Distributor advance springs

[SpriceyStuff]

Hey guys. I have an issue with my 74 Dart Sport, 77 Slant Six, where it runs great at idle or low RPMs but at high RPMs it develops a spark knock. To mitigate this issue, I’ve plugged the vacuum advance hose and slightly retarded the distributor. This keeps the knock to a minimum and limits it basically to only high RPMs like 65-70 mph (with 3-speed) before I hear the knocking start. My dad has been working on these cars forever and he says he thinks my distributors centrifugal advance weights are stuck in an outward position, or the return springs are broken. So my question to you guys is, is there somewhere I can go to buy that hardware? A new slant six distributor is prohibitively expensive at the moment, so I’d like to simply rebuild mine if I can find the hardware somewhere. Thanks in advance

 

[Darter6]

Summit Racing Mr Gasket #MRG925B spring kit for Mopar. $16.
Common problem. Stuck advance weights.Clean and lube install new springs.Reset timing.Should be good for another 50 years.

 

[krazykuda]

@halifaxhops

 

[GTX JOHN]

Just take apart the distributor and inspect and clean it.

You could very possibly have an engine problem that is causing to
detonation.

But first look at distributor as I will not cost you any money = Just your time.

 

[67Dart273]

You can easily CHECK to see if they are working. First remove the cap and "spring" the rotor CW and it should move CW with "a little" force and then freely spring back. You can check the advance rate and amount with a timing light. If you do not have a "delay" light (one with a knob that shows advance) you"ll have to "degree" the balancer out enough to use a regular lamp. Do you have a 74 manual? if not send me a PM. Otherwise look up the specs for the distributor in the 73 manual, "close enough" and understand that those are published in DISTRIBUTOR degrees which are 1/2 what CRANK degrees are

 

[Mattax]

Agree with above that its easy enough to check for sticking weights.
But your missng possibly some key info.

74 Dart Sport, 77 Slant Six, where it runs great at idle or low RPMs but at high RPMs

A '74 distributor and a '77 distributor may have very different advance curves even when using the same cam.
I don't know that for sure, but its very possible because each year the emissions package was tweaked.
If your going factory, you need to pick the entire package.

high RPMs it develops a spark knock. To mitigate this issue, I’ve plugged the vacuum advance hose and slightly retarded the distributor. This keeps the knock to a minimum and limits it basically to only high RPMs like 65-70 mph (with 3-speed) before I hear the knocking start.

65-70 mph in 3rd gear is just the beginning of what I call high rpm.
The question here is whether its rattling with the gas pedal floored or part throttle cruising/light acceleration.
At WOT or near WOT, then the vac advance is irrelevant anyway.
If the rattling is under cruising throttle/light acceleration then your experperiment has demonstrated too much timing is a combination of vac advance and centrifical advance and initial. I will guess that someone had 'hotrodded' the distributor by removing the secondary spring and/or too much initial for the setup.
Also, on '74 there was a timing delay. Bypass it, if you haven't done so yet. Just take the vac advance hose direct from the carb timed vacuum port to the distributor.

 

[Mattax]

A '74 distributor and a '77 distributor may have very different advance curves even when using the same cam.
I don't know that for sure, but its very possible because each year the emissions package was tweaked.

See the specs @Bugman posted here for '78:Distributor recurve (scroll down to see them plotted).
Notice one distributor application has the the initial timing of 2* ATDC at 750 rpm while most of the others are at 12* BTDC at 700 rpm. Big difference!
Compare those with 1967 non-emissions distributor in a car which was 5*BTDC at 650 rpm.
Big difference again.
We can check what '74 had but the point is that the initial is specific to the distributor because of differences in the advance curve.
So if you are setting the '77 engine for a 12* at 700 and using a distributor intended for 5* or 2* BTDC at 700 rpm, then it will ping and possibly even damage things at WOT.

 

[halifaxhops]

@halifaxhops

I sold them all watch out for the MR G and MP springs they will advance full in at say 1500. They Will make it ping!

