'77 400 ci vacuum advance and distributor questions
#1
01-11-2019, 07:30 PM
Join Date: Apr 2015
Location: Conway Springs, KS
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'77 400 ci vacuum advance and distributor questions
I must not know how to properly use the search feature on the page. I keep typing in variations of 400 ci timing and get multiple threads from all over the place.
My stock 400 with 77,000 miles needs timed/adjusted. I got a vintage 1981 Craftsman timing light (never used and in box) and scraped off gunk from balancer, found the marks. Cleaned off the edge of my pointer, looked over the balancer and did not note any rubber sticking out or anything janky (to my eyes anyways).
My distributor shaft is stuck, currently performing PB Blaster and engine warmup cycles and then will attempt to break free next week. I talked to an oldtimer at the local auto parts store called Automart in Wellington KS. I was asking him about "recurving" or "inspecting my curve". He said he only had GM stuff and did not have a line on new spring or whatever it is I am supposed to "recurve". I felt like an idiot but need to ask, so then I can learn. I do not want to chase my tail if my advance is not working or this "curve" is incorrect to start with.
I found this thread and it was interesting, anyone have input on this?
Duraspark_distributor_recurve_instructions_index
Duraspark_distributor_recurve_instructions_page-2
If my vacuum advance is shot, I found these part numbers applicable to my 1977 F250 Supercab Camper Special.
D5AZ-12370-A
D7TZ-12370-C
D5TZ-12370-E
If my distributor cannot be "fixed" the following part numbers
D7TZ-12127-P
D7TZ-12127-R
My idea for now is to check my timing as is and I am looking for 18 degrees and then 36 degrees with advance disconnected and port plugged. I do not have a tach to check RPM's, any inexpensive ideas?
I have researched, lots of info out there, some conflicting. I just want to get the truck running well and move on to another project.
Thanks for any and all advice in advance!
My stock 400 with 77,000 miles needs timed/adjusted. I got a vintage 1981 Craftsman timing light (never used and in box) and scraped off gunk from balancer, found the marks. Cleaned off the edge of my pointer, looked over the balancer and did not note any rubber sticking out or anything janky (to my eyes anyways).
My distributor shaft is stuck, currently performing PB Blaster and engine warmup cycles and then will attempt to break free next week. I talked to an oldtimer at the local auto parts store called Automart in Wellington KS. I was asking him about "recurving" or "inspecting my curve". He said he only had GM stuff and did not have a line on new spring or whatever it is I am supposed to "recurve". I felt like an idiot but need to ask, so then I can learn. I do not want to chase my tail if my advance is not working or this "curve" is incorrect to start with.
I found this thread and it was interesting, anyone have input on this?
Duraspark_distributor_recurve_instructions_index
Duraspark_distributor_recurve_instructions_page-2
If my vacuum advance is shot, I found these part numbers applicable to my 1977 F250 Supercab Camper Special.
D5AZ-12370-A
D7TZ-12370-C
D5TZ-12370-E
If my distributor cannot be "fixed" the following part numbers
D7TZ-12127-P
D7TZ-12127-R
My idea for now is to check my timing as is and I am looking for 18 degrees and then 36 degrees with advance disconnected and port plugged. I do not have a tach to check RPM's, any inexpensive ideas?
I have researched, lots of info out there, some conflicting. I just want to get the truck running well and move on to another project.
Thanks for any and all advice in advance!
#2
01-11-2019, 07:40 PM
Join Date: Apr 2015
Location: Conway Springs, KS
Posts: 218
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I just found this, makes sense finally...I think
-----The term "curve" when talking about a distributor is referring to the advance curve. If you look at a graph of engine RPM vs. ignition timing, you'll see that it's not a direct proportion, it's an exponential function (ignition timing is function of engine RPM). Thus the curve. You use different springs in the distributor mechanical advance to control the shape of the curve.----------
-----The term "curve" when talking about a distributor is referring to the advance curve. If you look at a graph of engine RPM vs. ignition timing, you'll see that it's not a direct proportion, it's an exponential function (ignition timing is function of engine RPM). Thus the curve. You use different springs in the distributor mechanical advance to control the shape of the curve.----------
#3
01-11-2019, 09:51 PM
The vac advance is adjusted with a small flat blade screwdriver into the vac hole. The centrifugal is adjustedby changing springs and altering the stop. As I recall there are two notches for centrifugal limit. You remove the shaft and rotate to a different position for use of the other notch.
