How to repair a stripped thread with HeliCoil/BaerCoil from a Suzuki Bandit 600 valve cover cam cap bolt to avoid oil leaks through the gasket

During the last valve job on my Bandit, I stripped a few too many threads from the valve cover mounting holes. The consequence was oil leakage on the left side of the valve cover gasket. Although only 3 threads got damaged, I decided to repair all 8 of them. The steel bolts in the soft aluminum are guaranteed to strip sooner or later.

How to mount a coil insert from Baercoil
(European Helicoil alternative)

The usual solution for a stripped thread is to bore out the hole and tap a new thread of the next bigger size. After this, just go and find a bolt of this new size and you're all set. In my situation I couldn't use this solution since the bolts that hold down the valve cover of my Suzuki Bandit have a special head shape that mates with the gasket used to seal the cover.
A better solution then going to the next oversized hole is to repair the existing thread with Baercoil inserts (in the US these are called Helicoil inserts). After the repair the original bolt can be used, since the repaired hole has the same size of thread as the original hole. Another advantage is that the repaired thread will be much stronger then the original one was. That's why this system is used, not as a repair but as an original installation, in aircraft engineering.

A few simple steps 

(or check out "what to do when things go wrong" at the bottom of this post)

First, I had to open up my engine and remove the first cam cap. This is an easy repair, since the valve cover is not attached directly to the engine head but is mounted using a hole in the caps that hold the camshaft. So we just need to remove the camshaft. You can see the bolts partially unscrewed on the first cap I will be taking out. Be carefull to replace the caps in their exact same position. They are not interchangeable, since the caps have been machined to match with the camshaft. (This is also why it's not possible to buy replacement cam caps. If you ever need to replace them, you need to replace the complete engine head!) To avoid mixing them up, I unmount and remount them one by one.

This is a picture of the first cam cap removed. Make sure the leave the bushes in their seats and to not move or touch the camshaft. Any dirt you get on it will grind between the camshaft and the cam cap.

Put the camp cap between a bench vise. Make sure you mount it straight and level. I use a few pieces of cardboard to avoid scratching the cam cap.

This is the Baercoil set I ordered from eBay (link august 2012). Make sure to get an M7 x 1,0 (this is a very rare size).

The set contains a drill bit, special Baercoil tap, insert mounting tool and a shaft used to break of the small tang in the center of the coil. The other bits are the actual coils that will go into our hole to be repaired.

The first step is to drill out the hole. Make sure you hold your drill very straight in all directions when you do this with a handdrill. I noticed it is much easier to drill when you set the speed on very slow and only drill one (or even 1/2) turn at a time. So I was actually drilling almost by hand, just using the torque of the drill at 0 rpm. Then I back up a little and I advance again for a bit. Once I reach the bottom of the hole, the drill turns freely. I also added a bit of cutting oil to facilitate drilling. After drilling, I clean the hole with some paper and I blow it out.

The actual cutting of the thread is the easiest and most fun part. After wetting the tap with a bit of cuttinf oil, I position it straight on top of the hole. By applying a bit of pressure, the tap will pull itself straight in the hole. After 3 turns I back out 1 turn. Then I continue with 3 turns, 1 turn backed out.

After the initial 3 turns when I feel the tap has started cutting I don't apply pressure anymore. I make an effort to evenly push left and right on the tap handle in order to maintain a straight angle. (BTW, the tap handle is something you need to buy separately. I still had one from a thread tap set.) When the hole is halfway tapped, I add a bit of cutting oil. After the hole is made and the tap is removed I clean the new threaded hole with some paper and I blow it out. Then I clean the tap and turn it all the way in and out once more. This is to clean the threads, so I avoid the Baercoil spring to be seated badly.

Next you need to insert the coil. Slide the coil over the mounting tool with the tang in the slit at the bottom of the tool. Do not remove the collar on the tool (read on why).

I added a bit of green loctite to the outside of the thread insert. This is to avoid the coil from unscrewing itself when I remove the bolts during the next valve job.

When inserting the coil, make sure to always keep pressure with the collar of the tool on top of the coil as long as you're turning. Also: never back up. It's not critical how you position the coil over the hole, but make sure the mounting tool is held straight and some pressure is applied whilst turning. Turning should be done slowly to avoid the coil missing a thread or breaking of the tang with the tool.

This is what the repaired hole looks like.

We still need to break off the little tang at the bottomof the coil that was used to grip the mounting tool. A light blow with a more or less heavy object on the shaft that is delivered for this purpose with the kit will break it of. Blow it out or hold it upside-down to remove it.

A step not to be forgotten: clean the bolt that will go in the thread. You can see how much aluminum was caught in the threads of this bolt. I use some cutting oil and some paper to completely clean the bolt. I place my fingernail at the start of the thread and then completly 'unscrew' the bolt.

As a last step before remounting the cam cap I test if the bolt will turn effortlessly in the new thread. Ready!

When things go wrong with the thread insert & how to remove a failed insert

On my second hole, I had a not-so-brilliant idea: I removed the collar around the coil mounting tool. I figured this would make it easier for me to see when the coil was turned all the way in (+1/2 turn). However, this causes the tool to pull (using the tang) on the bottom of the coil instead of pushing it from the top (using the collar).

The result was an insert that couldn't hold a bolt. The threads were 2 thread-widths aparts at the top of the insert. On top of that, I had already broken of the tang before I noticed things went wrong. (In retrospect, I doubt turning anti-clockwise with the mounting tool would have had any effect, besides breaking of the tang anyway).

To remove the failed coil insert, I tapped for 2 turn in the baercoil insert itself. This broke off some material, but also made the end of the coil point upwards so I could grap it with a pair of pliers. Using the pair of pliers, I slowly pulled out the coil in a spiraling motion. The coil became about 5cm long in this process, but I managed to remove it completely.
After cleaning the threads by screwing the tap all the way in and out again I successfully mounted another coil insert. The only disadvantage was that it had to be mounted a little bit deeper since the first 2 rows of thread got damaged during the removal.