 

[SpriceyStuff]

Agree with above that its easy enough to check for sticking weights.
But your missng possibly some key info.

A '74 distributor and a '77 distributor may have very different advance curves even when using the same cam.
I don't know that for sure, but its very possible because each year the emissions package was tweaked.
If your going factory, you need to pick the entire package.

65-70 mph in 3rd gear is just the beginning of what I call high rpm.
The question here is whether its rattling with the gas pedal floored or part throttle cruising/light acceleration.
At WOT or near WOT, then the vac advance is irrelevant anyway.
If the rattling is under cruising throttle/light acceleration then your experperiment has demonstrated too much timing is a combination of vac advance and centrifical advance and initial. I will guess that someone had 'hotrodded' the distributor by removing the secondary spring and/or too much initial for the setup.
Also, on '74 there was a timing delay. Bypass it, if you haven't done so yet. Just take the vac advance hose direct from the carb timed vacuum port to the distributor.

It starts to barely knock right before every upshift, then once I’m in 3rd, it starts to knock on freeway speeds. I’m fortunate that I have alternative routes to work, but at least now I have time to mess with it. On the other hand, I know that the issues was WAY worse before I put a new timing set on it, which I did just a little over a week ago.

 

[SpriceyStuff]

Agree with above that its easy enough to check for sticking weights.
But your missng possibly some key info.

A '74 distributor and a '77 distributor may have very different advance curves even when using the same cam.
I don't know that for sure, but its very possible because each year the emissions package was tweaked.
If your going factory, you need to pick the entire package.

65-70 mph in 3rd gear is just the beginning of what I call high rpm.
The question here is whether its rattling with the gas pedal floored or part throttle cruising/light acceleration.
At WOT or near WOT, then the vac advance is irrelevant anyway.
If the rattling is under cruising throttle/light acceleration then your experperiment has demonstrated too much timing is a combination of vac advance and centrifical advance and initial. I will guess that someone had 'hotrodded' the distributor by removing the secondary spring and/or too much initial for the setup.
Also, on '74 there was a timing delay. Bypass it, if you haven't done so yet. Just take the vac advance hose direct from the carb timed vacuum port to the distributor.

I bypassed the delay, but out of ignorance lol. I didn’t know anything about the vacuum amplifier except that I believed it to be some silly emissions component so I just hooked the hose directly from carb to distributor anyway lol. As far as someone modifying the distributor, maybe? The 77 distributor got damaged and I’m gonna try and fix it. The distributor is from an older slant I had laying around. Don’t know what year, but it’s pre-73 (it’s orange). But my dad drove the car to work for a short period of time about 10 years ago before parking it. He’s a mechanic so he may have done something. But I’ve been talking to him about this so I’d think he’d have said something

 

[RustyRatRod]

Remove the cap taking note of where the rotor is pointing. Take a picture, even. Pull the distributor and tear it down. It's very simple. It's probably gummed up with dirt and grease and the weights are stuck or springs broken like your dad says. He ain't lived his life to learn nuthin. Listen to him. That distributor is really easy to disassemble. Learn it yourself and you'll never be at anyone else's mercy.

 

[Mattax]

It starts to barely knock right before every upshift, then once I’m in 3rd, it starts to knock on freeway speeds. I’m fortunate that I have alternative routes to work, but at least now I have time to mess with it. On the other hand, I know that the issues was WAY worse before I put a new timing set on it, which I did just a little over a week ago.

That is very load sensitive.
My suggestions are:
1 verify the #1 cylinder TDC and the timing mark on the harmonic balancer agree, if you didn't check it at the time.
2. Measure timing vs. rpm to the extent you can. With a timing tape and/or dial back timing light you can cover a greater range but even without those you (we) will have some information work to from.

