Author Topic: LD1 Start-O-Matic solenoid information wanted  (Read 3513 times)


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LD1 Start-O-Matic solenoid information wanted
« on: October 01, 2019, 10:00:29 AM »
My LD1 SOM is missing many bits and pieces including the fuel control and decompression solenoids. Because these are scarce to find, I would like to try to substitute some modern ones, at least for the time being. Could someone please tell me the stroke length of each.

I would also like to fabricate the round covers for the solenoids and would like some approximate measurements such as diameter and height of these, please.



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Re: LD1 Start-O-Matic solenoid information wanted
« Reply #1 on: October 18, 2019, 06:31:47 AM »
I don't know anything about the LD1 Start-O-Matic, but I have a SR-1 remote start
Kohler generator and have a lot of trouble with the solenoids.  I ended up replacing
the decompression solenoid and doing extensive modifications to the fuel solenoid.

1. Decompression Solenoid

* Type: pull
* Power: AC (not DC!)
* Voltage: your generator's single-leg AC volgage (120 VAc in USA)*
* Frequency:  your generator AC frequency (60 Hz in USA)*
* Duty cycle: continuous (energized whenever engine is running)
* Stroke: ___  inches**
* Force: :  ___ foot-lbs (decreases with distance)**
* Mounting bracket: ______**
* Fastener at end(s) of core: _____**

** Measure for your engine and control linkage.

On the SR-1 Kohler (and I suspect on the LD1) the decompression  solenoid is AC-
powered.   When a certain RPMs is reached, the AC from the generator has enough
power to close the solenoid (which is pulling against a spring plus friction).
The solenoid must be mounted with the core vertical, so the core moves up.  This
motion must be translated by a linkage into whatever motion you need to do what
you do when you manually disengage decompression.

The linkage on the SR-1 is as follows (motions given for start up--shut down is the opposite):
Solenoid -- electromagnetic pull
Core (moves up) -- clevis pivot to
rod  (moves diagonally up) adjusteable-length clevis to
pivot -- lever (tilts) connected to
shaft (rotates clockwise seen from outside end) passes though housing --  connected to
lever (tilts) -- clevis to
rod (pulls away from head) -- clevis to
decompression lever -- affixed to
shaft -- passes though head cover -- affixed o
pin -- slips off top of
exhaust valve stem
This allows the exaust value spring to close the exaust value when rocker
releases it on the compression stroke so the cylinder can fire.

(It might be possible to replace the linkage from the solenoid core to the deompression
lever with a mechanical cable, but this would change the sroke might change the amount
of mechanical advantage.  But in your situation, it might be worth a try.)

According to the manual start instructions for the SR-1, the engine needs to crank freely
3 to 20 turns  (depending on the ambient temperature and how long the engine has been sitting).
So on startup. you don't want the decompression to release too soon

On the SR-1, a torque spring located on the shaft where it emerges from the side of the housing
pulls against the solenoid.  It is this spring that is responsible for re-engaging decompression.
Since this spring is not adjustable, I disconnected it and added a tension spring attached to
the decompression lever on the head instead.   http://listerengine.com/smf/index.php?topic=8811.0

At shutdown,  the generator spools down and the AC power declines. At some the return spring
can overcome the solenoid,  and the linkage moves back.    This brings the decompression
screw into contact with the edge of the exhaust valve stem.  When the rocker pushes the
exahust valuve open, the smooth end of the decompression screw slips onto the top of the
valve stem, holding ti open.

2. Fuel Solenoid

* Type: pull
* Power: DC
* Voltage: 12-14 VDC
* Duty cycle: continuous (energized whenever engine is running)
* Stroke: ___ inches**
* Force:  ___ foot-lbs (decreases with distance)**
* Mounting bracket: ______**
* Fastener at end(s) of core: _____**

** Measure for your engine and control linkage.

The fuel solenoid is quite different: it is DC powered.  AC and DC solenoids are not
interchangable.  A DC solenoid hoooked up to AC would buzz.  AC solenoids
have a laminated core with a conductive ring around it that creates a second pole
that is 90 degrees out of phase.  This keeps the solenoid close thoughout the AC cycle.

