setting the gap for the points

[brian3127]

ok let me start off by saying i never set the gap for the points until yesterday.
i was wondering if it was done correctly.
i took the flywheel off. then i noticed that both points were touching until the lobe comes around and opens the gap. The highest point of the lobe is where you set the .020 gap.
i always thought it would be the opposite way as in the lobe would close the gap to .020. Am i thinking to much into it or is that the way it is.
to me i always thought that the points never touch and that the lobe on the cam comes around and closes the gap so that the spark jumps the .020 gap

 

[Chris1956]

Re: setting the gap for the points

You have set it properly. When the points are closed there is a small charging voltage ( a volt or two) in the primary winding of the coil. When the points open the primary winding field collapses, inducing a very high voltage (20K Volts) in the secondary winding, which can jump the spark plug gap. The condenser aborbs some voltage reducing arcing as the points open, and immediately discharges into the primary winding.

 

[OptsyEagle]

Re: setting the gap for the points

The easiest way to think about it is that while they are closed the charge is building up and being stored in the condenser and the micro-second they open it fires down though the secondary coils to the spark plug. The reason for the point gap is to synchronize it to the position of the piston.

By setting the gap you are effectively setting the timing of the spark so that the maximum energy of the spark fires when the cylinder is at top dead center.

If you had set the gap to 0.015" for example, it would put the maximum energy of the spark a little past top dead center. The motor would still run but not as efficiently. Over time as the rub bar (the part of the point that touches the rotating cam) wears down the gap will close a little, hence why tunes up like you are doing should be done every few years or so, if you want the maximum performance from your motor.

The other thing you should do when you are done setting the gap is to dip a clean white business card in laquer thinner and pull is lightly through the gaps to clean any oils or particles from the points. Give them a blow with compressed air. You want them very clean, especially if you are dealing with a failed cylinder. Dirty points is a very common cause.

 

[brian3127]

Re: setting the gap for the points

ok so when the points open does a spark jump across the .020 gap. or get released in a wire to the coils
if it gets release in a wire to the coils why is the .020 gap so important. basicly is a light switch then. no matter how big the gap is its a gap
help me understand i want to learn.

thanks

 

[Scurvy Knave]

Re: setting the gap for the points

the gap spacing is important because it controls the timing (along with the cam roller) and the dwell time that the coil discharge to the plug. There is no sparking across this gap - the condenser's job is to prevent the collapsing charge from jumping the air gap on the points.

The breaker points are basically like a light switch. Their only function is to interrupt the current flow through the primary windings of the coil at the correct time and for the right duration.

 

[kfa4303]

Re: setting the gap for the points

Hi Brian. The points should open to a max of .020" at which point a controlled short is created which then travels down to the spark plug. There is no spark between the points themselves, only in the spark plug, hence the name. Opening and closing the points simply completes, or break the circuit. The points act sort of like alternating castanets. As one pair opens the other closes in an alternating fashion to create the alternate firing pattern of the cylinders. Here's a great link that can walk you through a complete ignition tune up/rebuild.

3 HP Evinrude Lightwin Ignition System Tune-Up 1952-1967

 

[brian3127]

Re: setting the gap for the points

thanks guys that helped alot

 

[HighTrim]

Re: setting the gap for the points

The usual 020 gap measurement of the points is only used to get your points to open at the right time if you dont have a timing fixure to get it right on.Your not actually setting the gap per se, like you are on your spark plugs. You are actually setting the timing. The 020 gap is irrelevant other than that is what it happens to be at, at a certain time (when the rubbing block is aligned with the key), to get the timing correct. If you have a timing fixture, your feeler gauges are not needed.

 

[Boater1010]

Re: setting the gap for the points

The usual 020 gap measurement of the points is only used to get your points to open at the right time if you dont have a timing fixure to get it right on.Your not actually setting the gap per se, like you are on your spark plugs. You are actually setting the timing. The 020 gap is irrelevant other than that is what it happens to be at, at a certain time (when the rubbing block is aligned with the key), to get the timing correct. If you have a timing fixture, your feeler gauges are not needed.

When your setting the points does the throttle need to be wot? or does it not matter.
thanks

 

[kfa4303]

Re: setting the gap for the points

It doesn't really matter. I just put the motor in neutral and the throttle on STOP. All twisting the throttle really does is mechanically rotate the magneto plate to advance the spark, while at the same time opening the butterfly valve on the carb to allow more air/fuel into the combustion chamber. It's more important to make sure that the point gap is set to the highest point on the cam and that they be even. After you remove the flywheel, you can replace the flywheel nut and remove the spark plugs. You can now rotate the crankshaft clockwise using the nut and socket to align the high point on the cam with the points. As the previous posts pointed out a timing fixture is nice, but you don't absolutely have to have one. I've always just use a feeler gauge and it has worked fine for me.

 

[Boater1010]

Re: setting the gap for the points

It doesn't really matter. I just put the motor in neutral and the throttle on STOP. All twisting the throttle really does is mechanically rotate the magneto plate to advance the spark, while at the same time opening the butterfly valve on the carb to allow more air/fuel into the combustion chamber. It's more important to make sure that the point gap is set to the highest point on the cam and that they be even. After you remove the flywheel, you can replace the flywheel nut and remove the spark plugs. You can now rotate the crankshaft clockwise using the nut and socket to align the high point on the cam with the points. As the previous posts pointed out a timing fixture is nice, but you don't absolutely have to have one. I've always just use a feeler gauge and it has worked fine for me.

thanks for the info. Do you by chance know what the resistance should be when testing the ignition coils?
thanks

 

[kfa4303]

Re: setting the gap for the points

I'm not sure right off hand. If the coils are original, then they certainly need to be replaced as they have a 100% failure rate over time. However, if the coils have been replaced, they're probably ok. The replacements are much better quality than the originals and generally last forever unless they have obvious signs of scorching or cracking in the lamination.