 

[SpriceyStuff]

That is very load sensitive.
My suggestions are:
1 verify the #1 cylinder TDC and the timing mark on the harmonic balancer agree, if you didn't check it at the time.
2. Measure timing vs. rpm to the extent you can. With a timing tape and/or dial back timing light you can cover a greater range but even without those you (we) will have some information work to from.

I’ll check as soon as I can. I had abother fuel pump failure so I’m gonna have to flush and change the oil before I do anything else cause it’s full of gas

 

[Mattax]

I’ll check as soon as I can. I had abother fuel pump failure so I’m gonna have to flush and change the oil before I do anything else cause it’s full of gas

That sucks.

I bypassed the delay, but out of ignorance lol. I didn’t know anything about the vacuum amplifier except that I believed it to be some silly emissions component so I just hooked the hose directly from carb to distributor anyway lol.

The OSAC is the one system that should be disconnected. It's simply a delay but trades fuel efficiency and performance for slight improvement in emissions during acceleration. Arguabley its also a safety hazard (due to delayed throttle response) but obviously not so much that the lawyers at Chrysler thought it was dangerous.

Some of the emissions stuff actually works pretty well.
If your engine has EGR, depending on the details, having a working EGR will prevent/reduce pinging. There were several ways EGR was implemented, some can be mechanically blocked off. EGR controled properly is shutoff when the engine is cold, and when the throttle is floored or close to floored.

Here's a 318 EGR vacuum diagram someone posted that used a venturi signal. I suspect /6 cars used a different system.

The distributor is from an older slant I had laying around. Don’t know what year, but it’s pre-73 (it’s orange).

Orange overspray? Doesn't help me. I've seen red slants (1960s), and blue slants (70s until).
As fas as pre-73. In general the early (pre-cat) magnetic pickup distributors have to be set with an initial close to TDC, and usually around 700 rpm.

 

[Mattax]

For example, here's the range of acceptable timing advance for a '71 distributor for manual transmission, compared with a '67.

1971 initial is TDC at 750 rpm.
1967 initial is 5* BTDC around 650 rpm.

With good fuel and such, may be able to set the initial a little higher and pick up a little fuel economy. The factory in most cases allowed plus minus 2.5* to account for variations in fiuel, elevation and advance curves at lower or higher end of the spec.

But setting that '71 distributor to have 5* or more at 650 or 750 rpm is likely to result in ping begining around 1600 rpm under any load situation.

Red line illustrates the resultant timing of a '71 distributor installed with 5* initial

 

[SpriceyStuff]

I’m on my break at work right now and I did find this in my basic Haynes manual so I’ll try taking the distributors I have apart when I get back home this evening. This diagram certainly makes it look as easy as Rusty says. Also, based on the valves both being closed when the timing mark is at 0°, everything seems to agree as far as valvetrain timing goes.

 

[SpriceyStuff]

That sucks.


The OSAC is the one system that should be disconnected. It's simply a delay but trades fuel efficiency and performance for slight improvement in emissions during acceleration. Arguabley its also a safety hazard (due to delayed throttle response) but obviously not so much that the lawyers at Chrysler thought it was dangerous.

Some of the emissions stuff actually works pretty well.
If your engine has EGR, depending on the details, having a working EGR will prevent/reduce pinging. There were several ways EGR was implemented, some can be mechanically blocked off. EGR controled properly is shutoff when the engine is cold, and when the throttle is floored or close to floored.

Here's a 318 EGR vacuum diagram someone posted that used a venturi signal. I suspect /6 cars used a different system.
View attachment 1715981655



Orange overspray? Doesn't help me. I've seen red slants (1960s), and blue slants (70s until).
As fas as pre-73. In general the early (pre-cat) magnetic pickup distributors have to be set with an initial close to TDC, and usually around 700 rpm.

No, the block is an older block. It’s orange. But newer parts have been added to it like a blue valve cover and intake manifold, and a blue oil pan. But the block itself is older.