Doing this without a distributor machine will require a lot of trial and error.
i had a distributor machine back in the day and curved lots of distributors. You typically will limit the range of the centrifugal advance, Spring it so that it is all in by about 3 thousand engine RPM, and then advance the initial timing to achieve the original total. The vac advance will then probably have to be limited, but always remember that the vac advance is an economy device, so don’t let it apply too much advance when the engine is under heard acceleration(low vacuum.). Let it advance as much as possible at cruise vac level.
Hope this helps.
Doing this without a distributor machine will require a lot of trial and error.
i had a distributor machine back in the day and curved lots of distributors. You typically will limit the range of the centrifugal advance, Spring it so that it is all in by about 3 thousand engine RPM, and then advance the initial timing to achieve the original total. The vac advance will then probably have to be limited, but always remember that the vac advance is an economy device, so don’t let it apply too much advance when the engine is under heard acceleration(low vacuum.). Let it advance as much as possible at cruise vac level.
Hope this helps.
#4
01-11-2019, 10:06 PM
Why does it "need" timing now, particularly?
Does it run OK, fuel mileage in line with what it should be? Just trying to clarify. You've got it correct, the basics. Disconnect and plug the vacuum advance port. Check the mechanical ignition advance through the RPM range up to 3000 or so. Make sure it's done advancing all the way. Make sure it advances to where it should, this is important. 36° is about right for V8. This would be without vacuum advance. The initial timing number isn't so important.
If the distributor is stuck, you've got a problem if an adjustment is required anyway. Re-connect the vacuum advance and see that it adds timing on top when engine is revved. This will be an eye-popping number, maybe 45° or more BTDC don't worry about it, there is no load on an engine in neutral. Thing to avoid is a vacuum leak from a dry rotted vacuum diaphragm. You want vacuum advance to work for you, it adds 15 to 25 per cent fuel economy and runs cooler and smoother.
Does it run OK, fuel mileage in line with what it should be? Just trying to clarify. You've got it correct, the basics. Disconnect and plug the vacuum advance port. Check the mechanical ignition advance through the RPM range up to 3000 or so. Make sure it's done advancing all the way. Make sure it advances to where it should, this is important. 36° is about right for V8. This would be without vacuum advance. The initial timing number isn't so important.
If the distributor is stuck, you've got a problem if an adjustment is required anyway. Re-connect the vacuum advance and see that it adds timing on top when engine is revved. This will be an eye-popping number, maybe 45° or more BTDC don't worry about it, there is no load on an engine in neutral. Thing to avoid is a vacuum leak from a dry rotted vacuum diaphragm. You want vacuum advance to work for you, it adds 15 to 25 per cent fuel economy and runs cooler and smoother.
#5
01-11-2019, 10:57 PM
Lead Driver
And stuck is a fact of life with our engines for some reason. First time I'd ever experienced a truly frozen up distributor body was with my 400, and when I brought it up on the forums many years ago, I find I had lots of good company!
You're doing the right thing with the PB Blaster soaking and heat cycles. But you might have to keep doing it longer than you would expect, plus add some more heat in the form of a quick dab of propane torch or so (not too much of course) and some smacking about with metallic objects to put some shock loads into it as well.
And then, ONLY IF YOU'RE LUCKY, will it spin.
Yep, they can be that bad.
If yours responds to just the soaking, consider yourself extremely lucky.
Paul
You're doing the right thing with the PB Blaster soaking and heat cycles. But you might have to keep doing it longer than you would expect, plus add some more heat in the form of a quick dab of propane torch or so (not too much of course) and some smacking about with metallic objects to put some shock loads into it as well.
And then, ONLY IF YOU'RE LUCKY, will it spin.
Yep, they can be that bad.
If yours responds to just the soaking, consider yourself extremely lucky.
Paul
#6
01-11-2019, 11:24 PM
Join Date: Apr 2015
Location: Conway Springs, KS
Posts: 218
Likes: 0
Received 0 Likes
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Why does it "need" timing now, particularly?
Does it run OK, fuel mileage in line with what it should be? Just trying to clarify. You've got it correct, the basics. Disconnect and plug the vacuum advance port. Check the mechanical ignition advance through the RPM range up to 3000 or so. Make sure it's done advancing all the way. Make sure it advances to where it should, this is important. 36° is about right for V8. This would be without vacuum advance. The initial timing number isn't so important.
