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In order
for this project to work several criterion needed to be met.
First, the gearbox had to look the same as the original Indian
transmission. Second, the
gearbox would preferably be a constant mesh style as the “crash”
style had too many reliability problems.
Third, the gear ratios of the original three-speed gearbox needed
to be preserved and an overdrive gear added for highway cruising.
Engineering
began in earnest March 1999 with Frank Byford joining the team.
Frank began his engineering career in the 1950’s working and
riding for Greeves Motorcycles in England.
In 1953 he went to work for Associated Motorcycles who built AJS
Matchless, Norton, James and Francis Barnett bikes. One of his first
projects was to design four-speed constant mesh transmission for this
line of motorcycles. Frank’s
designs were very popular in England and emulated by many of the other
motorcycle manufacturers for several years.
The
stock Indian three-speed transmission design was reviewed and the
available space inside the case
checked to see if a 4 speed gear set would fit without compromising the
integrity of the power train. The initial result was that there would be
insufficient room for conventional sliders with dogs. Packaging
was constrained by the engine in the front, the frame underneath and
behind, the generator drive, the clutch on the left and the sprocket on
the right. Many approaches were
considered and several unconventional concepts eventually had to be
employed to cram the proverbial quart into the pint pot.
With some
careful juggling of material, undercutting into some of the gears to use
pockets instead of dogs the design gradually came alive. Using 12
instead of 8 D.P. gears
also provided a little more room, and as a bonus opened up the number of
gear ratio combinations considerably. The
reduced thickness of the teeth would reduce tooth strength so it was
decided that a stronger material was needed to make up for the
loss. After a little research AISI
9310 was selected for both the gears, the secondary shaft and the
mainshaft. This material has a
25% core strength increase and a 3 point case hardness increase over
AISI 8620. The design
was then detailed, the casting patterns purchased and the parts ordered.
The
prototype was completed utilizing an original case with a specially cast
cover made with a homemade pattern. The parts were machined and heat
treated and assembled in record time. This
prototype box was installed on Thaines ’50 Chief at Dave Hansens
“The Shop” in Ventura and a couple of quick test runs made by Thaine
and Dave. With a big Grin
on his face Thaine left for his shop about 50 miles away, being able to
cruise comfortably at 75mph with no problems. Unfortunately
not all went well, a couple of days later Thaine was rammed by a car
changing lanes that made his bike unrideable and Thaine sustained an
injured shoulder.
The box
was removed from the damaged bike and the insides studied for wear and
damage. Although there were only a few miles on the box it appeared that
cruising in overdrive caused some indication of ‘blue shaft’ due to
the output bushing rotating faster than the mainshaft while under load
with insufficient lubrication. This led to opening up a few clearances
and adding figure 8 oil grooves in the output bushing.
This
prototype box eventually ended up on a machine prepared by Dave Hansen
for a second Bonneville speed record attempt in September 2000. After
the record setting run Dave Hanson was asked how every thing went. He
replied, “When you are at Bonneville you don’t have time to be nice
to your equipment, or worry about its functionality.
We abused the four speed overdrive transmission for over ten runs
at top speed and it
performed flawlessly.” The reason that the Chief box was used for this
second run is because the first run was plagued with the machine jumping
out of second gear with the crash box during acceleration. The Chief
box, being constant mesh, did not jump out of gear.
More
thought went into the design and the whole gear cluster was revamped to
use a larger diameter mainshaft. Caged needle bearings were used instead
of bushings and a thrust bearing installed to take care of the axial
thrust caused by operating the clutch. With the use of a bigger
mainshaft and caged needle roller bearings, larger diameter case
bearings were required. This necessitated making an internally beefed up
case casting to accommodate the larger bearings.
Seals
were added to all of the external rotating leak paths and the production
run of 20 started.
The first
production transmission was shipped to Carl Sorenson at Apopka Indian.
Carl installed it in his daily rider, a 1948 Chief.
To date, he has put over 8000 miles on it with no problems.
You can read his and other rider comments on our web page at http://www.chief-overdrive.com.
Carl and three other Chief Overdrive riders took their bikes up
to the Springfield Indian Centennial in July 2001.
The
first transmission design
was for a late model (1940-1953) Chief.
Then parts for the rigid frame (1935-1939) Chief were added to
the inventory. An overdrive unit for the Scout will probably be in the
future plans if there is sufficient demand.
As
Mark Hanlons’ other business interests blossomed, he found that the
Chief project was taking too much time away from them and decided to
sell the project, with the result that in 2002 the designer, (Frank
Byford), and Irongate Machine, (Kerry Byford and Rick Rudy) bought the
project complete. After the Lawyers,
paperwork and all the bureaucratic stuff was completed the current
production run of 50 was started in June 2002 with deliveries the first
week in February 2003.
A
number of wonderful people helped throughout the project for which a
hearty thank-you is in order. Some of those who helped the project along
the way were Thaine Morris,
Dave Hansen, Carl Sorenson, Wilson Plank, Greg Hutchinson, Bob Stark,
Gary Stark; Mike “Kiwi” Thomas; Jerry Greer, Jody van Meter, those
loving and understanding wives, all of the vendors and other
participants, because, without their help and perseverance, the project
would have taken much longer to complete. Bonnie
West has done an excellent job of our website which has had many hits
since it was published.
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