How To Utilize Thread Inserts To Repair Your Stripped Engine Block


If a head bolt pulled straight out of the engine block during the torque sequence, you will need to take action to restore the threads. One effective way to restore threads in your engine block is by utilizing purpose built inserts. The thread inserts allow you to use the stock size head bolts to prevent the need for making changes to the bolt passages in the head. Furthermore, the thread inserts are strong enough to withstand auto manufacturers' high torque requirements for head bolts.

If one of your head bolt threads stripped out, you can assume the others will soon as well. You should treat all of the head bolt holes the same by installing an insert in each one. Here's how to complete this repair process.


To prepare, gather your metric or standard tool set, drill, air compressor, and insert installation tools to have everything on hand before you start. Obtain high quality penetrating oil for use on the drill and tap for cooling and lubrication purposes. You should tape over the coolant passages and cylinders with contact paper or duct tape to prevent metal shavings from falling in those holes.

Drill Out Old Threads

Working from the upper left hole, align a guide jig on the deck surface of the block using the adjacent holes. Apply penetrating oil to the drill bit and position it over the hole. With the drill continuously running, push it gently into the hole to about halfway. Pull the drill out of the hole and clean it off with a spray of air from the compressor nozzle. Reapply the penetrating oil and resume drilling the same hole until you reach the bottom surface. Repeat until all of the holes are drilled.

Tap The New Holes

Use the air compressor to blow the metal shavings out of the holes. Attach the tap to a T-handle or tap socket. Use the guide plate to keep the tap aligned straight up and down with each hole. Apply penetrating oil to the tap and drive it into the head bolt hole to create new threads. Repeat until all of the holes have new threads.

Install Thread Inserts

Since the new threads are larger than your stock head bolts, you will need to install thread inserts to finish this repair. You simply place the insert on the end of the installation tool and wind it down into the bolt hole until it bottoms out. Give another ¼ turn to seat the insert and pull the installation tool out of the hole. Repeat for all of the head bolt holes.

After you finish this process your engine block is ready for the reassembly process. You can approach reassembly like normal using new head bolts and the manufacturer's recommended torque specifications. Use the recommended number of torque steps to avoid stretching the bolts too quickly, as that could cause the hardware to snap under pressure. 

For more information, contact a local repair shop like Arringdale's Engine Rebuilding & Auto Repair.


16 May 2016

Keep Your Vehicle Safe

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