If the distributor is stuck, you've got a problem if an adjustment is required anyway. Re-connect the vacuum advance and see that it adds timing on top when engine is revved. This will be an eye-popping number, maybe 45° or more BTDC don't worry about it, there is no load on an engine in neutral. Thing to avoid is a vacuum leak from a dry rotted vacuum diaphragm. You want vacuum advance to work for you, it adds 15 to 25 per cent fuel economy and runs cooler and smoother.
Does it run OK, fuel mileage in line with what it should be? Just trying to clarify. You've got it correct, the basics. Disconnect and plug the vacuum advance port. Check the mechanical ignition advance through the RPM range up to 3000 or so. Make sure it's done advancing all the way. Make sure it advances to where it should, this is important. 36° is about right for V8. This would be without vacuum advance. The initial timing number isn't so important.
If the distributor is stuck, you've got a problem if an adjustment is required anyway. Re-connect the vacuum advance and see that it adds timing on top when engine is revved. This will be an eye-popping number, maybe 45° or more BTDC don't worry about it, there is no load on an engine in neutral. Thing to avoid is a vacuum leak from a dry rotted vacuum diaphragm. You want vacuum advance to work for you, it adds 15 to 25 per cent fuel economy and runs cooler and smoother.
I am considering buying the Fuel-O-Vac gauge and use it to check on my carb settings. That will be next after the timing attempt.
#7
01-12-2019, 12:06 AM
Lead Driver
Don't mess with the distributor just go get a rebuilt one from any parts house.
Set your initial timing at whatever it's supposed to be for a starting point. with the vac advanced unhooked rev it up to 2500 o r so and your mechanical should be all in , you should be in the 34-38 range. if you're not advance or retard it by moving the distributor until you are. reconnect the vac advance ( to ported vacuum ) and again at 2500 you should by somewhere from 45-55. your rpm doesn't matter as long as it's over 2500 , all in means it's all in so at 7000 rpm it's still the same.
Take it for a drive and put it under a load and listen for pinging ( detonation ) , if you hear it back off the timing a little. once the pinging is gone if it starts and runs well you're done. don't worry about rechecking your initial it's meaningless.
Set your initial timing at whatever it's supposed to be for a starting point. with the vac advanced unhooked rev it up to 2500 o r so and your mechanical should be all in , you should be in the 34-38 range. if you're not advance or retard it by moving the distributor until you are. reconnect the vac advance ( to ported vacuum ) and again at 2500 you should by somewhere from 45-55. your rpm doesn't matter as long as it's over 2500 , all in means it's all in so at 7000 rpm it's still the same.
Take it for a drive and put it under a load and listen for pinging ( detonation ) , if you hear it back off the timing a little. once the pinging is gone if it starts and runs well you're done. don't worry about rechecking your initial it's meaningless.
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#8
01-12-2019, 08:28 AM
Senior User
If you install a reman distributor and hear a rapid ticking sound when you start it, shut it off and go get another asap. Happened to me and I ignored it took it for a spin went about 3 miles huge backfire and the distributor blew apart on a very dark cold road and had to wait for a tow home. Sucked
#9
01-12-2019, 10:33 AM
Lead Driver
#10
01-12-2019, 10:43 AM
Lead Driver
#11
01-12-2019, 10:50 AM
Senior User
#12
01-12-2019, 11:04 AM
Lead Driver
I'd rather have a reman. it's the same Chinese junk parts in an original base casting rather than a new Chinese one.
Unless you can find an NOS part almost everything we buy these days for old obsolete rigs comes from the same source. nowhere is this more true than with electrical parts. you can pay more but you're probably going to get the same crap at a higher price. just like the " Genuine Delco " HEI parts I just received last week that were made in Taiwan.
most of it is questionable quality but beggars can't be choosers.
Unless you can find an NOS part almost everything we buy these days for old obsolete rigs comes from the same source. nowhere is this more true than with electrical parts. you can pay more but you're probably going to get the same crap at a higher price. just like the " Genuine Delco " HEI parts I just received last week that were made in Taiwan.
most of it is questionable quality but beggars can't be choosers.
#13
01-12-2019, 12:20 PM
#14
01-12-2019, 03:16 PM
I must not know how to properly use the search feature on the page. I keep typing in variations of 400 ci timing and get multiple threads from all over the place.
My stock 400 with 77,000 miles needs timed/adjusted. I got a vintage 1981 Craftsman timing light (never used and in box) and scraped off gunk from balancer, found the marks. Cleaned off the edge of my pointer, looked over the balancer and did not note any rubber sticking out or anything janky (to my eyes anyways).
