OLD BIKE AUSTRALASIA: 711960 KRTT 750 HARLEY-DAVIDSON
As the Great Depression hit home and racing budgets
were slashed, the factories moved into C class racing
which became the premier US racing class, and
fuelled an intense rivalry between Harley-
Davidson and Indian.
C class machines were production based side-
valve engines with a maximum displacement of
750cc, or overhead valve engines with a maximum
displacement of 500cc. The rules were amended in
the early 1950s banning overhead camshaft
machines, after Norton successfully raced Manx
Inters at Daytona from 1948 to 1951.
The AMA Grand National Championship series
featured four different types of races; the Mile and
Half-mile held on oval dirt tracks, TT (turning track)
also on dirt but with bends and jumps, and circuit
racing on sealed courses. After the failure of Indian
motorcycles, the Harley-Davidson factory dominated
the series until the early 1960s. British manufacturers
then got into their stride, with BSA and Triumph
winning most of the national titles from 1963 to
- In 1969 new regulations were introduced
allowing 750cc overhead valve engines.
KR Series Harley Davidson
Harley-Davidson introduced the ‘middleweight’ K
series in 1952 to counter the growing popularity of
the lighter and faster British motorcycles. The 750cc
side-valve K-series engine was based on the bottom
end of the previous WL engines, with the same bore
and stroke (2-3/4” x 3-13/16”), compression ratio
of 6.5;1 and aluminium cylinder heads. However the
rest of the machine was a radical departure from its
predecessor; the new unit construction crankcase
housing a 4 speed, right hand foot change, gearbox
and primary transmission. The all-new frame had
hydraulically damped swinging arm suspension and
hydraulically damped telescopic front forks.
Producing 30-horsepower in a bike weighing 400
pounds, first-year K-models were not much faster
than Harley’s 600-pound Panhead.
Harley-Davidson quickly introduced the KR and
KRTT racing models to replace the ageing C Class WR
racers. The factory KR dirt track racer had a bolt-on
rigid frame which allowed riders to switch back and
forth for different types of track competition. The
KRTT used a version of the new road going K series
frame and cycle parts. Besides high-performance
engine parts, hubs, rims, brakes and six gallon tank
were available as factory racing parts. The factory
also produced two further KR variants; the KRM, a
desert racer that was only made for a couple of
years and the KHR an 883cc version for use in some
events that allowed up to 900cc side-valves.
The road-going K series was superseded by the
OHV 888cc Sportster in 1957, but production of the
race-only KR-models continued until 1969. The race
department built small batches of machines each
year, keeping some for themselves and selling the
rest to sponsored riders and dealerships. There was
always a shortage of new machines, so how Alf
Groves in New Zealand was allocated a new
machine is a real mystery.
Over its eighteen year factory racing career the KR
engine was gradually developed, with improvements
being made available to riders each year to keep
pace with the smaller OHV opposition. Dick O’Brien,
head of the Harley-Davidson racing shop, recruited
tuner and camshaft expert Tom Sifton, gas-flow guru
Jerry Branch, and others to help develop the engine
out of all recognition. The factory even developed
different camshafts to suit each of the racing
disciplines. The factory also issued a handbookdetailing how to bring the machine up to the latest
standard and recommendations on how to set up the
machine for each of the disciplines.
The final factory version of the KRTT 750 for
1968/69 had a new “lowboy” road racing frame
and twin carburettor conversion. Dick O’Brien has
stated the greatest power they ever achieved was
58bhp, despite wild rumours of much larger outputs.
In 1964 the AMA lifted a ban on fairings in road
racing, and the factory eventually produced an
excellent road racing fairing and streamlined seat
for the lowboy frame that added 6mph to the top
speed over the previous fairing. The new fairing and
seat were painted in the distinctive Harley-Davidson
orange, black and white colour scheme that is still
used to this day.
The KR 750 was superseded by the XR750 in
1970 but the KRTT remained competitive in road
racing whilst the early iron engine XR750s were
redesigned with better aluminium heads and
barrels. Cal Rayborn rode an outdated KR 750
“lowboy” in the 1972 Trans-Atlantic Match Races
against some of the finest riders in the world on
their latest factory machines. With no experience of
the English tracks Cal won three of the six rounds
and tied for the overall title. ■AMA C Class Racing
In the 1920s and early 1930s the American factories spent small
fortunes racing highly developed prototype machines. To reduce
the cost of racing for ordinary riders and to try and level the play-
ing field, the American Motorcycle Association (AMA) introduced
Class C racing in 1933, based on production motorcycles. The XR750 that superceded the KR 750.
John Shand’s XR750-
KRTT on display in
his living room.