Customs Wht won't my engine start on teststand?

I have an engine that I want to test run on my stand. I wired my test stand and the engine turns over fine....But I have no spark. From my wiring diagram below I wired in the coil (actually tried 2) and have the wire from the dizzy wired to the coil Negative side....The motor turns over great on the test stand but I have NO spark at the spark plug or at the distributor coil wire...Any thoughts

 

well, the diagram looks right, point ignition? if so are the points set right? condenser good? try this, unhook the wire from the coil to dist. unhook at the dist. touch it to ground and look for a spark from the coil. let us know what you find.

 

I'm thinking a bad condenser.

 

the negative terminal on the coil is wired to the distributor, right? it is not in the photo.

 

Understanding how the coil works helps. So when the points are closed, the current runs to ground in the distributer. When the points open the current runs to ground at the spark plug. As stated above, spin the engine with the distributer center wire removed and held close to ground. If there is no spark, then check point gap (dwell) and engine ground.

 

Distributor wire IS hooked to the negative side of the coil......Point gap should not make a difference if I have NO spark at the coil wire BEFORE it goes into the distributor...Correct?

 

points need to open and close. set the gap.

 

It will, point gap will matter if the points don't close or open.

you should look for spark at the high tension wire from the coil, hold it about 1/8 " from ground and ground and un-ground the small primary wire that did go to the dist.

 

For testing purposes you can use a screwdriver to push the points open. You should see a spark at the points when they open and get a spark from the coil (you'll have to hold the lead near ground to see the spark - I'd use some insulated pliers for this or you might get a surprise)

 

The points opening and closing is what causes the coil to trigger a spark, from the coil to the distributor. Point gap and condition, condenser, are critical.

 

just so you can understand, and i will probably not explain it perfect but someone will @squirrel the points need to close to create a magnetic field in the coil, it needs to open just enough to break the field [setting the points] and induce the high energy spark out of the big lead of the coil. this needs to be done at the proper time, when the fuel air mixture has been compressed by the cylinder, so the distributor needs to be in the right place [timing]

 

How much voltage do you have at resistor output? Test w/switch ON. Test while cranking.

 

If you're not familiar with troubleshooting ignition systems, this will give you a good walk-thru of the basics of points type ignitions.

https://www.jalopyjournal.com/forum/threads/hot-rod-technical-library-basic-ignition-systems.983424/

 

Are you getting voltage to the coil? Maybe your switch is bad.

 

Did you ground the motor?

 

This will sound redundant, but I did it to myself once. See if you installed the rotor in the distributor. Leaving it out makes them real hard to start!

 

I had a similar problem about 2 years ago with my flathead engine on a stand and it turned out I had an HEI dizzy but was using the wrong coil.
I took a photo of all my components and somebody here on the HAMB spotted the problem.
Pic's do help...

 

Ask a question then get pissed off when the guys give you the right answer, way to go.
The guys are correct. The points control the coil and the coil doesn't work without the points or an electronic replacement for them triggering it. The points have to open and close and the gap has to be pretty close to right for it to work.

Point gap needs to be set at about .016 with the rubbing block on the arm at the high point of one of the cam lobes in the distributor. That gives the coil time to build up the proper magnetic field when the points are closed.

My thought is that you don't have the points adjusted correctly or you have a wire or connection in the wrong spot inside the distributor.
One other thing and it sounds a bit crazy but I have seen it and that is that someone forgot to put the rotor in the distributor in the haste to get things together.

 

If the points are closed you will not have any voltage at the neg. side of the coil.

What engine is it?

 

aint got no gas

 

I 2nd the rotor...

 

When did it last run and what did you do to it since?

 

Or the distributor gear pin sheared and the rotor is not moving? I know it's a long shot.

 

No,

 

SOME ANSWERS Got voltage to coil........Motor is grounded from neg battery cable.....no nothing about the motor, bought with a project,great compression and oil pressure ...rotor is there and turning...don't need gas for spark....272 Y block...gonna try new rotor and new condensor and point gap next.

 

before you start replacing parts, take a close look at the points. The gap between the contacts should be about .016" when the points are open, and there should be no gap when they are closed. you have to turn the engine and watch them, to see what happens. If they are really dirty, or fried, or are not opening, then you kind of need to change or clean or adjust them.

 

If the engine sat for a long time the points could have a coating on the them, like corrosion. Use an ohm meter and make POSITIVE they are making contact when closed. Don't just look at it and THINK they are touching. If not they will never spark when opened.

 

What’s your battery voltage ?
Using a DVOM what voltage at the + coil when cranking?
Point gap set correctly?
Condenser ok and working ?

Rotor means nothing at this point if you have no spark coming from the coil wire.

Take the cap off the distributor and watch if the points are opening and closing.


Old dirty points? New? Clean FLAT contacts?

Try opening and closing the points with the coil wire grounded, spark plug in the end, screwdriver, finger ( just wait for the WAM !)

After trying all this get back to us with what you find.
Remember a fully charged battery is at least 12.2/ 12.3 volts anything less is discharges.


Start from the very beginning and work you way back. All this should be done by the time the pizza shows up at your door !

 

If you check the points and they are opening and closing, borrow a nail file or Emery board from the wife and run it between the contact areas of the points. Even a small piece of folded over fine grain sandpaper will do. Sometimes points get corroded from sitting for years in the open position...a simple cleanup of the points is quick and free.

 

The key to the entire system is the points provide a ground to the coil -when they are closed and the ground breaks when they are open.

That's where it all starts and ends, it's the first thing to check.