My distributor shaft is stuck, currently performing PB Blaster and engine warmup cycles and then will attempt to break free next week. I talked to an oldtimer at the local auto parts store called Automart in Wellington KS. I was asking him about "recurving" or "inspecting my curve". He said he only had GM stuff and did not have a line on new spring or whatever it is I am supposed to "recurve". I felt like an idiot but need to ask, so then I can learn. I do not want to chase my tail if my advance is not working or this "curve" is incorrect to start with.
I found this thread and it was interesting, anyone have input on this?
Duraspark_distributor_recurve_instructions_index
Duraspark_distributor_recurve_instructions_page-2
If my vacuum advance is shot, I found these part numbers applicable to my 1977 F250 Supercab Camper Special.
D5AZ-12370-A
D7TZ-12370-C
D5TZ-12370-E
If my distributor cannot be "fixed" the following part numbers:
D7TZ-12127-P (ID tag number D7TE-12127-PA) = 1977/79 F150/350 400 A/T except CA emission ~ D5AZ-12370-A (Motorcraft DD-715)
D7TZ-12127-R (ID tag number D7TE-12127-RA) = 1977 F150/350 400 M/T except CA emission ~ D7TZ-12370-C (Motorcraft DD-782)
My stock 400 with 77,000 miles needs timed/adjusted. I got a vintage 1981 Craftsman timing light (never used and in box) and scraped off gunk from balancer, found the marks. Cleaned off the edge of my pointer, looked over the balancer and did not note any rubber sticking out or anything janky (to my eyes anyways).
My distributor shaft is stuck, currently performing PB Blaster and engine warmup cycles and then will attempt to break free next week. I talked to an oldtimer at the local auto parts store called Automart in Wellington KS. I was asking him about "recurving" or "inspecting my curve". He said he only had GM stuff and did not have a line on new spring or whatever it is I am supposed to "recurve". I felt like an idiot but need to ask, so then I can learn. I do not want to chase my tail if my advance is not working or this "curve" is incorrect to start with.
I found this thread and it was interesting, anyone have input on this?
Duraspark_distributor_recurve_instructions_index
Duraspark_distributor_recurve_instructions_page-2
If my vacuum advance is shot, I found these part numbers applicable to my 1977 F250 Supercab Camper Special.
D5AZ-12370-A
D7TZ-12370-C
D5TZ-12370-E
If my distributor cannot be "fixed" the following part numbers:
D7TZ-12127-P (ID tag number D7TE-12127-PA) = 1977/79 F150/350 400 A/T except CA emission ~ D5AZ-12370-A (Motorcraft DD-715)
D7TZ-12127-R (ID tag number D7TE-12127-RA) = 1977 F150/350 400 M/T except CA emission ~ D7TZ-12370-C (Motorcraft DD-782)
#15
01-12-2019, 03:24 PM
Do yourself a favor before going all Caveman on it.
First, it would probably be best to roll the engine over manually to TDC on the #1 piston on the compression stroke. Not the exhaust stroke. Using a piston stop would be a good plan here too for reasons mentioned previously.
Then scribe a line or sharpy on both the distributor body and block so as to be able to return the base ignition timing very, very close to what it is now, upon reinstallation. Remove the distributor cap and observe the position of the rotor. Mark a line in parallel with the housing. Note that the rotor should be pointing at the #1 terminal position. When the distributor is reinstalled it's tricky sometimes to get the rotor lined back up properly.
But if you mark everything beforehand and re-index to those marks the engine should start right back up without any drama and run fine. If for some reason the engine were to be rolled over by mistake while the distributor is out simply return the #1 piston to TDC on the compression stroke and everything is copacetic again.
First, it would probably be best to roll the engine over manually to TDC on the #1 piston on the compression stroke. Not the exhaust stroke. Using a piston stop would be a good plan here too for reasons mentioned previously.
Then scribe a line or sharpy on both the distributor body and block so as to be able to return the base ignition timing very, very close to what it is now, upon reinstallation. Remove the distributor cap and observe the position of the rotor. Mark a line in parallel with the housing. Note that the rotor should be pointing at the #1 terminal position. When the distributor is reinstalled it's tricky sometimes to get the rotor lined back up properly.
But if you mark everything beforehand and re-index to those marks the engine should start right back up without any drama and run fine. If for some reason the engine were to be rolled over by mistake while the distributor is out simply return the #1 piston to TDC on the compression stroke and everything is copacetic again.