Why are my distributor cap terminals burnt?

[Mattax]

One thing I did learn was that I don’t think the FBO plate will work with my distributor. .

Good . Saved you from doing this

The plan was to install the limiting plate to keep me around 36-38, but this damn distributor won’t work

I dialed back the initial to 14, and the car sounds and drives SO much better. I can’t remember why I set it to 22 in the first place.

No idea either.

We went over this a while back. Maybe it got lost in the jumble as you ended up with a mechanical issue IIRC.
Something around 13 to 16 * BTC at 600 or 650 RPM.

Remember this graph of the timing with RPM?
This is basically what a factory hi performance 440 wants at full load.
45* at 3400 isn't even close.

On the other hand 22* might have been close IF it was idling at 1200 RPM.

Do you follow?

Do you see that once the advance starts to move, the timing measured is no longer the initial.
Its now initial plus some advance.

The good part about the Mallory type advances is that you can pretty easily adjust them.
The uh challenge with the Mallory type advance mechanism is getting a curve that looks anything like the factory curves.

Before getting into adjusting, measure what it has now.
You have to know where it is now so you can at least guess at what changes should be made.

Get timing vs. rpm at the slowest rpm it will run, then every 200 or 250 or 500 rpm, measure timing again.
Leave the golf tee in the vac advance hose for all of this.
Only after you have the mechanical timing pretty ballpark is it ready for vacuum advance

 

[Mattax]

mallory_instructions_yh_series_mechanical_advance_kit_29014.pdf (holley.com)

Just remember the graph is misleading.
Change the max degrees of advance and the whole curve shifts left.

 

[TT5.9mag]

I agree that phasing CAN be a problem but don't see it here......looks to me like the "most" of the arc is right in the middle area of the contacts.


Also just for clarity, it is not mechanical advance which causes phasing problems, but vacuum advance. The rotor and the trigger device are locked together

yea looking back at his photo you’re correct. The arcing is fairly well centered on the pins in the cap.

 

[Righty Tighty]

Moisture and aluminum terminals. I know Az you live in. Wash the engine in a year? Mopar a long time ago said to put dielectic on the rotor tip, thats right folks lube te tip

You have the Malloty style and well sought after distributor. The hex screws can be loosened and then adjust the mechanical adnvance. The tabs are there for mechanical advance adjstment. Buy a set of keys. Hope it helps.
Hoppy

Oh geez, I just remembered my distributor came with a set of keys. I should use them.

We went over this a while back. Maybe it got lost in the jumble as you ended up with a mechanical issue IIRC.

I think you're right -- I had the heads rebuilt and I think I was excited to get it running again, I forgot about the advice you gave regarding timing. Sorry about that.

On the other hand 22* might have been close IF it was idling at 1200 RPM.

No sir, it was idling around 750...

Do you see that once the advance starts to move, the timing measured is no longer the initial.
Its now initial plus some advance.

The good part about the Mallory type advances is that you can pretty easily adjust them.
The uh challenge with the Mallory type advance mechanism is getting a curve that looks anything like the factory curves.

Before getting into adjusting, measure what it has now.
You have to know where it is now so you can at least guess at what changes should be made.

Get timing vs. rpm at the slowest rpm it will run, then every 200 or 250 or 500 rpm, measure timing again.
Leave the golf tee in the vac advance hose for all of this.
Only after you have the mechanical timing pretty ballpark is it ready for vacuum advance

I need to slow down and pay a little more attention to detail, and be a little more methodical. Then, maybe I won't end up missing steps or forgetting information I've been given.

 

[Mattax]

it's OK. It's normal especially when at the time it you determined the main issues were mechanical.

So lets see what you have and I'll try to help you make the changes in the right direction.
Do remember what springs were in it?
We can estimate from 45-22=23* that may be the advance limit. That looks about right from the photo. Or if you have the distributor apart, measure it with the keys.
Finally, is the engine hot rodded at all and if so what duration and compression?

 

[Righty Tighty]

The springs that are currently in it are blue springs, but the distributor came with heavier and lighter springs, along with charts that show the curve if I used various combinations. The instructions stated that the distributor has mechanical advance of 22-24 degrees.

Unfortunately, I didn't build the engine and the guy I bought the car from didn't have much documentation regarding the components. I measured lift when I sent the heads in so that they could order the correct springs, and if I recall correctly, the lift was .447, although I didn't measure duration. I remember being surprised by the lift, since I was expecting a little more. So to answer your question, I don't think the engine has been hot rodded much.

 

[Mattax]

OK. That helps. Do your instructions have a plot for two blue? Because mine do not. Nor have I run those on the car or a machine.
I think even without, we can make a pretty good guess as to what its doing just based on the spring rates and lengths (which I have).

 

[Righty Tighty]

Awesome, I will check the instructions tomorrow when I’m home from work and report back.

 

[MOPAROFFICIAL]

I see nothing out of the ordinary with the caps terminals.

.035 is fine for stock ignition box.
.045 is fine for msd ignition box.

 

[Mattax]

23 - 24* advance is probably correct as your measured advance seem to to agree with the instructions.
The advance stopping at 3400 rpm would be great. I kindof don't beleive it. But maybe the blue springs you have are different than the ones I got. I would have expected a quicker advance. Either way with two equal springs it is a fairly straight line. If anything it starts a little slow and then rises faster. Thats due to the mechanism's design, not the springs.

Before: Initial of 22* at 750 rpm, Timing using 2 blue springs, limited to 24* advance.

