Dual Output Coils

Hello,

In my venture to ready my '69 CL350 (two cylinder) for spring, I've
decided to replace the two stock coils. Problem is, I've done a lot of
searching but can't seem to find the answer to a fairly simple
question.

I've been looking at 5 ohm coils to replace the stock ones (which are
also 5 ohms.) Specifically I'm looking here: http://www.dynaonline.com/english/coils.htm.

The CL350 is a two cylinder with two coils, each with one output that
goes to its own cylinder. I'm wondering if the DC7-1 will work with my
setup - as it's only one coil, but with two outputs? In other words,
can a single coil with two outputs replace two separate coils?

Thanks,

Dave

 

On Mar 20, 5:11?am, wrote:
In other words,

Depends on the crankshaft arrangement. The designers of early inline
FOUR cylinder motorcycles found that the dual lead coil was compact
and reduced the number of parts in the ignition system.

The bean counter$ at corporate HQ liked that idea very much, as it
enhanced profit$...

The design only needed two sets of points or two pickup coils to fire
all four cylinders in pairs. #1 and #4 fire at the same time, and #3
and #2 fire simultaneously too.

But this doesn't mean that an I-4 runs like two twin cylinder engines,
extracting power from both pair of cylinders at the same time.

No, the power strokes of each pair of cylinders occur on different
revolutions, 360 degrees apart.

(The first generation of Honda twins had crankshafts that caused the
pistons to rise and fall in pairs and fire 360 crankshaft degrees
apart. Those Type 1 Hondas could have used a dual lead coil with one
set of ignition points.)

In the conventional I-4 arrangement, number #1 cylinder is on the left
side of the engine, and when the #1 piston is nearing top dead on the
compression stroke with both intake and exhaust valves closed, the #4
piston on the right hand side of the engine is rising on the exhaust
stroke with both valves open.

The fresh fuel/air mixture is just beginning to fill the #4
cylinder...

The dual lead coil that fires #1 and #4 fires two sparks
simultaneously, igniting the mixture in #1 and firing a waste spark
into the weak mixture of the #4 cylinder.

Weak mixtures won't ignite, there's no problem with that waste spark
unless a confused home mechanic accidentally hooks up his coil leads
to the wrong cylinders, thinking that both leads on the left side coil
should go to the left side cylinders and both leads from the right
side coil should go to the right side cylinders.

They don't. The engine gets sparks at the wrong time. It fires
cylinders that are full of burnable mixture.

Now, let's look at the crankshaft arrangement in your
CL350.

Your crankshaft is arranged in what is called the 180 degree
configuration. #1 cylinder fires, then #2 cylinder fires 180
crankshaft degrees later.

Then the engine turns a full 540 degrees before the #1 cylinder fires
again.

The #1 cylinder fires perhaps 10 degrees before top dead center at
idle speed. Both the intake and exhaust valves must be closed.

But what is the #2 cylinder doing as the #1 cylinder is rising to
fire?

It's about 10 degrees before bottom dead center, with the exhaust
valve closed, and it has a fresh charge of fuel/air mixture in the
cylinder.

If you have a dual lead coil, the waste spark is going to light that
mixture off.

You would probably never get a twin cylinder with a 180 degree
crankshaft to start with a dual lead coil installed.

I would recommend installing single lead coils as replacements for
your old coils if they don't work any more.

Back in the 1970's it was all the rage to install cheap automobile
coils that we bought from K-Mart for $6.66.

Some bought the 6-volt coils and used a ballast resistor to reduce
current. Others installed the 12-volt coils without a resistor.

So what if the huge coils wouldn't fit under the gas tank? They put
out 35,000 volts and threw inch long sparks in free air.

They made spark plugs last longer, starting was easier, and the tuner
could lean out the idle mixture for better fuel economy because he
could use a wider spark plug gap.

The downside was ignition points life. The extra current passing
through the coil primaries ate up the ignition points rapidly.

My solution was to install electronic devices that
used transistors to handle the main current, and only used the
ignition points as a signalling device to switch the coils on and off.

 

No, It won't work but you could use two of them and just tape off the unused
lead on each coil if there was nothing else available. Why do you want to
change the coils. Are you having starting problems.

JOhn

 

You're either taking the piss or you don't know what you're talking
about. The "2nd" lead[1] on each coil is the return path for the
secondary winding, so you need to earth it if you wish to use a
double-ended coil in place of a single-ended coil. Leaving it open
will result in a big uncontrolled spark external to the coil, at
best, and a fried ignition module at worst.

[1] Both secondary terminals/coil wires on a wasted spark coil are
electrically identical[2].

[2] Of course the current only flows one way so if you care[3], you
might wish to investigate which one is the (+) and which is the (-).

[3] Ford did, which is why my Focus came from the factory with
two different types of single-platinum spark plugs installed rather
than four identical dual-platinum plugs.

 

Rilly? The coil should induce an AC discharge so unless it's
_very_ highly damped it shouldn't matter -- and the plasma in the spark
doesn't care either way.