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Mechanics Corner: From batteries to starters

Jim Schlund Published on 11 January 2011

In the last column, I discussed batteries because they are the source of the electrical system. In this article we will continue our discussion on electrical systems, shifting focus from the battery to the starter.

The battery cables are directly connected to the starter and the ground. Then you have neutral safety switches and some kind of starter switch, which could either be a key switch or a relay (mag) switch leading into the solenoid starter. These neutral switches prevent you from starting the engine while it is in gear, making it more of a safety switch.

One thing to keep in mind is that starters require a high current to crank the engine. Mag switches and relays are there to keep this high current and amperage off of your key switches and out of the dash panels.

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Some equipment requires close to 1000 amps of current or more to crank the engine when it’s cold. Other applications will require double that amount.

How a starter works
The solenoid is the electric switch on top of the starter. When the solenoid is put into motion, it connects the battery to the starter motor, which is nothing more than a set of opposing magnets. The starter has a conductor, the armature, which is insulated and copper-wound, that runs inside and has magnetic fields around it. They are like two poles or magnets which repel each other.

There are also some iron components in there which intensify the magnetic field. There are also laminations in the armature of steel and copper, creating an electromagnet. Because the two poles oppose each other, they create a motion which will cause the armature to turn.

There are a lot of little things going on at the same time. When you hit the key switch, it wakes up the starter and energizes the solenoid. This in turn, will start to put the starter in motion, just barely.

The energy from the starter motor goes into a starter drive. The starter drive, which is basically a one-way clutch, has to engage into the flywheel at the same time as the armature starts to turn. It is mechanically forced into the flywheel.

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There are two different forces at work here. An electromagnetic force makes the starter work, while the gear drive in the flywheel cranks the engine over mechanically.

Also, keep in mind that the starter has to turn 15 times faster than the flywheel.

Starter problems
There are several ways in which a starter drive can become damaged. When the engine starts, the starter could still be engaged. However, this doesn’t usually hurt the starter or the drive.

You don’t want the starter to be engaging while the engine is running either.

If the engine is going faster than the starter is, it disengages. It freewheels; by then you should be off the key switch. The starter drive serves as a safety device.

Starters have bearings or bushings that get worn from the ignition starting all the time. So, if they get worn, the clearances that are there will disappear and you will have parts that will come into contact with each other, causing friction and generating heat.

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One of the worst things you can do to a starter is to crank it at one time for more than 20 seconds. You have to let it cool back down again. Heat is a bad thing for starters.

Another thing that happens is that the insulation on the starter’s field coils could burn.

Starter brackets could also get loose because the bolts might not be tight.

To conclude, I’d like to briefly talk about the use of ether when starting equipment. Some operators use ether, which inadvertently puts a lot of pressure on the starter.

If you use ether while cranking and the engine rolls back, you could damage the starter. The ether roll-back timing on the engine can cause the ends of the starter cones on the housing to break. Ether can destroy a starter in a heartbeat.

Because ether is so volatile and the ignition is so quick, it can actually occur before the pistons are all the way up. This will drive them back down or put so much pressure on the starter that it could bend shafts, break gears, damage flywheels and break the ends of starters.

You can cause quite a bit of damage to your equipment, not only your starting system, if you use ether starting fluid improperly.

These are just a few examples, but there are other engine-related problems that can affect the starting system as well. PD

Reader Question:
How does the low-sulfur diesel affect these older motors? Does it lubricate well enough? Should we be running a diesel additive?

Answer:
No added problems have been observed by using low-sulfur diesel. However, fuel that is being refined now needs more filtration, so the fuel filter needs to be changed more often than what the manufacturer says.

Additives contain alcohol, which causes water to run through the system. You want to filter that water out. By putting some of the additives in there, it causes water to go through the system.

Thanks to Deloy Baker for submitting this question.

Jim Schlund

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