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Thread Repair

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Easily and  permanently repair stripped threads using a repair coil. 

There are a few things to figure out before starting on this venture.  The first thing is, if the bolt goes the whole way to the bottom of a blind tap (one that ends in the material with no exit) you will need to use a blind type tap to tap threads all the way to the bottom.  Most taps are tapered at the end to allow them to start correctly. With a normal tap however, the tap will bottom out before making threads all the way to the bottom of the hole, and a blind tap would be used to finish it.  In the case below, this is a blind tapped hole however the bolt that fits it stays well clear of the bottom, so a normal tap may be used to make the threads. 

The next thing is thread size.  The thread size listed on the repair coil is the size of the thread that it is repairing, NOT what size tap or what size the coil fits in. I suggest buying the kit which includes the tap, installer tool and a few coils.

Start by protecting the surrounding areas from metal shavings, this is specially needed while doing work inside an engine.  You will need to remove the old threads and resize the hole with the correct drill bit, usually this is listed on the repair kit. I like to cover the bit with thick grease so that all the shavings stay right on the bit are are easily removed.  Once the hole is drilled, clean the bit, apply more grease and twist it in the hole by hand to remove any other shavings. 

Next tap the hole with the supplied tap, also coating it with grease to catch and shavings. Be very patient while tapping, specially in aluminum as it is very soft.  Make sure you correctly start the tap to keep it straight. Turn the tap 1/4 to 1/2 turn at a time backing it off just a tad each time. Always do this by hand, never put the tap in a drill. Try not to remove the tap once you start as it is very easy to cross thread what you have already tapped.  Once the tap is at the bottom of the hole remove it.  Finish the job with a blind tap if needed.

Next would be to insert the coil in the threads you just made.  The kit I am using comes with a little loader (blue) but some do not.  All kits should come with an insertion tool.  Threading in the coil is as easy as threading it onto the end of the winder tool and then threading that into the hole.  The tail of the coil should be at the bottom of the hole once finished.  Multiple coils may be used one at a time however usually that is not needed. 

Once the coil is inserted make sure it is a few threads past the top of the hole and then remove the tail.  If you can get to it from behind this is very easy to do with a pair of needle nose pliers.  If you are working with a blind tap as in this case a small punch can be used to strike the tail and break it off.  I then used the same tap with a dab of grease to remove the tail from the hole.  If the coil you are using goes the whole way to the bottom of the tap so that the tail is resting on the bottom it may be impossible to remove and most of the time in this case will not need to be removed.  Just make sure it does not interfere with the bolt that will be used.