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Setting dwell on a 351
#1
runninpony 
I own a 1972 with a 351c 2-v V8. Dwell angle now is at 44.7. According to my spec sheet needs to be 24-29. Been trying to turn the distributor. Been battling 40 years of rust. Tried spraying liquid wrench and then used an oil filter wrench. I am able to loosen the lock down bolt but no luck with distributor. Any tips,tricks or tools I can use to loosen this up?
  Reply
#2
you don't need to turn the distributor to set Dwell.

Dwell is the duration of electrical voltage that is allowed to come out of the coil and travel to the plug that is firing.

Setting the Timing of when the voltage is sent to the plug requires turning the distributor body.
setting the length of time over which the voltage is sent is dwell.

what dwell means is as the distributor turns a cam inside turns and opens and closes a metal switch, if the plates for the switch are very close together then the switch holds on allowing voltage to pass from the coil to the plug longer. if the plates are further apart then the duration that the switch is on is much shorter. sometimes dwell is called Air Gap. or Dwell angle. the angle refers to how many degrees in a circle the switch is held on or off.

If you have points then you have to deal with dwell.

there is also double points distributors that were designed for higher RPM operation. Points are a big problem at high rpms because the points can bounce and the dwell angle completely thrown out of wack causing major misfires. double points is the most difficult to setup to have to sort of average the dwell angle between both sets of points.

If you have an electronic ignition there is no Dwell angle to set because the switch is no longer mechanical it works off electronics.

ok so in every other distributor setting the dwell angle is external and simple and you can even do it with the engine running.

Some body at ford was busy doing cocaine instead of following what everyone else was doing.

for a ford you have to pop the cap off the distributor, best to disconnect the coil wire as well.
hook up a remote starter and setup your dwell meter.

you loosen the points screws and sit there with a flat head screw driver as you turn the motor over with the remote starter. DO NOT START THE MOTOR you just need to kick the motor over to turn the distributor, and keep it short enough you do not flood the motor.

then as you kick the starter over you read your dwell meter every time the cam kicks the mechanical switch on and off you get your currect dwell reading. you aim for the smaller number in the dwell spec because as the switch wears down the length increases because the air gap becomes smaller and smaller over time. using the screw driver you ever so slightly move the points plate in or out to set the air gap for the switch. a starting point is to use the thickness of a matchbook paper to start at a reasonable air gap.

as dwell wears the engine timing can change as well.

after kicking the motor over and getting the dwell as close to spec as you can you lock the points plate down, reinstall the cap and connect the coil and start the motor up.
double check the dwell, and make sure the plate did not shift as you tightened the points plate.

Repeat at nausea until you get fed up with it and install a petronixs ignitor system or mallory or accel ignition system.

Most of the made in china points wear so fast that you have to keep adjusting Dwell every 1500 miles. if the dwell angle becomes too long from wear, first your engine timing will change and second the coil will overheat and blow out.

now if you want to change engine timing then you need to rotate the distributor itself.


as for unsticking the distributor, do NOT use HEAT! there is a rubber o-ring and also you can ruin the distributor keep using penetrating oil, you can try knocking the engine over with a remote starter it may kick the distributor loose wth the hold plate loose.
you can try twisting the distributor left or right until that o-ring lets go from a combination of penetrating oil and force, i had a hell of a time when i also first worked on my engine i kept hitting it with oil for over a month until one day it finally gave and came loose.
  Reply
#3
72HCODE;85092 Wrote:you don't need to turn the distributor to set Dwell.

Dwell is the duration of electrical voltage that is allowed to come out of the coil and travel to the plug that is firing.

Setting the Timing of when the voltage is sent to the plug requires turning the distributor body.
setting the length of time over which the voltage is sent is dwell.

what dwell means is as the distributor turns a cam inside turns and opens and closes a metal switch, if the plates for the switch are very close together then the switch holds on allowing voltage to pass from the coil to the plug longer. if the plates are further apart then the duration that the switch is on is much shorter. sometimes dwell is called Air Gap. or Dwell angle. the angle refers to how many degrees in a circle the switch is held on or off.

If you have points then you have to deal with dwell.

there is also double points distributors that were designed for higher RPM operation. Points are a big problem at high rpms because the points can bounce and the dwell angle completely thrown out of wack causing major misfires. double points is the most difficult to setup to have to sort of average the dwell angle between both sets of points.

If you have an electronic ignition there is no Dwell angle to set because the switch is no longer mechanical it works off electronics.

ok so in every other distributor setting the dwell angle is external and simple and you can even do it with the engine running.

