View Full Version : Helical splines for linear motion (Bendix Drive)

11-29-2014, 10:48 AM
For a given diameter of shaft: when
planning a helical spline in an application
with the objective of providing linear motion,
what considerations influence the number of

For instance, to enable the pinon gear of a
Bendix Drive on a starter motor to advance
along the armature shaft, engage with a ring
gear and then retract back to its initial

In general terms, will a greater spline count
produce more bearing surface for smoother
travel at the expense of reduced torsional
strength and increased mfg cost?

The back story here is that a change-up p/n
for a replacement pinion for an old ('70s)
Bendix for a Tecumseh (Toro) starter turns
out to have 7 helical splines, instead of 6.

Looks right with the correct gear tooth count
and slips right onto the armature like it
should, just doesn't engage w/ the helical
portion of the shaft.

Sourced from a local Tecumseh rep, though
with the company long departed, I suppose
all parts now are aftermarket. Looking online,
I have not come across a single instance
where spline count is given in the description
of parts purported to fit.

For a fixed shaft size, by the 70's and beyond
one would think there would have been some
standard settled on, obviating the need to
mess with spline counts.