Understanding the combination Starter Generator

[ROD W]

I know a number of people with pre 1925 Buicks,  on this Forum  have done a lot of work on their starter/ generators  and have a good knowledge of there workings,  But I would like to give a step by step explanation of the S/G for those who find them a bit of a mystery.  I am not an auto electrician,   but have been lucky enough to be able to play around with these S/G for close on fifty years.  My experience has been on the S/G from the late teens and early 20,s,  so the earlier one,s starting in 1913/14, will look slightly different  but function in the same way.  I will include a bit of physics to help understand the workings of a DC Motor.

All this information is available in the Buick Reference Books and Workshop Manuals for each year,  but can be fairly difficult to follow.

As stated it is a combination  Starter motor and Generator  and has three functions.

1-  Starter Motor to crank the engine.  

2- Generator to recharge the battery and provide for the lights

3-  The Generator also acts as a motor to align the gears that connect to the flywheel for the starting operation.

 

The s/g has two basic components   1.  The iron frame which provides the magnetic field and  2. The Armature that rotates in the magnetic field.

 

 

 

DC  MOTORS

When a current is passed through a conductor in a magnetic field,  it experiences a turning force

 

 

In the Delco  s/g  there are two field coils.   One for the generator motor ( this is a shunt motor,  meaning the field windings are in parallel to the armature ) and another for the starter motor.( whose field windings are in series with the armature )   The armature also has two sets of windings ,  one for the starter motor  and one for the generator,    with their respective commutators.

The two motors operate very differently due to the positioning of their field coils.

 

STARTER   MOTOR

This motor has the field coil in series  with the armature.  

When the field coil is in series it requires a load to limit the speed of the motor.  In our case the cranking of the engine provides this load  to stop the starter motor turning too fast.   If you bench test the starter motor,  only provide power for a very short time so the motor is not destroyed by spinning too fast.

 

GENERATOR  MOTOR

In this motor the field coil is in parallel with the armature

 

The advantage of this is that the motors speed is self  regulating,  so it will not get faster and faster,  It does not need a load to slow it down.  This is evident when the ignition is turned on and the generator can be heard motoring.

 

1918  -1921 S/G

1922 -1925  S/G

 

1925 Armature with both starter commutator and generator commutator,  , inside  Iron body showing iron core  that field windings  wrap around.

 

 

Edited May 28, 2018 by ROD W (see edit history)

[Mark Shaw]

My 15 Model 25 Buick starter "motors" when I turn on the ignition and will spin when I push the starter pedal, but it will not crank the engine. 

Are the clutches adjustable?

[ROD W]

Mark,   On the 1920 and I feel the 1915 would be similar,  there is adjustment on the shaft  that engages  the starter gear,  with a lock nut.   Maybe the locknut  is loose  and the lever is sliding on the shaft.   There is also a small amount of adjustment on the shaft that engages the starter brushes.  This lever simultainiously  engages  the starter gear and the starter brushes.

Edited May 29, 2018 by ROD W (see edit history)

[ROD W]

On removing the screw,  found it does not allow for adjustment  but  a  location pin to align the lever in the correct position.  But if this pin has come out or is loose it would allow the lever to slide on the shaft.

Edited May 29, 2018 by ROD W (see edit history)

[ROD W]

Even though the 1915 has the starter commutator at the back of the s/g and the generator commutator at the front of the s/g  it still has a similar set up to engage the starter gear and the starter brush.   Also check that the one way clutch is actually working.   Turning in one direction and locking when turned  in the opposite direction.

 

 

 

Edited May 30, 2018 by ROD W (see edit history)

[Terry Wiegand]

Rod,

I really like the way that you have taken things apart, photographed, and labeled the different parts and pieces.  What you are calling the one way clutch,  I have always heard referred to as an overrunning clutch.  Again, I really like what you did here.

 

Terry Wiegand

South Hutchinson, Kansas

[ROD W]

Thanks  Terry,    I just use the name that  sounds appropriate at the time.   I should look up the manual for the proper name.

[AussieBuick]

Rod thanks for post it I was beginning to think you needed. Ph.D.  To work on this.  Regards Norm

[Mark Kikta]

Thanks for these details Rod.  I have my Starter/Gen on my workbench today to begin taking it apart to clean and checkout.  Perfect timing for me.

[DonMicheletti]

Matt,

Perhaps to stste the obvious, are the starter brushes dropping and contacting the starter commutator?

[Hubert_25-25]

Mark, 

     This Starter Generator is slighlty different than yours since it is newer, but much of what I have written in this rebuild procedure is applicable.   Hugh

 

[Mark Kikta]

Great information also Hugh.  Timely for me but my 22 is a bit different

 

Regards,

Mark

[Oregon Desert model 45]

1924 & 1925 Master brush adjustment can be made by spinning the linkage push rod while the linkage assembly is removed from the motor.

This will allow for correct sequence of Overrunning clutch engagement to flywheel teeth just as the starter brush drops.

Push rod is fully unscrewed exposing the threads in second photo below

Kevin