Aluminum Block-Head Bolt Thread Repair

Buy a Manufacture Specific Head Bolt Repair Kit for $450 & Up or Use This Head Bold Thread Repair Method for About $90

We get a lot of calls from people who go to put their cylinder head(s) back on the engine (aluminum block) and the threads strip while trying to torque the head bolts. Let’s talk about the different threads first. Standard “shelf item” metric bolts are 6MM, 8MM, 10MM, 12MM etc., all even numbers. The auto manufactures sometimes use the odd number metric threads on some of their fasteners, 5MM, 7MM, 9MM, 11MM etc. Because of that, the people who make thread repair kits have those sizes. Here’s the rub: most of the threads are recessed down in the block, usually 35MM (1 3/8”) to 51MM (2”). The thread repair kits won’t go down that far. You can buy a Time-Sert kit specifically designed to do this very repair for a meager $415.34 and it includes free shipping! Or you can do it this way and spend less than $40, and it’s easy. If you thread the top of the block with a 11MM/1.5 thread pitch, our example below, you can’t buy replacement bolts that are 11MM X 1.5 pitch the correct length (that we could find) to bolt the head to the block. We install 7/16” thread repair inserts instead. They are virtually the same size, .433” versus .437” and we can buy the bolts in ¼” increments. If I’ve confused you, the following example should clear it up.

This example is a 2001 Toyota Camary 2.4 liter DOHC and the Hondas are very similar. I’m not picking on Toyota or Honda. If we were discussing an in-line aluminum BMW 6 cylinder block, I’d start out saying plan on re-threading the block before you even take it apart (it’s 12MM X 1.5 and you can still use the OE head bolts).

The factory head bolt approximately 6 ½” long, 11MM X 1.5 thread pitch. The threads in the block don’t start until approximately 2 ¼” down from the deck of the block, 4 ½” from the head bolt hole in the head.

This is the factory head bolt:

Here is the new head bolt:

The reason I showed the tap with the new head bolt is a few people have not threaded the hole deep enough. The tap is tapered at the beginning to get it started. If you don’t thread it deep enough the bolt gets tight at the bottom and you can’t get the right head torque, called “clamp load” on the head gasket.

Here’s what you need:

1. 1-7/16″x 14 TimeSert kit P/N 0761. The inserts that come with kit are not long enough, order P/N 076135 (1″ long) as many as you need( a couple extra probably a good idea).  Here is the installation video link if you like: http://www.timesert.com/html/install.html#1
2. Installed properly you don’t need loctite. We buy from Neal @ Mechanics Tools, here’s the link:  http://www.mechanicstoolsandbits.com/
3. Lastly the bolts you need are “Grade 8 Socket Head Cap Screws”. We by the from McMaster-Carr. Here is the link:  http://www.mcmaster.com/#socket-head-cap-screws/=121vu66 .

 Most 11 MM applications take 4″ long, full size such as Camry, Accord etc. Some of the 10 MM applications take 3 1/2″ long such as Civic, Corolla etc.

Here is the block before the repair:

Here it is with the insert installed:

The drill size for the insert is 29/64” (.453”). Since the holes are already .465”, we didn’t even have to drill them. Be sure to use thread cutting fluid or light oil when tapping the threads. Clean the threads with Brake-Kleen or equivalent before using Loctite. In this case you don’t have to worry about where the chips go, these are dead end holes (as most are) meaning they can’t do any harm at the bottom of the hole.

Let the Loctite dry overnight before you assemble. Thread all the bolts all the way through the insert by hand. If there is a bind, remove the insert, re-tap the hole and install a new insert. You can remove the insert by grabbing the end of the top tip of the insert with a pair of needle nose pliers, turning it clockwise wrapping it around the needle nose and spiral the insert out.

The entire job won’t take more than an hour or so. Once you do the first 1 or 2, the rest will go easy.

Hope this helped,
John