One problem with all solenoids is that they don't force when the core is fully extended. 
So it's a good idea to keep the stroke as short as feasible, and to use mechanical
advantage during the first part of the stroke.   However, the fuel solenoid has to move
the entire rack.

To overcome this, the fuel solenoid on the SR-1 has a "helper coil" that pulls more
power than the main coil.  When he solenoid is first energized, the helper coils
is on, giving an extra pull to core.  After the core moves fully inside the solenoid coil,
it opens a leaf switch, disconnecting the helper coil.

Important: the helper *must* be shut off -- it ir remains on the wire in the coil will
overheat and melt (usually at just one spot).  So you must make sure that nothing
prevents the core from slamming into the switch and opening it.  Fore xample, if
there is a manual override that positions the staring solenoid int he "on" positoin,
the linkage must be adjusted to make sure that the core is fully inserted in the coil
and firmly holding the switch open.

SR-1 START sequence of events:
1. Engine  at rest state:
   * no engine motion
   * decompression engaged
   * rack in shutoff position (all he way to the right)
   * Control lever in START position (i.e, not latched on auto-start models)
   * Relays open, no current flows
2.  Remote or local START switch closes
3. Certain relays close
5. Fuel solenoid: normal and helper coils energize
4. Fuel linkage moves, rack pulled to START position
5. Fuel solenoid ore pushes switch open, shutting off helper coil.  Main coil still energized.
6. Field coil and DC commutator energized: generator unit functions as DC starter motor
7. Engine and generator spool up: 3 to 20 full cycles
8. Decompression solenoid overcomes return spring, linkage moves decompression lever
9. Exhaust valve closes on compression stroke, engine fires
10. Engine and generator come up to full speed as
11. Governor moves rack to the right, decreasing amount of fuel
12. Fuel solenoid linkage to control lever to RUN position
     (= latched on remote-start model).
SR-1 STOP sequence of events:
1. Engine  running: state
   * engine and generator turning over at design RPM
   * decompression disengaged
   * rack under governor control
   * Control lever in RUN position (i.e, latched on auto-start models)
   * Certain relays closed, DC current to fuel solenoid (main coil only)
      and generator stator coil; AC current to decompression solenoid
2.  Remote or local START switch opens
3. Certain relays open
4. Fuel solenoid:de-energized
5. Fuel linkage moved by spring, rack pulled to STOP position, unlatching control lever
6. Firing ceases.
7  Engine and generator spool down
8. Decompress solenoid overcome by return spring, linkage moves
9. Decompression pin in contact with edge of exhaust valve stem
10. Rocker allows exhaust valve to close, decompression pin slips onto top
    of valve holding it closed
11. Engine motion ceases
12. Shutdown state: No AC voltage.  No battery current flows.

Much trial and error will be required to get any non-exact replacement solenoid or improvised
linkage working--but it's quite possible to do.  Good luck!


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Re: LD1 Start-O-Matic solenoid information wanted
« Reply #2 on: October 31, 2019, 07:21:24 AM »
Many thanks for the information, pinecone9. Sorry for the delay in replying but have been away from home.

I have started making up linkages that are missing on my LD1. Once I have those completed, I will be experimenting with a few solenoids.

It looks as though the LD1 and the SR1 SOMs use similar linkages and solenoids so your information is very relevant to my machine except for the generator itself. Mine is a 1.5kW and only has a Lister ID Plate.

Does yours use the same wall mounted control box? I donít have a control box and I intend to fabricate one. I am trying to work out what I am going to use to replace the toroidal choke as it is fairly critical to the correct auto starting system.

Cheers and thanks again.

Alan Hale

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Re: LD1 Start-O-Matic solenoid information wanted
« Reply #3 on: June 01, 2020, 09:33:46 AM »
Hello I have a start o Matic to and need help with getting it working    Alan