repairing/replacing plug wire

This bike is eating me alive ... one mystery after another. Thanks for
all the help so far. I promise to summarize whatever I/we finally
figure out.

1976 Honda CJ360T (inline twin, SOHC, twin points, twin ignition coils
integrated with plug wires)

My left plug wire was showing some damage where the boot joins to the
wire, and I've been having intermittent problems getting spark on that
side, so I decided to replace the terminal and the boot on that side.
The boot is made of hard rubber, which I cracked open with pliers. To
my surprise, I found what looks like an inline resistor inside the boot.
It looks like a ceramic cylinder 5/32" in diameter and 3/4" long with a
little brass cap on each end. My multimeter gives me a reading of
infinite resistance across the device.

I hate to ask whether I can just put on a new boot and crimp a new
terminal onto the end of the wire. I'm sure somebody put that resistor
-like thing in there for a reason.

What should I do now?

 

Assuming you have a multimeter where "infinite" really is a big number,
you should also measure the secondary coil resistance.
I had an open secondary on my VT500C. Went to the motorcycle boneyard
for a replacement. 75% of those were open too. They ran, but not right.
Measure the total resistance of the coil, wire, cap on the good side
and compare that to the bad side.
mike

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Oh, yes, I remember those little resistors in my GT-750 Water Buffalo's
spark plug caps. I think they had about 14,000 ohms resistance. I took
them out and replaced them with brass screws that I'd cut the heads off
of. I couldn't tell any difference... (1)

If you have the type of spark plug that has a nipple that you can
unscrew, you could strip the spark plug wire and wrap it around the
threaded end of the spark plug and screw that aluminum nipple back
down. Lots of engines were built decades ago without that moisture cap
on the plug leads...

Sure. It raises the voltage at which the spark fires across the gap and
it reduces radio static...

Anything you like

Compare the spark coming out of each if the two spark plug leads to see
if they are the same. As I said before, you should have enough voltage
to jump a spark about 1/4 of an inch long when you have a strong
battery and the engine is running. If one spark is weaker than the
other, you can suspect the points, condensor, coil, spark plug lead,
spark plug cap and the 12 volt wiring from ignition switch to coil and
down to the points...

And, don't forget that the points themselves have to be well grounded
to the engine and the engine well grounded to the frame, as in very low
resistance...

(1) Back during the 1970's, everybody was experimenting by replacing
their Japanese ignition coils with K-Mart coils that put out 35KV and
cost only $6.60 apiece. They would jump a spark over an inch long. I
wired my K-Mart coils up with Packard 440 stranded ignition wire. With
all that reserve voltage going to the plugs, I was getting cleaner
running and probabyl better mileage. But my ignition points really
weren't happy with all that current going through them for so long. A
car ignition coil runs through a single set of points with 6 or 8 lobes
and the lobes have what's called a "dwell angle" that you can read off
a dwell rach. With the points opening and closing all the time, they
don't have so much time to heat up.
But a motorcycle ignition cam lobe has just the one high spot that
opens the points. So shade tree tinkerers were fooling around with
firewall resistors and various wire wound resistors to reduce current
through the ignition points. At one time, I had three solid state
switching boxes in heat sinks taking the excess current load off my
points...

 

I was told that it was there to reduce radio signal interference emmisions.
It's like an RFI filter that people used to have to have if there home based
CB radio was causing a neighbor grief. This filtered the radio frequency so
it wouldn't interfere with a television or radio broadcasts.
I would just buy a replacement for a couple of bucks and be done with it.
I'm pretty sure the wire threads on to it.

walt

 

Wouldn't it be a lot easier to adapt the so-called CDI unit from a
CB-750F
16-valve motor to the older ignition points equipped single overhead
cam engines?

Gordon Jennings once wrote that many shade tree tuners believed that
their motorbike engine was so radically tuned, it needed "Gawd's Own
Lightning" to ignite the mixture. And, that just isn't true. The spark
plug will fire whenever voltage rises high enough to jump whatever gap
the plug is set at...

I've ridden dirtbikes with ignitions so weak I could hardly see the
spark in broad daylight. But they ran 70 mph at full throttle with that
spark, so it must have occurred at high enough voltage...

Motorbikes have been built that didn't even have an ignition coil, they
had crystal ignition. Instead of breaker points, one Whizzer moped
engine had a pushrod squeezing a crystal, and every time the crystal
was squeezed, it would make a feeble spark that was enough for the 2 or
3 horsepower engine...

The reason for using high voltage coils in modern automobiles is to
allow the use of a wider spark plug gap with leaner mixtures that don't
pollute the air as much. If the plug gap is 0.050 instead of 0.025
inches, the spark has a greater chance of occurring when ignitable fuel
droplets are passing through the gap...

