SMTA starting/ignition problems

Wicksfield · May 18, 2014

Got a buddy with a beautiful restored SMTA but it starts hard. We feel it"s an ignition problem. Here"s the symptoms:

1. Ignition on, test light bright on the battery side of the coil and on the distributor side of the coil while holding the points open.

2. When cranking the engine, the test light on the distributor side of the coil is dim and of course flickers when the points open and close.

3. The engine only starts when the starter switch is released and the engine makes one last revolution. That would be the time when the test light becomes bright again on the distributor side of the coil.

Can you guys help us out? Thanks in advance for your response.

El Toro · May 18, 2014

Is there a ballast resistor being used? Check the specific gravity in each battery cell using a hydrometer and post the readings. Hal

Janicholson · May 18, 2014

The issue is voltage to the ignition system while cranking. SMTA tractors need high CCA batteries 800 will do. They also need heavy battery cables because they are long, and the engine is tough to crank, If it is cold out it can draw 550 amps.
The cables need to be 00gauge wire which is about 3/8 of an inch of wire diameter, not including insulation. The connections need to be soldered on and shrink tube sealed to assure tight and high amp conductivity. The ground should connect to the starter motor mounting bolt clean and shiny, then painted if needed.
Welding cable, or OTR truck material is best for construction. Jim

SDE · May 18, 2014

The starter is drawing enough amps away from the ignition system that the engine will not start. My lawn mower was doing that last fall. New battery this spring and it started up very quickly. Told the story to an engineer at work and he told a similar story about his brothers motorcycle. Not enough battery and they will spin the motor, but not start them.
SDE

gene bender · May 18, 2014

Sounds like the wiring has been changed cause you say only starts when sw is released

rvirgil_KS · May 18, 2014

Others have identified the cause being that the starter is drawing down the battery supply so there is low voltage at the coil.

Weak battery or bad connections can be the cause.

One other possibility. Is this 6 or 12 volt system. I've seen a couple of tractors with 12 volt conversion kits give the same problem. The reason was that the supplied resistor for the coil was too high resistance. Should be 1.5 to 2 ohms, on one of mine it was 5+ ohms.

On mine I replaced the 6 volt coil with NAPA IC14SB -12 volt no resistor required- and eliminated the resistor. That cured the problem.

SMTA starting/ignition problems

Wicksfield

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El Toro

Well-known Member

Janicholson

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SDE

Well-known Member

gene bender

Well-known Member

rvirgil_KS

Well-known Member

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