The Indian cams here are mostly for Sport
Scouts as that is my main interest. Chief cams are the same grind in many
cases, but the cam follower (lift) geometry on the Chiefs may change both
valve lift numbers and timing. Included here is also the data for the Ollie
Chief cams with standard Chief lifts.
As you will see from the data, the valve
lift and timing depends on the geometry of the cam followers, or lifts,
as the parts book has it. The Scout lifts changed over the years. The overall
shape got smoother in 1940, pre-40 lifts are angular and chunky, and the
distance (see lower picture to the right of here) between the centre of
the pivot and the centre of the roller changed as well on a couple of occasions.
This is what determines the differences in timing with each of the cams
in the chart below. Bonneville lifts for Chiefs differ from standard on
both the intake and exhust lift. On Scouts only the exhaust lift is different
on Bonneville engines, shorter than the standard lift (Bonneville exhaust
lifts can be either old style 1939, one year only, or late style 1940-up).
The intake lift is the same on both models.
Intake measurements are taken at .006"
lift, exhaust at .008".
There were 3 types of exhaust lifts, with
varying distance between pivot and roller but only one intake. These may
be mixed to give some interesting results... If that doesn't suit your
needs, several of the old-time racers used to heat and bend lifts to get
the distance they wanted. Holes for the roller rivets can also be welded
up and re-drilled to change the lift ratio. This is the case with the special
short intake lift in the tables.
Note that the Bonneville cams don't time
out exactly as the printed info on them. With the Four Cam setup, they
drove the exhaust valve (with new lobes for the intakes), and the timing
was very similar. The big deal with the Four Cams was the greater lobe
separation possible. The most efficient flathead engines (so far!) were
the KR Harleys, and to match the cam timing of these in a Scout, four cam
lobes will have to be used. More about that another time...
on pictures to see full size!
Top row: Up to 1939 Scout
Bottom row: 1940-up lifts
Distance between pivot and
roller determines timing and valve lift
|Long IN (STD)
|Short IN (Special)
|Long EX (STD)
|Med EX (Early)
|Short EX (BON)
For more Indian cam pictures,
please go to the VI Photo Album here.
On the Cam page in the Album, you'll also find more lift info as well as
info on four-lobed racing cams. And there's more about the Four Cam System