How to repair pulled out or stripped head bolt threads in an engine block: BMW M52, Northsar, 2AZ-FE and all other aluminium and steel blocks

So you’ve stripped the threads in your aluminum block? Don’t worry, here are three different kits to help you make your threads stronger than before.

With the increase in the use of aluminum in engine blocks, there has been a significant increase in head bolt threads being pulled or stripped out.

There are many different styles of thread repair inserts available, but for something as critical as a headbolt, there are only three kits I recommend.

1. Lock N Stitch Full Torque Blind inserts

These are the only inserts that I am aware of in the market that have a “blind” or enclosed bottom to them. This is extremely advantageous when you are dealing with modern day blocks that have coolant passages running directly under or right beside the bolt hole threads.

Illustrated here, you will notice that the coolant channel runs directly under the bolt holes on some blocks (m20b25 ironblock pictured).

Blind bottom illustrated:

Further, unlike other inserts, this type of insert pulls the metal surrounding it towards it when installed instead of pushing it away; notice the angle of the external threads:

Installation procedure:

Other major advantages include a mechanical locking pin after installation as well as the ability to order custom sizes.

2. NS300L By Huhn Solutions

A nice lower priced kit, that includes everything you need and uses a beefy coarse thread insert.

One downside with this kit is that the insert is held in place with red loctite. In the real world, the loctite is good to 260C or 500F, with engines operating at less than half of that. However a mechanical locking method is always preferred to a adhesive method (as it can be doubled with red loctite).

3. Time-sert and Big-sert

Comparable to the Nuhn kits at higher price. Two types of kits exist; a normal level Time-sert kit and a second kit called the Big-sert kit. A Big-sert kit has the same internal thread diameter as the timesert kit, but a larger outer diameter, to allow fixing of a hole that has been fixed or attempted to be fixed in the past.

Big-sert kits are inherently stronger because they grip into more material, however, if they fail there is no third level.

Choosing between starting with a time-sert or big-sert is an individual decision, however I recommend starting with a time-sert if its a iron block you are working with and a big-sert if its an aluminum block you are starting with.

The primary advantage of a time-sert or big-sert kit is that the insert mechanically when the installation tool jams the lower threads into the base material:

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