 

[SpriceyStuff]

M

That is very load sensitive.
My suggestions are:
1 verify the #1 cylinder TDC and the timing mark on the harmonic balancer agree, if you didn't check it at the time.
2. Measure timing vs. rpm to the extent you can. With a timing tape and/or dial back timing light you can cover a greater range but even without those you (we) will have some information work to from.

My timing light is one I got from a thrift store for $3 lol so it works but the manual says it’s circa like 1984 or something like that so it’s just a light. No additional features. Will it still work? I’ve marked the timing mark on the balancer with a paint marker to make it much more visible

 

[Mattax]

I’m on my break at work right now and I did find this in my basic Haynes manual so I’ll try taking the distributors I have apart when I get back home this evening. This diagram certainly makes it look as easy as Rusty says.

The snap ring is a royal PIA. The roll pin is a minor PIA until you get experience with them.
Make sure you note which way the reluctor is installed.
Be careful not to use force on the nylon drive gear.

I'd only disassemble one if its hanging up or needs repair.
You can peek though the top plates and see the springs and weights.

This is for smallblock but same idea

Also, based on the valves both being closed when the timing mark is at 0°, everything seems to agree as far as valvetrain timing goes.

both valves closed and the piston at the top, then its fine.

No, the block is an older block. It’s orange. But newer parts have been added to it like a blue valve cover and intake manifold, and a blue oil pan. But the block itself is older.

Well then who knows what it has. You can see here the EGR systems and OSAC in '74. That should help you recognize what does what.
https://mymopar.com/browse-mtsc-by-model-year-1974/
There's no vacuum amplifier for the OSAC, so I think it was for EGR. The EGR valve with no vacuum to it, should block it the exhaust gas - and if so, then the only adjustment to timing needed might be a little less vacuum advance. Bottom line is the exhaust needs to be blocked off.

If there is a snorkel vacuum door(s) make sure it(they) operate or are wired open to outside air...

My timing light is one I got from a thrift store for $3 lol so it works but the manual says it’s circa like 1984 or something like that so it’s just a light. No additional features. Will it still work? I’ve marked the timing mark on the balancer with a paint marker to make it much more visible

If it works, then that and a tachometer will get you started.

 

[SpriceyStuff]

Here’s the springs from the dizzie in the car

 

[SpriceyStuff]

Here’s the springs from the dizzie out of the trunk. This is the one that originally came off the motor in the car

 

[SpriceyStuff]

Welp. I’ve gotten the distributor all the way apart and pried the weights away with my fingers and they snap right back to center. Certainly not the issue. At least, not on the 77 distributor. I talked to my dad again. I discussed with him the information Mattax shared above about the acceptable advance curves. Now I’m beginning to believe that the issue is that the timing was set with a low idle. I’ve only recently adjusted the idle speed. I’m wondering if the reason it didn’t want to run at TDC initial timing was because it was idling too low to begin with. So I advanced it to make it run better, and now since it’s too advanced to begin with it’s far too advanced by the time the weights extend and vacuum advance kicks in. I asked my dad what he thought. He told me it sounded a lot like weights stuck out. I asked if maybe it wasn’t that the weights were stuck out, but rather my own stupidity had led to a specific set of circumstances that together sounded like stuck weights, and he said it’s quite possible. At the time I set the timing, I still wasn’t super familiar with carburetors. At the time I didn’t realize there was an idle adjustment. I just messed with fuel mixture until idle speed came up a bit, but it never was perfect. Probably because the timing was screwed up to begin with, like I said earlier. I don’t have an excuse…

tomorrow my new fuel pump should come in and I’ll get the oil flushed and changed and I can begin experimenting with the car once more. I’ll let you know what happens when I do. Until then, I’m gonna slap this distributor back together and call it a night

 

[Mattax]

I’ve gotten the distributor all the way apart and pried the weights away with my fingers and they snap right back to center. Certainly not the issue. At least, not on the 77 distributor.

