TECH TORQ
details. They too mentioned
the crank runout issue.
My question is if the combi-
nation of crank shaft and
splined shaft machining toler-
ances can exceed 0.003in run
out when leaving the factory,
how can you improve that?
If you bought a new spline
shaft, you could find the same
degree of runout when assem-
bled with the crankshaft.
Let’s look at extremes, a
gear tooth (helical or straight
cut) will run between the two
teeth in the meshed gear. So
left/right lateral positioning
is controlled. This leaves the
up and down positioning. The
gear tooth can only sit as low
in the meshed teeth as the
clearances permit, so this just
leaves the upward movement
in the run out.
So it sounds to me like
Harley-Davidson are scare-
mongering to some degree to
discourage you from fitting
S&S aftermarket parts.- Harry
I ran your email query past
Mark Hood, long-time engine
builder and repairer who
specialises in Harley-Davidsons.
“Doc, crank run out is
an issue. It does not affect
all engines but is a known
condition. The factory has
a pretty generous allowance
regarding the total run out they
consider within specification.
The chain drive accommodates
this situation within reason;
there are a lot of engines
out there that have the issue
without affecting the riders
experience on the bike. Usually
it may only be detected when
an engine is disassembled for a
given reason, be it performance
work or repairs.
“Gear drives are an obvious
answer to wear issues in anydrive situation regardless of
application, but come at a
cost premium and also need
different fitment requirements.
The .003in is nothing to a
chain drive but represents an
excessive variable gear mesh
engagement environment that
has the possibility of backlash
noise if it is an open clearanceand gear tooth damage if it
is an over engagement or
interference situation. There is
no box of shafts to select from,
as your writer suggested.
“The Harley-Davidson
crankshaft is not assembled
from separate shafts and wheel
assemblies, the shafts and
wheels are forged as a singularFull Dyno Tuning and
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