plaidside

This post will give you a basic explanation of what a typical scope pattern is.
If there is continued interest I will explain more in detail with some examples of bad patterns and what to look for.
Joe


This is the scope I own. It is not the best I have ever used but it is portable and small enough to carry and put on a shelf. It is good enough for
basic testing and diagnosis.


Here are the cable hook-ups. Coil inductive lead, number one trigger inductive and primary negative.


I use this cylinder balance tester in conjunction with the scope, a vacuum gauge and a timing light to check and diagnose an engine. If necessary I would then use a compression gauge and a cylinder leakage tester.


Here is a typical single cylinder scope pattern. This represents 45 degrees of distributor rotation. (45 x 8 = 360)

#1 - Plug firing voltage:

A typical coil can produce approximately 25,000 to 30,000 volts. (25 to 30 KV) This voltage spike tells us how much voltage it takes to overcome all the resistance in the secondary circuit. This includes the coil wire, rotor to distributor segment gap, ignition wire and spark plug gap. It should never take all of the coil’s output to fire any spark plug. Typically it should only take 8-12 KV to overcome all the resistance; the remaining voltage dissipates to ground unused.

#2 - Spark plug firing line:

This is the time the spark is sustained across the gap of the plug. It is usually measured in milliseconds. Typical time is between .8 and 1.5ms.


#3 - Coil/condenser oscillations:

This is the unused voltage that the coil has produced dissipating back and forth through the primary circuit. The remaining voltage in the coil goes to the condenser where it is momentarily stored - first high oscillation (A), then sent back to the coil, second lower oscillation (B), then back to the condenser. This continues until all voltage is dissipated.

#4 - Dwell time:

The sharp downward line (C) on the left is the points closing or the transistor turning on, which starts the current flow in the primary side of the system. This is the start of the build up of the magnetic field in the primary side of the coil. The length of this area is the dwell - how long the points stay closed, or the transistor stays on. Typical V-8 is 30 degrees.
At the far right of the line (D) is where the points open, or the transistor shuts off. This is when the magnetic field in the primary side of the coil collapses over the secondary windings and produces the high voltage needed to fire the spark plug. Notice the thin vertical line at the end of the dwell line (E): this is the secondary voltage spike for the next cylinder in the firing order.

Plasticman

Joe,

Thank you, and please continue with our education.

John (Plasticman)

427Hotrod

Wow....been a long time since I got to play with a scope. Had an Allen Smartscope for years...it was great!

Cool stuff that still works!!

JIM

rwerth7

This is great. When is the next class?

jim lockwood

Thanks, Joe. Post more!

Jim

plaidside

Before the Smart Scope was introduced I was asked to go to one of Allen's centers and "play" with it. I was amazed at the technology.
If I remember it was over $20,000.00 back then.
Didn't it use some type of light pen and think for itself?
I always like Allen machines better than Sun.
Joe

EVERGREEN

Great lesson, thank you.

I have a Glenn's 1967 auto repair manual and on page 41 there is a picture of an Allen oscilloscope/ignition analyzer, also about a dozen pictures of what you can see on the scopes screen for trouble shooting ignition systems.

Thanks again,

Jerry

plaidside

I'm working on it.

rwerth7

Great! I can't wait!

plaidside

I made a change to the hook up picture. I accidently used the one for HEI.:o

Fast Jimmy

Enjoyed it. Keep it up. I have a Sun SS 400 I'd like to learn how to use.

Fast Jimmy

427Hotrod

Yep you're dead on. They were $20K with accessories. About $14K base model it seems like. There was a light pen deal....sort of like an early touch screen. In their day they were state of the art.

JIM

Avispa

You have an MSD box or equivalent lying around? I'd be curious to see the coil secondary voltage pattern on that!

Oh, that "unused voltage" in section 3 is where the voltage in the secondary circuit drops below the voltage necessary to maintain an arc across the plug and the small gap between the rotor and nearest distributor terminal. It builds up first because energy still stored in the coil magnetic field is no longer draining out of the secondary circuit, so it builds up voltage in the primary circuit until you get a spark across the points. When the points spark stops you get to point B.

jtranger

I have the bug to buy a scope. Will this still be advantageous with a pertronix ignition?

jeff mattson

just about any scope should work well on the car you have, its the newer cars that can be troublesome dis cars need special adapters/leads
i own several sun scopes, and ive recently obtained several allen scopes, im waiting on the last box of cables to come in the mail. so i can use the allen smart scope and sea engine analyzer this weekend for the first time.
as far as flexability for testing the allen seem to superceed the sun units i have more test features.
i have alot of bear engine analyzer leads/adapters and boards,software for sale, for bear pace,ace 100-400. for sale
also i have books available for bear/allen repair , and user manuals.
if anyone is interested let me know jeff

kskid

You answered a year old post, in case you did not look at the date.

mike16

I have an Allen Distributor machine.

tried to sell it...

no takers, not even at 150 bucks

C4TOMCAT

Hi Jeff, tried to PM but not getting out to you. I have a Sun 1120 and need a schematic to fix some dials on the machine that are not acting correctly. would you have any info on this machine and any cables and probes that went with it. thanks in advance tom

erb64

how big?

Plasticman

And where are you at? I love playing with equipment like that!

Plasticman