How to set dwell AND point gap correctly?

[luketrash]

I'm sorting out everything on my car now that it drives down the road. Per my service manual, point gap is 0.024-0.026 and dwell should be 28 degrees.

However, when I have the points set at .025, I get a dwell of about 55 degrees. I understand how dwell and point gaps work, but what I don't understand is how to get the two of them in spec?

My distributor cam doesn't look like it's worn down at all, so I don't know why it's so far out of range.

So someone educate me on how to properly set up the gap + dwell.

Here's a photo I took while the car was idling at about 350 RPM:


//Edit: There is no guarantee that my dwell meter WORKS. I got it in a dollar box with a timing light at an auction.


http://www.whiteboard.net/~luke/54ford_tech/dwell.jpg

[Unkl Ian]

What kind of motor idles at 350 rpm ? http://www.jalopyjournal.com/ubbthreads/images/graemlins/confused.gif


Time for a new meter,if you can find one.

[marq]

If you are running an 8 cylinder that looks right but it would be out for a 6 cylinder motor.Before i got mu Hei i set my points by dwell of 28-32 on a sbc motor most times i got it dead right at 30 degrees but that dont look too far out for 8 cyl..........Marq

[marq]

p.s dont worry about gap only worry about dwell as thats the one that counts.Get dwell right and the gap may not be right anyway but the dwell will set your points right.............Marq..........oh and 350 rpm ? what the f..........k.........

[luketrash]

I've got a 6 cylinder engine (223)

Well, like I said, the meter might not work right http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

The tach said my car was running at 350 RPM..(it was idling really slow, but yeah.. I thought it was bogus too)

Then again, this cheapie meter I have might be made for 12v, but I figured it was fine to use it on 6v, being that it just senses the impulse off the coil and the other end hooks to ground.

I dunno.. I have a 'Cam angle' meter in the garage that doesn't work either http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

[KnuckleBuster]

Here's the dirt on gap and dwell as I know it...

Set your point gap by adjusting the moveable side of the points. Put everything back together and start your engine. Figure out what the dwell is on your guage...then take the cap off and adjust the ENTIRE points setup (move the plate the points attach to if I remember correctly) one way or the other until you get the right dwell.

This takes a lot of patience and trial and error since you have to keep taking it apart and putting it back together again, but it's worth the effort.

[luketrash]

That makes sense. I mean I could always do the PITA method where I put a protractor to use and check between continuity of the breaker points while rotating the engine with a wrench...

I have a Sears engine analyzer, but it's for 12v cars...

You have to clamp it to the car battery and then use a 3rd probe to the ignition coil to test tach and dwell.

In theory, if you could just double the reading, it'd be near spec, but as you can see it came up with a totally different result.

I hooked the analyzer up to a 12v battery and probed the coil, but the readings were all messed up (it must have to be hooked to the same ground plane or something)



http://www.whiteboard.net/~luke/54ford_tech/ignition/dwell.jpg

[squirrel]

if it runs ok with the point gap set to spec, then throw away the flakey test equipment and drive the car!

[luketrash]

Heh, they're 15 dollar 'lifetime warranty' NAPA points, so why not??! http://www.jalopyjournal.com/ubbthreads/images/graemlins/wink.gif

[Unkl Ian]

[ QUOTE ]
...then take the cap off and adjust the ENTIRE points setup (move the plate the points attach to if I remember correctly) one way or the other until you get the right dwell...

[/ QUOTE ]


Dwell angle measures how long the points are closed,
which is a function of the points gap and the shape of the cam.

As you increase the gap,the dwell angle goes down.

With dual point distributors,you can get fancy moving points back and forth.
On a single point distributor,it doesn't work that way.

If it runs decently with the points gap,and initial timing,set correctly,
you need a new meter.

For the average passenger car,points gap,and Dwell angle,can NOT be adjusted independently.

[luketrash]

Unkl Ian: That's what I thought, and thanks for clarifying http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

On my single points distributor, you don't have many options.. You set the gap, and the breaker pivots on one axis only, therefore if dwell is not in spec, then you'll be having to jack up the gap.

She idles and runs well, but my plugs are getting sooty. I'm at the point now where I've got everything set to factory spec (except potentially dwell) So hopefully it's time to finally start messing with the air/fuel ratio.

[Paul]

[ QUOTE ]
Here's the dirt on gap and dwell as I know it...

