Purpose of starter motor

terencemc

Hi,
Im doing an auto maintenance course and was showed how to bypass the starter motor today?
My question is if you're able to bypass the starter motor and start your car...what is the purpose of the motor?
As it is obviously not just a piece of redundant machined furniture?

Alanstrainor

What do you mean by bypass the starter motor? That doesn't sound right to me, unless you were hand cranking it, i doubt you were starting the car without a starter motor. The starter motor will turnover the engine a few times to start the engine, as a combustion engine can't start without it already turning.

terencemc

Maybe it was a different item but it was certainly bypassing some device... by putting a piece of metal between the "pigtail" and clamp.

colm_mcm

you were bypassing the ignition switch I'd say. any car with an immobiliser won't start without the key anyway.



You need to pay more attention in class

terencemc

Thats the one...I knew it was an ignition switch at the time...just forgot over night !
Yeah the instructor told us to put the key in the ignition and turned on.

Whats the purpose of the ignition switch?
How come it works when bypassed?

colm_mcm

the ignition switch is for switching the car on... it's not exactly practical to jack the car u[ and arse around with the starter motor every time you want to start the car is it?

A bit like saying, "what's the point in having a headlight switch when you could just run a cable from the battery every time you need them?"


Seems a strange thing to be showing people how to do,

terencemc

He just showed us for when the ignition switch was broken.

Rovi

I suspect you were shorting across the terminals on the starter solenoid.
Was it a couple of big threaded connectors (8mm or thereabouts) and you made the connection with a stout piece of metal?

Normally, the keyswitch activates the starter solenoid, which in turn makes the BIG connection to flow current to the starter motor.
What you did was bypass the keyswitch, and flow current directly into the starter motor without activating the starter solenoid.

This is pretty basic 'mechanic' stuff, but not to be undertaken lightly or without understanding what's going on or the consequences of getting it wrong.
You're dealing with re-routing the full power of the battery, (generally) using a bare metal uninsulated conductor, with no fuse or safety cut-out of any sort. Fire is a distinct possibility.

roosterman71

I think you should be asking these questions in class. Remember, there's no such thing as a stupid question

Darragh29

terencemc wrote: »

Thats the one...I knew it was an ignition switch at the time...just forgot over night !
Yeah the instructor told us to put the key in the ignition and turned on.

Whats the purpose of the ignition switch?
How come it works when bypassed?

I think your instructor didn't explain this properly OP. A more accurate statement would to be that the starter motor turns over the engine. It doesn't by itself "start" the engine. A simple example would be that the starter motor cannot start a vehicle that is out of fuel. Even though the starter motor turns over the engine, other events have to happen at the same time for ignition to occur and the engine to actually start, for example fuel has to be metered into the combustion chamber, a spark has to present at the spark plug, etc. In modern engines, these events are managed by the ECU and other functions such as immobilisation algorithims run within the ECU to make sure that the key starting the car has been properly matched with the ECU, etc.

You can "bypass the ignition" and operate the starter motor but if you haven't the other events in place, you won't start the engine.

Robertr

Firstly, I know nothgint about engines etc.. but how does bypassing the ignition switch by hotwiring the starter motor start the car? Does the ingition not have to be on for all the other electrics to work?

colm_mcm

Robertr wrote: »

Firstly, I know nothgint about engines etc.. but how does bypassing the ignition switch by hotwiring the starter motor start the car? Does the ingition not have to be on for all the other electrics to work?

That's correct. the ignition switch would have to be set to the on position, and the immobiliser chip present for it to start


this technique is common on old tractors which don't have ECUs etc.

crosstownk

All of the above is correct. I think your instructor meant "bypass the starter circuit".

The best way to bypass the starter motor is to 'push start'.

L-M

Lots of helpful knowledge on here lads, keep it up

snowman707

Limerick man wrote: »

Lots of helpful knowledge on here lads, keep it up

how's this

make sure it's out of gear, will save you the expense of getting a knee replacement.;)

Delta Kilo

colm_mcm wrote: »

this technique is common on old tractors which don't have ECUs etc.

Many a day I started a tractor in this way. Always scared the hell out of me though. Sparks flying everywhere and you were standing between the front and rear wheels so not much room for escape if she happened to be in gear!

veryangryman

roosterman71 wrote: »

I think you should be asking these questions in class. Remember, there's no such thing as a stupid question

Ugh... "Questions"

Man that girl kept us in an average of an extra hour a week with those stupid questions