Aluminum heads are fairly common these days.  Since the bolts are now harder than the object into which they’re threaded, applying too much torque results in the threads being ripped right out of the aluminum.  Now you can’t tighten things back up and you’re in trouble.  Fortunately, this happens enough that there is a commonly available solution to the problem.  It just takes a little patience and time.  Here’s how to repair a bolt hole with a Helicoil.

Any mechanic worth his salt will tell you that you should always adhere to the torque ratings for your connections detailed in the service manual, but if he can tell you with a straight face that he, himself, breaks out the torque wrench for every bolt, he’s a better man than I.  In the case of this 4G63, Keith and I removed the valve cover to discover that the previous owner hamfisted most of the valve cover bolts, leaving us with a lot of RTV to remove and two stripped bolt locations.

This write up assumes that you’ve already know the size and pitch of the bolt for this location and have sourced the right kit for the job.  Even so, it is very important that you double check that you have both the right sized drill bit, tap and Helicoil kit for the job.  If you screw this up, chances are good you’re going to have to scrap the part.  In this case, replacing a head is not something we want to get into.

Since we’re drilling into an installed head, fully loaded with cams and all that, we don’t want tiny metal chips and shavings getting into places they shouldn’t be (namely, anywhere between the valve cover and oil pan), so the areas around the holes to be repaired are taped off and then paper towels were taped into place over the entire head as a preventative measure.  (Already, this is more effort than simply getting the torque wrench, isn’t it?)  The depth of the hole to be drilled is roughly measured, then a piece of tape is wrapped around the specified drill bit to gauge how deep the rabbit hole goes.

The tape and paper towels should do a good job of keeping the metal chips from falling into the engine, but it’s good to have a shop vac handy to be certain you’ve got them all cleaned out as you go.  It would sure suck to have a breeze kick up as you’re carefully removing the paper towel, tossing that engine killing debris right into the engine anyway.

With the hole drilled and cleaned out, the next step is to use the specified tap to thread the hole to accept the new Helicoil.  You want to be sure to lubricate the tap with a good cutting oil.  WD40 might be okay, but I went with this random bottle of Slick50 One Lube because it was thicker than WD40 and could be applied in strategic drops where I wanted it.  Thread the tap into the hole, making sure you turn it back and forth as you go.  A good rule of thumb is a full turn in, then half a turn back, full turn in, half turn back, and so on.  This ensures the tap stays lubricated and cuts clean.  Trust me.  You don’t want to break a tap off in this hole.

After backing the tap out and using your shop vac to get as much of the debris out of the hole as possible, you might want to give things a couple quick shots of compressed air to really make sure things are clean and ready to go.

The Helicoil will have a “tang” on one end.  You thread the coil onto the end of the installation tool (which resembles a bolt at one end) until the tang engages the tip of the tool.  Can’t see how the coil engages in the picture above, but you can see the tang.

Carefully start threading the Helicoil into the freshly tapped hole.  You should not need to use any other tools to spin this guy down to a thread or two below the surface.  If you do, remove the coil and chase the threads again with the tap.  Otherwise, you should have no trouble threading the insert into place by hand.

With the insert where it needs to be, back the insert tool out (unscrew it, basically), slip the breaker tool into the hole.  It will rest on that tang going across at the bottom.  Give the metal rod (or suitable punch) a nice whack with a hammer to break the tang off.  This will make sure your bolt will be able to reach all the way through the insert if needed and prevents backing things out together.

Grab the bolt and make sure it will thread in nice and clean before you remove your masking tape and paper towels.  If it doesn’t go in nice, you’ll want to be able to get right back to work without having to replace all that masking material.

If you’re sure it’s all good, remove the masking material and thread in the bolt (or, in this case, stud) that goes there.  Remind yourself that it might seem inconvenient to have to go find your torque wrench in the moment, but stripping just one hole because your calibrated elbow is in need of calibration makes for more work.  It’s more fun to modify cars than to fix them up over and over again.

With the hole repaired, it’s now possible to tighten all the bolts in sequence (with the torque wrench, of course) and make sure your valve cover doesn’t leak all over the place.  Shown here is the 4G63 going into the unbadged Galant VR4 on the lift at the shop.  It’s all stock, save a 16G turbo.  (More on this project to come!)