Compression Test & the Starter Motor

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Kansas City MO
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97 ST1100
Hey all,
I tried to run an engine compression test on my '97 ST1100 as per the instructions in the Clymer service manual. According to the book, I should be able to crank the engine with the starter motor while the engine stop switch is OFF. However, my starter motor does nothing without the engine stop switch engaged. Any ideas what I'm doing wrong, here?
 
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The STOP/Run switch electricly completes the running circuit, and likely completes the starting circuit also.
 
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You will have to do the test with the STOP switch in the run position. Make sure all plug wires are away from your hands - the shock can be surprising.
 
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All those plug wires should also be grounded to the engine while turning the engine over.
 

ST Gui

240Robert
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According to the book, I should be able to crank the engine with the starter motor while the engine stop switch is OFF. However, my starter motor does nothing without the engine stop switch engaged. Any ideas what I'm doing wrong, here?
I'm guessing that's an error in the Clymer manual. This was possible in some older Hondas I had.

Honda changed that maybe so that some people wouldn't kill the battery trying to start the bike with the switch inadvertently left in the Off position. I don't know.

I do know I feel a little less stupid when hitting the starter and nothing happens because I made the same mistake. Harder for the casual observer to note my rookie mistake.
 
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I have a 1991 1100. It WILL crank with the kill switch engaged. On the center stand, side stand either up or down...still cranks. With the bike on the side stand, it will not crank regardless of the position of the kill switch.
 
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Not sure what year it changed - my '95 would not crank with the switch off, but early models did allow this. Think I remember reading about it in the old ST1100 Newsletters.
 
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All those plug wires should also be grounded to the engine while turning the engine over.
How about simply unplugging the coil primary wires and insuring they won't touch anything that can ground them?
 
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How about simply unplugging the coil primary wires and insuring they won't touch anything that can ground them?
Sounds like more work to me. Just leave the plugs in the leads and ground the plugs on the engine.
 
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687
:plus1: You need to limit the secondary voltage produced. The ignition module could be damaged otherwise.
OK, I'll preface this by saying I know nothing about coils other than the basic electrical properties involved, but I'd like to understand them better.

The secondary voltage is basically proportional to the primary voltage times the turns ratio, right?

When the primary voltage is switched off (by the ignition module?) the secondary potential is ready to discharge, but if you don't discharge it what happens? Instead of the voltage dropping as the charge is transferred from the coil to the plug, the voltage just stays constant (approximately??) like a battery with no load. This process repeats itself continually as the ignition module turns the primary voltage switch on and off.

So how would the ignition module get damaged? (not a contradiction of your claim, its a question in an attempt to learn)
 
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This was something I learned many years ago, in school auto shop. All these years later, all I remember is there is a possibility of damaging the coils, so I did a quick Google and found this, which also brings up another good reason I had never thought of - risk of fire! This was copied and pasted as is.


"You need to understand something about an ignition coil: When it is time to fire, the voltage going to the spark plug rises very rapidly until it is high enough to jump the gap in the plug. As soon as it jumps the gap, all the energy is dissipated and it is all over till the next time. So what happens if there is no plug gap to jump? The voltage rises to as high as is possible with the system before it stops---OR jumps somewhere else. That somewhere else could be through the side of the coil. Once it arcs through the side of the coil, it is a junk coil.

In some cases, as the voltage collapses, it feeds back through the powerpack. That can cause damage too. I suppose that all depends on the design of the system. Maybe you will get away with it, maybe you won't.

There is another reason for grounding the leads. If they are near a grounded object, they can arc to it. When the motor is cranking, fuel is being pumped out the open plug holes. That, in the presence of the arcing can cause a fire. Believe me, I've been there and done that. Fire shot out about ten feet. Dang lucky I was standing to one side."


Reading that last paragraph makes me think that just leaving the plugs in the leads and grounding the plugs on the engine still leaves a chance that the spark at each plug could ignite those vapours too, so probably best to wire the leads to a ground so there is no spark at all.
 
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"You need to understand something about an ignition coil: When it is time to fire, the voltage going to the spark plug rises very rapidly until it is high enough to jump the gap in the plug. As soon as it jumps the gap, all the energy is dissipated and it is all over till the next time. So what happens if there is no plug gap to jump? The voltage rises to as high as is possible with the system before it stops---OR jumps somewhere else. That somewhere else could be through the side of the coil. Once it arcs through the side of the coil, it is a junk coil.
OK, that makes sense, thanks.
 
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Not sure what year it changed - my '95 would not crank with the switch off, but early models did allow this. Think I remember reading about it in the old ST1100 Newsletters.
True.....my 92 would crank with Stop/Run switch in Stop position and on side or centerstand...twas somewhat embarrassing more than once:rolleyes:.
 
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The coils are connected with one 3 pin connector. Couldn't that connector be unplugged and simply take the coils out of the equation altogether?
That might work, I guess, but isn't that connector buried underneath the air cleaner housing, making it more work to just do a simple compression test?
 
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That might work, I guess, but isn't that connector buried underneath the air cleaner housing, making it more work to just do a simple compression test?
The 3 pin connector is behind the left maintenance cover on the wiring harness that runs along the frame rail at the top end of the maintenance cover opening
 
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