Kenmore 158: Motor, Belts, and Pulleys

The Kenmore Model 158 sewing machine contains a 120 VAC / 1 A motor that powers all the moving parts through a V belt:

Kenmore 158 - AC drive motor - overview
Kenmore 158 – AC drive motor – overview

Looking up through the body:

Kenmore 158 - AC motor and belt - bottom
Kenmore 158 – AC motor and belt – bottom

A double pulley on a jackshaft reduces the motor speed on the way to the handwheel:

Kenmore 158 - handwheel - jackshaft pulley
Kenmore 158 – handwheel – jackshaft pulley

The motor and handwheel turn counterclockwise in normal operation, but can be turned clockwise by hand as needed. The belt tension isn’t very high and the jackshaft pulleys can slip, but I’m not sure if that’s intentional or the result of several decades of runtime.

Despite the cogged belt, the pulleys are smooth; it’s not a positive-drive transmission with timing-belt pulleys.

The belts:

  • Sears part numbers: top 30083, bottom 28908 / 50013
  • 6 mm at the top of the pulley
  • 4 mm at the base of the V
  • 3.5 mm thick

You could, if you had to, run a belt from the handwheel directly to the motor, although the pulley would ride about 7 mm further out on the shaft. I have no way to measure the lengths with any confidence in the results; one could calculate the lengths based on pulley diameters and center spacing.

Sticking retroreflective tape on the pulleys and handwheel, then deploying the laser tachometer, provides some minimum and maximum speeds:

  • Motor: 2100 – 8500 rpm
  • Jackshaft: 800 – 3200 rpm
  • Handwheel: 200 – 930 rpm

Those aren’t entirely consistent, because I’m using the old foot pedal speed control with its defunct carbon disks; the low end, in particular, isn’t as slow as it can go.

In any event, there’s about a 10:1 speed reduction from motor to handwheel.

The motor label clearly states that it’s 100-120 V AC, but it has brushes, so it’s actually a universal-wound motor that should run happily on DC.