Motorbikes have been built with distributors and distributor caps. I'm
envisioning an old Harley 45 cubic inch flathead with a distributor
sticking up on the righthand side of the front of the engine...

Distributor caps are exposed to the weather and to damage from minor
tip overs. Another problem is the long length of the ignition wires,
which are also exposed to heat from the engine. Kawasaki had a
distributor on one of their 500cc or 750cc triples around 1969 0r 1970.
I think that model still had ignition points...

Kawasaki's original capacitor discharge ignition system actually did
have the eponymous capacitor that was charged up by a solid state power
supply. You could hear the transistors and inductors and capacitors
inside the box all whining at a very high frequency whenever the
ignition switch was turned ON...

A capacitor discharge ignition sends a high voltage pulse to the
primary of the ignition coil and when the magnetic field in the coil
collapses, voltage rise time at the spark plug gap can be as short as 2
to 7 microseconds. The voltage rises so quickly there just is no time
for much voltage to leak away across the carbon on the porcelain
insulator nose...

Some motorbike tuners who were installing K-Mart coils understood the
business about a critical voltage rise time and that their original
equipment Japanese coils were losing a lot of voltage into that cursed
carbon on their plugs. They were tired of the continual spark plug
cleaning ritual. They said that the high voltage coils had enough
"reserve voltage" to overcome the insulator leakage path problem...

An energy transfer magneto solves the esthetic problem of needing a
battery, while moving the ignition coil closer to the spark plug so it
can have short high tension lead...

My Yamaha DT-1 Single Enduro had an ET magneto. I realized in a moment
of genius that I could improve upon that system by wiring two more low
voltage coils in parallel to the original generating coil. I wound up
with a system that would produce a hot spark at very low RPM, just like
an impulse magneto on a general aviation aircraft...

But I was switching all three coils through one set of ignition points.
I decided that I should have three condensors, too, but there wasn't
room for two more condensors under the permanent magnet rotor. I bolted
the extra condensors to an aluminum clip on the frame of the motorbike.
The clip broke from engine vibration...

That may or may not have been the cause of what happened next. I was
sitting on the starting line of a moto-X race. The engine backfired and
almost stalled, but it was still running roughly when the starter
dropped the green flag. When I released the clutch, my motorbike backed
up ten feet! The 2-stroke engine had been running backwards! It stopped
running when the nut holding the rotor onto the crankshaft loosened up
and the rotor spun off the crankshaft taper...

Modern electronic ignitions that are erroneously called CDI's have a
rather high voltage (up to 500 volts) permanent magnet generator on the
end of the crankshaft to produce the primary voltage needed by the
coil, and the most recent ignition coil designs have placed them right
on the spark plug...

I suppose this may cause coil failure problems due to vibration. One
rider on another list said that Yamaha had problems with this type of
coil on their R6...

There's a lot to know about the electrical engineering that goes into
of motorbike ignition systems, why they are designed the way they are,
and the little disciplines of maintaining them. When they work, they
work fine, for millions and millions of tiny little sparks and when
they don't spark, they are frustrating as hell--- just as Matt is
finding out...

 

Thanks. Okay, I bought new NGK plug caps at a local motorcycle shop for
$4.49 each and installed them. I found that both the new and old ones
screw into the plug cable. I'm sure the bike is the better for it, but
it didn't fix the problem of the left plug not firing. The right one is
going strong.

Before I begin to suspect the coil, can somebody say whether a
misadjustment of the points can cause a complete absence of spark on one
side? I adjusted the points by the book, and I thought I had it right ...

 

If you set your ignition points with too wide a gap (as I recall 0.06
in. is maximum) the points never actually close, so the coil never gets
energized, as it has to ground through the points...

And newbies will make the mistake of setting their points gap on the
low side of the points cam, too...

I used to make beer money tuning up Hondas in parking lots. I would
charge the guys $10 to install a new set of points and set the timing.
I would always gap the points to the maximum gap and the timing would
be a hair advanced.

I did this so when that fiber rubbing block wore a tiny bit, the points
would wear into time, istead of wearing out of time...

My customers said that their Hondas always ran better after I'd worked
on them than they did when too took them to the shop...
------------------------------------------------------------------------
Two young girls bought 1976 Honda 360's and showed up on the boulevard
where us bikers hung out and they started asking questions about their
bikes, typical newbie worrying stuff about things that might go wrong
before they ever did, and I had the points cover off of one of their
bikes and was showing the girls how to set ignition points, and a crowd
of bikers gathered and one silly ass started giving *me* advice about
how to fix the problem...