Set your point gap by adjusting the moveable side of the points. Put everything back together and start your engine. Figure out what the dwell is on your guage...then take the cap off and adjust the ENTIRE points setup (move the plate the points attach to if I remember correctly) one way or the other until you get the right dwell.

This takes a lot of patience and trial and error since you have to keep taking it apart and putting it back together again, but it's worth the effort.


[/ QUOTE ]

this is not adjusting dwell, this is adjusting timing.

the most eficient way to acomplish what you are describing is to loosen the bolt clamping the distributor down and turn the entire distributor.

.................

sounds like your test equipment is suspect.

but, are your points new?

if there is pitting on one point there will be a small buildup on the opposite point making feeler gauge adjustment inacurate.

Paul

[Gr8ballsofir]

I think he meant the bottom plate OF the points...

[Unkl Ian]

[ QUOTE ]
I think he meant the ...

[/ QUOTE ]

If someone can find a web page that details EXACTLY HOW it is possible to
adjust Dwell Angle independent of the points gap,
I would be VERY interested in reading how this is done.

All my schooling,experience,and research,says it can't be done on a single points distributor.

But I am willing to learn something new.



Sorry,no Wive's Tales,Urban Myths,or beer soaked second hand Bench Racing.

[Mart]

Here's my understanding, which embodies most of what's already been said.
The more cylinders you have, the more critical the dwell.
For an eight cylinder engine, the points have to open and close eight times in one rev of the distibruter. So thats eight times in 360 deg of the dizzy. So that's 45 degrees to be closed long enough for enough energy to be built up in the coil, to open with a big enough gap to prevent arcing, and close again ready for the next cycle.
I dont know where it comes from but it would seem the ideal ratio closed to open is 2:1 so the ideal time the points are closed (also known as dwell) is 30 degrees for an eight, giving 15 degrees open per cycle.
On a 4 cyl setting by just the points gap is good enough because the dwell isn't so critical. I spose a 6 is a bit more critical, but carefully set points will get you around. On an eight, though, it's more critical, and ideally if a good dwell meter is available, use it and adjust the points until a dwell of 30 degrees (or whatever is recommended) is achieved. Some distibruters are designed so the points can be adjusted with the engine running specifically so they could be set by dwell. If you dont have a dwell meter, though, set to the recommended gap, and that will get you as close as you can get to the desired dwell without actually measuring it.
Using the dwell meter is just a better way, and should be used when possible.
Mart.

[Paul]

hmm.. how about pulling the shaft out of the distributor and grinding the cam lobes http://www.jalopyjournal.com/ubbthreads/images/graemlins/tongue.gif

gap and dwell=lift and duration.. sorta


Paul

[mikes51]

When my small block ford had points, I used to remove the distributor cap and adjust the point gap with a dwell meter. I set the hold down screw for the points with a little drag, and adjusted the points according to the dwell meter, while turning the motor with the starter. After I put the cap on and actually ran the motor, the dwell stayed the same. I don't know if that was just luck or what.

I switched over to pertronics eventually.

[Flat Ernie]

[ QUOTE ]
Sorry,no Wive's Tales,Urban Myths,or beer soaked second hand Bench Racing.


[/ QUOTE ]

C'mon, Unk, that's all that's been floatin' 'round this place lately! http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif


http://www.jalopyjournal.com/ubbthreads/images/graemlins/cool.gif

PS - You're right!

[willowbilly3]

OK I don't have time to read all this but I am giving my easy version of adjusting dwell on any non GM (they have the window) Best done with the spark plugs out so the engine will spin easier. With the dist cap off attach the dwell meter pos right to the points and of course ground the other. Now either use an accomplis or a remote start button and while cranking the engine you can read the meter and adjust the points to get the proper dwell.
You can do it with the plugs in but the needle bounces a little and you have to eyeball the high and low to determine a median but it is easy to pop the cap and rotor back on and fire it up to double check. If the dwell is right then the points gap should be if your lobes aren't wore off. It really isn't the best idea to use a feeler guage even though most of us do. You can create microscopic damage that causes excessive poits resistance.

[Gr8ballsofir]

UI, I agree with you. the dwell angle is caused by the point gap. In the past whenever I would set my points with a feeler guage the dwell would be usually be off. I would then go back with a dwell meter and fine tune my adjustment. I think that's what KnuckleBuster was trying to say.