What happens if one strips the threads in, for example, the rear wheel pulley bolt holes?


The threads in two bolt holes stripped as I was installing a pulley on this wheel.  I've commented on this elsewhere, but in essence I believe it was due to the HD specified 80 ft-lbs of torque for the Grade 8 bolt used in the pulley being excessive for the short thread engagement of the bolt holes in the A356 cast aluminum rear wheel.  80 ft-lbs is almost twice the maximum torque spec'd for the yield strength of A356 with these parts, and while HD calls for discarding the Grade 8 bolts after each use, this high level of torque would be repeatedly applied to the much softer bolt hole threads.  Bolt hole thread failure in the rear wheel would seem to be likely during pulley re-installation.  The liklihood of failure is even higher if installing a pulley with a thicker center hub (like the V&H 66 tooth pulley) using the stock bolts and the HD specified torque.


The picture to the right has a view of threads both in a good bolt hole, and in a bad. 
Below are pictures of a bolt hole that had the threads fully stripped out of it, and the threads that pulled out in an even coil.  The coil of stripped threads is about 1/2" long.

0.480" of stripped threads



Another Bad

To the right is a picture of another bolt hole with threads that were severely damaged, although not stripped out entirely.

The ideal repair for a wheel is to replace it.  That said, economics sometimes come into play.  The cast aluminum rear XR1200 wheel is actually a pretty good wheel and at a discounted price of only $270 (List $317) replacement is relatively economical.  One needs to balance alll costs in weighing whether to repair it or replace it.    Helicoil kits with the installation tools and 18 inserts (including long coils) can be purchased through discounters for about $60.   Individual solid thread inserts and their driving tool are also available.
If one already has tools and some basic mechanical skills, a thread repair is a pretty easy task - but then one does need an electric drill, tap handle, lubricant, and misc shop supplies.  On the other hand, a new wheel will require installation of the wheel bearings and internal spacer, and mounting and balancing of the tire.  An assembled new stock rear wheel with the misc parts could still cost $450 - $500 depending on where one gets parts and labor.  Thread repair can be done for less than $75 on the existing wheel if one already has a good toolbox.  The recommended approach for repairing stripped threads in the rear wheel is of course to replace the wheel, but if one decides to repair their wheel here is a look at the typical steps...

Helicoil Thread Repair
Using a Helicoil to repair a stripped thread is relatively easy.  One selects the appropriately sized coil for the bolt, drills the bolt hole to the proper installation size, taps the hole for the outside dimension of the coil, drives in the coil to the proper depth, and the repair is finished.  It takes a steady hand (and/or a drill press or drill guide) to center the pilot hole, and some basic mechanic skills but is not a difficult repair.  There are other solid threaded insert options, but the use of a Helicoil can be very effective for a wide range of repairs.  For this repair I used a 7/16-14 threaded Helicoil, 0.875" long.  (.438" and .656" lengths are also available but because of the torque on these bolts I used the longer coils.)  The following is a look at the repair process...


Drilling the Pilot Hole
The first step is to drill a slightly over-sized hole which will be tapped to thread in the repair coil.  After cleaning any debris and loose material out of the hole, one can use the properly sized drill bit to enlarge the hole.  The pilot hole dimension is specified for the helicoil chosen, and some kits include the proper drill bit.  For a 7/16 - 14 threaded Helicoil, the pilot hole is 29/64".
In the case of the XR1200  the threads in the pulley bolt holes are recessed about .25" inside the hole, and it turns out that the opening of the holes is already 29/64".  This makes centering the drill bit a snap.  Otherwise, one might want to use a Unibit to start the hole and ensure that the regular drill bit does not walk.  In the XR1200, one will end up just reaming out the old threads when the pilot hole is drilled, and not enlarging the diameter of the bolt hole opening.
Even for a skilled mechanic, a drill guide or drill press is an excellent idea to ensure that the hole is centered and straight. 

Tapping the Hole
After drilling the hole and cleaning out the metal fragments,  the hole needs to be tapped for the Helicoil.  The Helicoil kit will include the proper tap - which will not necessarily be a standard size since.  Its thread pitch will match the threads being repaired but its diameter will be sized for the pilot hole.   With large diameter taps, a large tap handle makes the job easier.  Like threading any other hole, plenty of lubricant should be used and the tap should be reversed every few turns to break up the coil being removed.  In a deep hole like in the rear wheel, I will remove the tap a few times during the process and clean out the metal fragments from the hole and channels on the side of the tap to help ensure that the new threads are cleanly cut. 


Tap with Oil

Clean the Tapped Hole
During and after tapping the hole, one will want to thorughly clean out all of the metal fragments.  I use a vacuum during the process and towels afterwards to wipe off the excess cutting oil.  I also clean the tapped holes with brake cleaner to remove traces of the cutting oil prior to inserting the Helicoil.

Clean out threads

Helicoil on driver

Inserting the Helicoil
For a coarse thread Helicoil like is used in the pulley bolt holes, the coil is threaded on to its insertion tool and then the tool is used to drive the coil into the hole.  The insertion tool fits the internal threading of the coil and engages a tang at the end of the coil.  In effect, the coil is pulled into the hole, instead of being pushed into it.  Because of the design of the coil and the fact that it is slightly larger in diameter than its hole, it can not be pushed into place.  Likewise, if properly installed, a Helicoil will not back out when the bolt is unthreaded.  Although not shown here, I also used red loctite just for an extra measure of permanence.  Since the threads in the original pulley bolt holes are recessed about .25" inside the openings, after threading the Helicoils flush, I threaded them in slightly farther to match the threading in the undamaged holes.

Insert Coil

Remove the Driving Tang
After threading the Helicoil in to the proper depth, the installation tang is removed.  The kit will include a metal rod that is slightly smaller in diameter than the inside of the coil.  One inserts the rod and strikes it sharply with a hammer, which will brake the wire at its notch.  After removing the loose piece of wire, the repaired thread is ready for use.

Remove tang

Installed Helicoil
After installing the coil and removing the driving tang, I'll double check to make sure that there is no debris in the new thread, and use some Q-tips to wipe out any excess loctite.  In this case, I'll let the loctite holding the coil dry in place overnight before re-assembling the wheel.  (Again, the loctite that I used during installation should really not be needed due to the design of the Helicoil, but it makes me feel better.)   Here is a look at the repaired threads.


With the long Helicoil that I selected, thread engagement  of the repaired holes will still be at least as long as with the original threads.  Plus, I will change to longer bolts and reduce my final torque for the bolts to 65 ft-lbs, in line with the older Harley spec for these bolts.  Personally, I would rather loctite the bolts into place, than over torque the threads in the cast aluminum wheel - based on the yield strength of the A356 Aluminum used for the wheel and the depth of thread engagement of the much stronger Grade 8 bolts. 
The below is a picture comparing the stock length Grade 8 pulley bolts (nominally 1.725" long) to some 2.25" long, hardened stainless steel, 12 point bolts from Diamond Engineering.  Even though the thread length is nominally the same on the two bolts, the longer shoulder on the diamond Engineering will fit within the thicker hub of the V&H 66 tooth rear pulley and the thread engagement will be 1/2" longer than when using the stock bolts.  (Unfortunately the 2.25" DE bolts cannot be used with the stock 68 tooth pulley because of the thinner hub thickness, but 2.0" bolts can be used, which will provide another 1/4" of thread engagement, and of course, a much better looking bolt head.

Bolt Comparison

Bolt Heads

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