theory of ignition - troubleshooting

[romantic comedy]

Hanley,

Simply put, the condenser stops the points from arcing. It makes the break of current flow nice and clean. It keeps the points from arcing and burning also.

[HalcyonS]

Thanks everyone for useful info and support.
I teach electronics and long ago had old british cars (morris and MG) so the general layout of and old flatop 4 w/carb is not unfamiliar. But I hadn't put my electronics knowledge to work on the subject beyond basic wiring.

Since I'm going to work on it tomorrow, two simple questions are nagging:

1. testing spark. Can't I just pull the lead off the plug and turn the engine over, grounding spark to block? If so, spark gap should be ~ 1/2"? Spark should be bluish as opposed to yellowish?

2. Per Don's suggestion regarding an in-bay ignition switch bypassing wiring harness - where should it run from and to? Not running through a relay, its gotta be a heavy duty switch - is 10A big enough ?

thx
S

[romantic comedy]

Testing spark.

Sure take lead and hold 1/4 inch away from a ground (block). Remember that the rubber cap that fits on the plug will hold the lead away from the ground. Many use a spark plug hooked up to a plug lead, and grounded. Any plug will do. One from an MG too.

Blue is the best spark. Nice and fat if you can get it.

You can also do a quick and dirty test to the coil. Just hook up 12 volts to the positive side. Then hook up a ground wire to the other side. (no other wires are connected) Take the ground wire and touch to ground and off ground. This will cause a spark. Maybe not the best spark, but a quick test.

---------

you just need battery voltage to the coil to run the engine.However you want to do that.

[hanleyclifford]

Yes to both questions. The bypass harness is custom for each boat. The auto stores do sell a handy set up with both ignition bypass and momentary button for starter, or you can cobble your own. You can usually clip on the big starter cable or other convenient live positive. Further to what rc posted; don't be fooled by a spark that is weak and will not jump 1/2". Often a spark will be present but will not be able to fire thru compression.

[hanleyclifford]

Found this interesting discussion: http://www.ratwell.com/mirror/users....r/ketterin.htm

[HalcyonS]

thankyou all, very helpful.
Hanley, that link is nicely explanatory.
S

[Whippet]

MMI videos

Money is dear to us all but a reminder our sponsor sells excellent DVD on ignition systems and video download on timing.

[HalcyonS]

Hold on a minute...

"you just need battery voltage to the coil to run the engine.However you want to do that. "

Surely the starter button does two things - it supplies V to the coil and to the starter motor. Using a bypass switch from, say, starter solenoid to coil will not turn engine so points will not open and close, so no building and collapsing of magnetic field in coil, so no spark voltage... or am I missing something?

BTW - I found this old thread (via google!) on using remote starter

http://www.moyermarine.com/forums/showthread.php?t=6419

[Overdraft]

Hold on a minute...

"you just need battery voltage to the coil to run the engine.However you want to do that. "

Surely the starter button does two things - it supplies V to the coil and to the starter motor. Using a bypass switch from, say, starter solenoid to coil will not turn engine so points will not open and close, so no building and collapsing of magnetic field in coil, so no spark voltage... or am I missing something?

The ignition switch provides V to coil. The starter button provides V (momentarily) to the starter solenoid. The remote starter switch is used to parallel the normal starter button. Note that it controls the starter solenoid: it does not carry the full starter motor current. To check spark: disconnect plug wires (so the engine doesn't start on 3 cylinders). Connect one of them to a spark plug lying on the head. Connect your remote switch from a convenient source of 12V to the starter solenoid. Turn on ignition switch (otherwise no spark as you mentioned). Crank engine to check for spark. Good luck and have fun!

BTW: I think 1/2 inch is too far for the spark to jump. Note the normal plug gap is .035 inch!

[romantic comedy]

Halcyon, it was an answer to a question, about the coil. Not about the engine as a whole.

I agree, 1/4 is best. I wonder if I typed it wrong.

