. Continue to install the insert until reaching the original thread depth.
14.4.7. Remove the mandrel.
14.5. Remove the driving tang from the thread insert as follows. The tang must be removed in order to allow passage of the fastener through the insert.
14.5.1. Place the square end of the punch, no chamfer, on the tang after installation.
14.5.2. Strike the punch sharply with the hammer. The tang will break off at the notch.
15. Clean the hole using compressed air. Take appropriate steps to assure that chips are not blown into the engine.