Installing the 66t Rear Wheel Pulley from Vance and
Switching to a 66 tooth rear wheel pulley, with a 30 tooth transmission pulley, will help in pushing
the top end speed of the XR1200 up toward 160 mph, and/or further reducing RPM at highway speeds. A 66 tooth rear wheel
pulley can be purchased from Vance and Hines as an optional item for the XR1200 Race Kit, or can be made from a pulley for
other Harley Models. Information for machining a HD pulley in lieu of buying the part from Vance and Hines
can be found here.
Before one starts this mod, consider this
to help avoid damage to your rear wheel -
Harley's torque spec for the mounting bolts in the rear wheel sprocket/pulley
appears to be set based on providing a strong clamping force by torquing to (or slightly above) the conventional maximum
torque spec of a Grade 8, 7/16-14 bolt. The Grade 8 bolts can handle this torque (provided the bolts
are only used once, as recommended by HD), however, this torque spec does not appear to take into consideration
the potential failure of the threads in the bolt holes in the cast aluminum wheel, due to the lesser yield strength of the cast
aluminum rear wheel and the depth of thread engagement.
While the 1.725" long, Grade 8, 7/16-14 pulley mounting bolts can handle Harley's
specified final torque spec of 80 ft-lbs, the maximum torque calculation for the bolt holes in the cast aluminum rear
wheel with the stock 68 tooth pulley, based on the .845" depth of thread engagement with these bolts, is on the order of 45
ft-lbs. So, while the Grade 8 bolts can be replaced each time, the force on the threads in the bolt holes in the
wheel itself appears to be excessive - and the threads in the bolt holes can fail if 80 ft-lbs of torque is used
during re-installation of a drive pulley.
Additionally, the Vance and Hines 66 tooth rear sprocket/pulley is about 0.365"
thicker than the stock 68 tooth pulley in the hub area around the mounting bolts. That means that the stock pulley
mounting bolts will not seat as deeply into the rear wheel when mounting the V&H 66t pulley. Therefore, when installing
the 66 tooth pulley using stock bolts and washers, there will only be about .480" of thread engagement in the HD/Enkei cast
aluminum rear wheel. According to calculations, this is not enough thread engagement to reliably support the 80
ft-lbs of torque spec'd by HD for the pulley mounting bolts in a stock rear wheel, and there is about a 50% chance that the bolts will pull out of the wheel when torqued to 80 ft-lbs!
I highly recommend using 2.25" (7/16-14) bolts when installing
the V&H 66 tooth rear pulley on a stock HD/Enkei rear wheel. This length will make full use of the threads
in the stock rear wheel and help reduce the liklihood of bolt hole thread failure in the rear wheel when the pulley bolts
are torqued to spec. (Note that if selecting longer bolts they should
be Grade 8 or harder, and if there is an unthreaded shoulder on the shaft of the bolts, it needs to be less than about 1.1"
or there is a risk of bottoming out the shoulder of the bolt before the pulley is tightened down.)
Also, one might wish to consider using a more conventional rear pulley bolt
torque value of 55-65 ft-lbs (as in earlier Sportsters) with Loctite. One just should be aware that according to engineering
calculations, the torque value of 80 ft-lb spec'd by HD for the 2009 Sportster pulley bolts is too high for
the stock Grade 8 bolts when fastened in the bolt holes of the cast aluminum rear wheel.
Now for Installation...
The 66t rear wheel sprocket/pulley will increase top speed on the XR1200, and lower rpm at highway
speeds. It can be used with a 29 or 30 tooth transmission pulley and the stock 1" wide, 137 tooth, drive belt.
If one installs the 66 tooth pulley with a 28 tooth transmission pulley, a shorter drive belt will be needed.
Also, when changing the final drive gearing, the speedometer will need to be recalibrated to remain
First Remove the Rear Wheel
Aside from the fact that it is very difficult to remove and install the pulley bolts with the wheel
mounted, the pulley obviously fits around the rear axle. First, the rear wheel needs to come off.
Remove the stock 68t Rear Wheel Pulley
There is no trick to this, but the pulley bolts are torqued firmly in place. A large breaker
bar on a 5/8" socket will make this easier, as will having a helper hold the rear wheel.
(The goop on the bearing in the picture, is antiseize from the axle.)
|Rear Wheel without Pulley
Stock XR1200 Rear Wheel Pulley
The stock 68 tooth rear wheel pulley weighs about 5.6 lb. The center mounting hub is about
|Hub of Stock 68 tooth Pulley
Vance and Hines 66 tooth Rear Wheel Pulley
The Vance and Hines 66 tooth rear wheel pulley weighs the same as the HD
rear pulley at about 5.6 lbs. The V&H pulley is a HD pulley for a Big Twin that has been machined for proper offset
on the XR1200 (click here for details on machining). Because of its design and different dish offset, the center hub is .880" thick. Even though .38" smaller
in diameter, it is not lighter than the stock pulley..
V&H Rear 66 tooth Pulley Overlayed on HD Stock 68 tooth Pulley
The below is a picture of the two pulleys overlayed on top of each, the stock 68 tooth pulley is
about 0.38" larger in diameter than the Vance and Hines 66 tooth pulley. Just to get an idea, the V&H pulley is
about 11.81"in diameter at the outside edge of the face. The diameter of the pulley across the tops of the teeth is
|V&H Pullwey on Stock Pulley
Install the 66 tooth Rear Wheel Pulley
HD specs first torquing the pulley bolts to 60 ft-lbs, then loosening them 180 degrees, and re-torquing
to 80 ft-lbs. However, especially with the thicker hub of the V&H 66t pulley, I suggest using longer grade 8 bolts
to reduce the chance of damaging the threads in the rear wheel bolt holes. I used 2.25" long stainless steel 12 point
7/16-14 bolts One might also wish to consider using the "old" Sportster torque spec of 55 - 65 ft-lbs with
some loctite on these bolts to reduce the liklihood of thread failure in the bolt holes of the rear wheel. Again, having an assistant hold the rear wheel is a big help.
Re-Install Rear Wheel Pulley and Adjust Drive Belt
I won't go through installing the rear wheel, tensioning the belt, and aligning the wheel, but again, having an assistant is a great help when positioning the wheel, installing the brake caliper, and positioning
the drive belt and wheel spacers.
One thing to watch is the clearance between the brake caliper bolt mounting bolt and the
bottom mounting bolt on the left shock. If installing the 66 tooth pulley with a 29 tooth transmission pulley and stock
drive belt, the clearance between these two bolts will be very close. With a 30 tooth transmission pulley there wil
be more clearance.