So, I took the guy aside and asked him if he really was that stupid. He
wondered what I meant by that remark. So I told him that there was
*nothing* wrong with the motorbike, I was just trying to get acquainted
with those two girls who'd secretly gone out and bought motorbikes
without their parents' permission or approval...

He thought that was really strange, trying to meet girls at a biker
hangout so I could get a piece of tail...

Bikers don't do that any more. They don't go to a biker hangout to meet
women and party...

What you see now is a bunch of yuppies meeting at some classic
motorcycle gathering place and talking about their
laptop computers. If they need their motorbike fixed, they call up a
valet towing service and the motorbike gets hauled down to an emporium
where a
white-coated lab tech performs delicate "procedures" upon it and
presents the customer with a bill for half the MSRP of the machine. The
yuppie pays the exorbitant bill and brags to his friends about how big
his repair bills are...

 

Yes, I think it might be the gap, because I changed the left gap shortly
before the problem appeared. I kept the gap in spec though, I believe.
But when I attach a test light to the left points, it does go on and
off as I crank the engine.

I didn't make that mistake, but it wasn't clear exactly where the high
point was. I finally supposed that the range is very big---by that I
mean the high point is not unique. I mean the cam is almost all either
high and low and there isn't much middle ground.

Yes, I think that effect hurt me, especially since the cam was lacking
grease.

<deleted amusing anecdote regarding electronic ignitions' adverse
affects on motorcyclists' dating>

Okay, you guys didn't mention the most practical way to compare the
function of my coils ... I was able to conclude that there is not much
wrong with the previously-suspect left coil.

 

There should be a a distinct opening ramping on the points cam to get a
sudden opening of the points. It wouldn't be good to have the coil's
magnetic field gradually break down as resistance across
every-so-slowly opening points increase. You need those points to break
in microseconds to get the rapid voltage rise time across the plug
gap...

And, why is there only one lobe on the breaker cam? That's to maximize
the saturation time of the small coil's magnetic field...

Figure that your engine can easily turn 11K RPM...

11,000 divided by 2 = 5500 rpm (the cam turns at half speed)
5500 divided by 60 = 91.666 turns per second...
91.666 divided by 2 = 41.83 if the points are open half the cam
rotation...
1 divided by 41.83 = 0.021 seconds to charge the coil to saturation...

 

Okay, I solved it. Somebody guess ... here is the clue: the left plug
would fire when I removed the points cover, but would not fire with the
points cover on.

 

A. Your points cover gasket is missing and the points cover touches the
left hand set of points?

B. Your points cover pinches one of the wires and grounds it?

 

Point wear compensates for cam wear.

 

Points wear when they open and a spark occurs. Not when they "heat up"
while closed. There isn't much current anyway until the instant they're
about to open. And did you tell the tinkerers to do that?

 

Why does it matter whether the gasket is misssing? The cover will be
grounded through the screws anyway. I guess you are thinking that there
is less clearance if the gasket is missing. Anyway my gasket is okay.

Ding, ding, ding!!! krusty kritter nailed it.

There is precious little clearance between the lug for the left-cylinder
wire and the points cover. There was slight interference when
installing the cover, and I noticed a little scratch on the inside of
the cover. There is considerable chance of mistakes when mounting the
points to the round plate. Next time I buy the points assembly, which
includes a new plate, wires, and screws.

Now please tell us how you changed people's points in the parking lot.
With my bike it seems you have to remove the generator cover so you can
see the timing marks, and that implies draining the oil. My owner's
manual mysteriously recommends a dynamic timing check using a timing
light, but it gives no details.

 

Matt wrote:

The Hondas I-4's that I was changing points on had their timing marks
and points right together on the left side of the engine, and the marks
were in a part of the engine that was dry...

There was a "T" mark for "top dead center" and an "F" mark for static
timing, which was around 10 degrees or so before top dead center...

I used a static timing light, which was just a light with two jumper
wires.
When the points opened, the light went out. Another way to time an
engine statically is to hold a small transistor radio near the points.
When they open, you'll hear a static pop on the radio...

 

....and if you're stuck by the side of the road without a
transistor radio or a handy timing light, you can use a
cigarette paper between the points (it falls out when the
points open).

Too bad if you don't smoke.

 

Or you can remove the plug from the socket and ground it and watch or
listen for the spark. If you have a plug wrench o' course.

 

And THIS is a good reason to always have a
victiH^H^H^H^ pillion with you at all times.

"Here hold this and let me know if it's working"
my father taught me this but used a Lawnboy mower
instead of a motorcycle.

8^)
--
Keith Schiffner
RCOS #7
Assistant to the Assistant Undersecretary of the
Ministry of Silly Walks.
"terrorist organization" is a redundancy

 

And the primary circuits are charging concurrently during part of the cycle.