Some body at ford was busy doing cocaine instead of following what everyone else was doing.

for a ford you have to pop the cap off the distributor, best to disconnect the coil wire as well.
hook up a remote starter and setup your dwell meter.

you loosen the points screws and sit there with a flat head screw driver as you turn the motor over with the remote starter. DO NOT START THE MOTOR you just need to kick the motor over to turn the distributor, and keep it short enough you do not flood the motor.

then as you kick the starter over you read your dwell meter every time the cam kicks the mechanical switch on and off you get your currect dwell reading. you aim for the smaller number in the dwell spec because as the switch wears down the length increases because the air gap becomes smaller and smaller over time. using the screw driver you ever so slightly move the points plate in or out to set the air gap for the switch. a starting point is to use the thickness of a matchbook paper to start at a reasonable air gap.

as dwell wears the engine timing can change as well.

after kicking the motor over and getting the dwell as close to spec as you can you lock the points plate down, reinstall the cap and connect the coil and start the motor up.
double check the dwell, and make sure the plate did not shift as you tightened the points plate.

Repeat at nausea until you get fed up with it and install a petronixs ignitor system or mallory or accel ignition system.

Most of the made in china points wear so fast that you have to keep adjusting Dwell every 1500 miles. if the dwell angle becomes too long from wear, first your engine timing will change and second the coil will overheat and blow out.

now if you want to change engine timing then you need to rotate the distributor itself.


as for unsticking the distributor, do NOT use HEAT! there is a rubber o-ring and also you can ruin the distributor keep using penetrating oil, you can try knocking the engine over with a remote starter it may kick the distributor loose wth the hold plate loose.
you can try twisting the distributor left or right until that o-ring lets go from a combination of penetrating oil and force, i had a hell of a time when i also first worked on my engine i kept hitting it with oil for over a month until one day it finally gave and came loose.

Thanks for the info 72. Will follow your advice as soon as my brother-in-law stops by with his remote starter. Hope I can pick your brain in the future.
CC
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#4
I can recall setting dwell on old cars with a match book cover in the middle of a parking lot just to get it to run. Since smoking is no longer as popular as it used to be, it may be more difficult to find a book of matches laying around than it used to be. Typically, I used (and still do) feeler gauge .018 at the points air gap. Socket wrench on crank damper bolt, by hand - turn engine over until lobe pushes points apart at the max - set gap to .018 (somewhat tight). Start engine and check with dwell meter. Repeat as necessary.

But I also converted to Pertronix years ago and have not done a mechanical setting for some time. However, I do carry my points assembly (with the proper screws) and a matchbook in a ziplok baggie in the glove compartment. I've had two Pertronix set-ups fail in the past 16 years and I was happy to have the necessary parts to get things running well enough to get home.
  Reply
#5
Chicago Chet;85089 Wrote:I own a 1972 with a 351c 2-v V8. Dwell angle now is at 44.7. According to my spec sheet needs to be 24-29. Been trying to turn the distributor. Been battling 40 years of rust. Tried spraying liquid wrench and then used an oil filter wrench. I am able to loosen the lock down bolt but no luck with distributor. Any tips,tricks or tools I can use to loosen this up?

Welcome to the site, Chet. When you get a chance, post up a short intro in the Introductions thread so we can give you a proper welcome.

Doc

[Image: 6y14ea.jpg]

Project started 8-7-10
Completed: All new suspension, rebuilt 351C H Code bored .030 over with mild cam and intake, new 3.50 TracLok, custom exhaust system
Current "mini-project": interior upgrade Undecided
  Reply
#6
Chicago Chet;85089 Wrote:I own a 1972 with a 351c 2-v V8. Dwell angle now is at 44.7. According to my spec sheet needs to be 24-29. Been trying to turn the distributor. Been battling 40 years of rust. Tried spraying liquid wrench and then used an oil filter wrench. I am able to loosen the lock down bolt but no luck with distributor. Any tips,tricks or tools I can use to loosen this up?

Things to remember:

1. To decrease the dwell you increase the gap and vise-versa

2. For every degree you change the dwell you change the timing 2 degree's

So if you change the dwell you may have to reset the timing also!

1973 Mach 1 429 cu. in. H.P. TBD, C6 Reverse Manual Valve with 3500 Stall Tranny, 9" rear 3.90 PosiTrac
2007 Mustang GT Convertible Premium
  Reply
#7
And dwell will change over a period of time. The gap gets smaller so dwell increases. This messes with your timing.

If you are just trying to get it running mess with it but eventually upgrade to electronic.

Welcome to the Forum!

'Mike'
73 Convertible - 351C/4V CC heads/4bolt/forged flat tops/comp 270/rhodes/mallory unilite/tri-power/hookers/glasspacks/c6/3.50 limited slip/Gear Vendors/Global West sub frames, strut rods and shelby style traction bars/ Rear sway bar/tilt steering (not original)

Pics of modifications included in:
  Reply
#8
the best way to loosen the bolt is spray some aerokroil on it,mine got stuck,and i tried everything and this worked the best,you can buy it from amazon......

DRIVE IT LIKE YOU STOLE IT*****KEEP YOUR FOOT ON THE PEDAL

Ron

1972 mustang convertible
2005 mustang convertible
1999 mustang convertible white (sold)
1994 mustang convertible white (sold)
2008 ford edge copper
2006 cadillac cts radaint bronze
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