Good.
If you want to better understand how the springs and weights work, pry on just the weight attached to the blue secondary spring. It has a long loop, so that spring only engages after the the weights have moved out X number of degrees. The primary spring applies alone applies force from zero rpm until the secondary spring engages. The weights are joined by the slotted plate. This was how Chrysler shaped the advance, providing a quick advance off of idle, then a slower advance.

Now I’m beginning to believe that the issue is that the timing was set with a low idle.

Nope. Initial should always be set at slow idle. Did you read the snips from Chrysler Tech that Bugman posted in the thread I linked earlier?

You can't set initial timing at an rpm where the weights have begun to advance.
Lets use a '67 distributor as an example.
Take your pencil and put it on 5* BTDC but at 1200 rpm instead of 600 rpm.

At 1200 rpm the timing is the initial plus 5* of advance from the weights moving outward.
Timing at all rpms will be late, power and efficiency will be lost. That lost energy will go into the lower cylinder walls and exhaust as heat.

He told me it sounded a lot like weights stuck out. I asked if maybe it wasn’t that the weights were stuck out, but rather my own stupidity had led to a specific set of circumstances that together sounded like stuck weights, and he said it’s quite possible.

Well I don't think its likely. Weights will stick from corrosion or rough surfaces but the springs, in particular the heavy secondary spring has a lot of force to return the weights.

At the time I didn’t realize there was an idle adjustment. I just messed with fuel mixture until idle speed came up a bit, but it never was perfect. Probably because the timing was screwed up to begin with, like I said earlier. I don’t have an excuse…

Timing and fuel mixtures go hand in hand. A factory emisions era carb runs fairly lean idle mixtures - often as lean as 14:1 AFR. This is one reason for the higher idle rpm -it makes up for the lost power.
If you can run it a bit richer, it should be strong and smooth at relatively low rpm. With an automatic, when placed in gear the engine should not lose much rpm if any.

When you adjust fuel mixture, adjust out (CCW) until its smooth, then adjust in (CW) until it drops rpm or vacuum. Adjusting in toward lean the drop off will be more sudden and noticible. Then turn back richer 1/8 to 1/4 turn from when it began to drop off. In gear (under load) it will need richer.

If the idle mix screw is not very responsive when screwed inward, then throttle is probably too far open.

 

[Mattax]

At the time I set the timing, I still wasn’t super familiar with carburetors.

Here's a pretty complete list of Chrysler Tech Manuals
Master Technician Service Conference - Chrysler's Training for Mechanics

If you prefer pdf, or want some of the ones that imperial club doesn't have, you can find most at www.mopar.com
But the descriptive list at the Imperial Club is still useful to know what year and session to look for.

if the reason it didn’t want to run at TDC initial timing was because it was idling too low to begin with. So I advanced it to make it run better, and now since it’s too advanced to begin with it’s far too advanced by the time the weights extend

and that's the scenario I illustrated in here with the red line.

The red line is the 1971 distributor advance (pink) with the initial shifted up from 0* to 5* BTDC.
I drew it in red because its going to ping. It not only sounds bad, but under heavy load it can damage the engine.

RPM, Crank position & Ignition Timing.

 

[SpriceyStuff]

Well, she’s dead boys. I put everything back together yesterday. Flushed the gas-infused oil out and replaced with new oil. Added some power punch like my dad suggested. Started it up and ran it for a few minutes. She’s still knocking and it’s getting louder. It almost sounded like it may have been a pushrod for a bit so I turned it off and pulled the valve cover only to find nothing wrong in the valve train. I don’t know what’s broken at this point, but it’s something bad. So it’s gonna be parked at my brothers house again probably until next spring when I can take some time off work again to work on it. This is a very depressing time for me. I worked hard on this car for months this spring just to park it again so early in the year for the same reason I had to park it 3 years ago. At this time, I’m wondering if I’m going to just need a new engine. Last engine this happened to, the crank was completely destroyed in the rear end. This one is even sadder to me because it’s a cast crank motor, and I had big dreams for the build I was gonna do with it. But I suppose this way I’ll save some money over the winter…