[HalcyonS]

overdraft
thanks for walking me through that - makes perfect sense now

" Note that it controls the starter solenoid: it does not carry the full starter motor current."

that makes sense. As I understood, someone said to connect switch to the main wire coming from battery ie full amps. That didn't seem right.

So just to be clear, bypass switch runs volts from some +ve source, ie battery wire on solenoid, via mom switch to 'start' contact on solenoid? I can easily remind myself which contact that is.

and rc, thanks again
S

[joe_db]

Two wires* go to the solenoid, which is the smaller round thing that is on top of the starter. There is the thick battery cable that goes to the battery switch and starting battery. It is usually someplace between a 4 gauge wire and a 1 gauge wire. The bolt it connects to is large enough to need a 1/2 or 9/16 wrench to loosen the nut that holds the wire on. The other wire is much thinner - somewhere around 10 to 18 gauge - and connects to a much smaller bolt. That wire runs to the starter button or start terminal on the key.

If you get a starter switch from the car parts store it will have 2 alligator clips on the end of the cable. You can connect one to the battery cable terminal and one to the start terminal. When you press the button current flows from the battery cable, through the switch, and back to the start terminal. This current activates the solenoid whcih both moves the starter gear out to connect to the flywheel and makes an electrical connection to the starter motor. Note the starter current is NOT going through your handheld switch, just the 10 amps or so the solenoid needs to make the connection. If the ignition switch is ON the motor shoud start. If it is OFF the motor will turn over and not start.

* note there are two small terminals on the solenoid. The other one supplies power to the ignition coil that bypasses a ballast resistor. 99.9% of A4s do not use this system and it will not have a wire to it. If you do have 2 small wires on your solenoid, you will need to trace them and not connect yout starter switch to the one that goes to the coil. Also note cranking without running will flood some engines unless you turn the cooling water intake off.

overdraft
thanks for walking me through that - makes perfect sense now

" Note that it controls the starter solenoid: it does not carry the full starter motor current."

that makes sense. As I understood, someone said to connect switch to the main wire coming from battery ie full amps. That didn't seem right.

So just to be clear, bypass switch runs volts from some +ve source, ie battery wire on solenoid, via mom switch to 'start' contact on solenoid? I can easily remind myself which contact that is.

and rc, thanks again
S

[hanleyclifford]

Here is a basic wiring diagram that we've had around for awhile: notice the "R" terminal is not used in this picture. As has been noted most A4 applications have not needed that extra starting boost but now with EI and our better understanding of coil voltage problems (and resultant increased use of resistors) I think more and more members will begin to use it. The "R" terminal goes directly to coil+. I have begun to use this circuit with good results. The diagram shows no resistors so it is a bit dated.

[HalcyonS]

Joe, thanks. I rebuilt my starter and solenoid so I know the territory, I wasn't on the boat when I wrote and recalled 3 terminals on the solenoid. I also know about the raw water issue. I *no longer* open it till motor is running.
Hanley, thanks for the diagram and notes. Tomorrow is boat job day!

[HalcyonS]

distributor/coil discoveries

Sooo....

I worked over the entire ignition system. Plugs good. oily, but not sooty. Gaps good. Checked and lubricated distributor centrifugal springs, changed out points, condenser and rotor.

How do you know if a condenser is shot?

Rotor was fairly worn - see comparison pics of old and new ones. You might find them amusing.

The contacts in the cap seem deeply grooved too. (see pic). I have a replacement cap but it seems cheap, with aluminium contacts instead of brass - should I use it?

Tested resistance on coil. 7.1 ohms. Should I worry about this?

The good news is, it started. The bad news is:
1. it suddenly died after 5 min. (Then it ran for 20 min)
2. it won't idle and dies at below 1500 rpm when warm, 1750 when cold.
I'm assuming this is a gap/ timing issue. I set the gap to .018.
An tips of rough and ready timing without a timing light?
thx!
Simon