I dialed back the initial to 14, and the car sounds and drives SO much better.

Same as above but initial of 14* at 750 rpm.
The timing is probably in this range now.

38* at 3400 is not out of line for a iron headed big block. Yes the factory curve is more conservative. They had to cover all situations including pulling loads up steep mountains and things like that.
38* at 2600 rpm I think may be a problem when vacuum advance is connected. Its going to add up to a little more timing than it will really like in that rpm range. There's a reason that the factory slowed the advance above 1400 rpm. It wasn't needed or wanted. The engine gets more efficient and the flame grows faster from those rpms up.

Anyway. I'd leave the advance limit at its present setting. If you change it changes the spring tensions and I don't see the need at this point.
If your spring kit has some heavier springs with longer loops, you could try replacing one of the blue springs with a one of the longer looped springs.

Longer looped spring are the bottom row.

Goal is for the spring to have just a little bit of slack with the weights at rest (all the way in).
This spring should do nothing until the weights have moved out a few degrees. It creates the second stage of a shaped advance.
However this leaves just one spring responsible for holding the weights from moving outward at idle rpm.
I'm not sure a single blue spring will have enough tension to do that. If the weights move outward at say 600 rpm, then the timing around 750 rpm will not be the initial - it will be intial plus a several degrees advance.
So if using a long looped secondary spring, probably will need to combine that with a stronger primary spring. Assuming its the same Mallory springs as I've bought, I'd try Brown.

 

[Mattax]

Like this, but less slack on the secondary spring.

 

[Righty Tighty]

I see nothing out of the ordinary with the caps terminals.

.035 is fine for stock ignition box.
.045 is fine for msd ignition box.

Thanks. I'm still new to this, and I don't remember the terminals looking like that when I removed the old distributor on this, or on the Scamp. So I thought something was wrong.

23 - 24* advance is probably correct as your measured advance seem to to agree with the instructions.
The advance stopping at 3400 rpm would be great. I kindof don't beleive it. But maybe the blue springs you have are different than the ones I got. I would have expected a quicker advance. Either way with two equal springs it is a fairly straight line. If anything it starts a little slow and then rises faster. Thats due to the mechanism's design, not the springs.

Before: Initial of 22* at 750 rpm, Timing using 2 blue springs, limited to 24* advance.
View attachment 1715854817



Same as above but initial of 14* at 750 rpm.
The timing is probably in this range now.
View attachment 1715854818

38* at 3400 is not out of line for a iron headed big block. Yes the factory curve is more conservative. They had to cover all situations including pulling loads up steep mountains and things like that.
38* at 2600 rpm I think may be a problem when vacuum advance is connected. Its going to add up to a little more timing than it will really like in that rpm range. There's a reason that the factory slowed the advance above 1400 rpm. It wasn't needed or wanted. The engine gets more efficient and the flame grows faster from those rpms up.

Anyway. I'd leave the advance limit at its present setting. If you change it changes the spring tensions and I don't see the need at this point.
If your spring kit has some heavier springs with longer loops, you could try replacing one of the blue springs with a one of the longer looped springs.

Longer looped spring are the bottom row.
View attachment 1715854819
Goal is for the spring to have just a little bit of slack with the weights at rest (all the way in).
This spring should do nothing until the weights have moved out a few degrees. It creates the second stage of a shaped advance.
However this leaves just one spring responsible for holding the weights from moving outward at idle rpm.
I'm not sure a single blue spring will have enough tension to do that. If the weights move outward at say 600 rpm, then the timing around 750 rpm will not be the initial - it will be intial plus a several degrees advance.
So if using a long looped secondary spring, probably will need to combine that with a stronger primary spring. Assuming its the same Mallory springs as I've bought, I'd try Brown.

The first graph really helps to put into perspective how off my first setting of 22 degrees initial was, so thanks for that. It was a long night at work and it's bedtime, but I'll dig up the graphs and see what they have to say about two blue springs after I'm rested.

 

[MOPAROFFICIAL]

Remember the hotter spark from a hotter coil and perf ign. box fires through that cap.

 

[Righty Tighty]

23 - 24* advance is probably correct as your measured advance seem to to agree with the instructions.
The advance stopping at 3400 rpm would be great. I kindof don't beleive it. But maybe the blue springs you have are different than the ones I got. I would have expected a quicker advance. Either way with two equal springs it is a fairly straight line. If anything it starts a little slow and then rises faster. Thats due to the mechanism's design, not the springs.

Before: Initial of 22* at 750 rpm, Timing using 2 blue springs, limited to 24* advance.
View attachment 1715854817



Same as above but initial of 14* at 750 rpm.
The timing is probably in this range now.
View attachment 1715854818

38* at 3400 is not out of line for a iron headed big block. Yes the factory curve is more conservative. They had to cover all situations including pulling loads up steep mountains and things like that.
38* at 2600 rpm I think may be a problem when vacuum advance is connected. Its going to add up to a little more timing than it will really like in that rpm range. There's a reason that the factory slowed the advance above 1400 rpm. It wasn't needed or wanted. The engine gets more efficient and the flame grows faster from those rpms up.

Anyway. I'd leave the advance limit at its present setting. If you change it changes the spring tensions and I don't see the need at this point.
If your spring kit has some heavier springs with longer loops, you could try replacing one of the blue springs with a one of the longer looped springs.

Longer looped spring are the bottom row.
View attachment 1715854819
Goal is for the spring to have just a little bit of slack with the weights at rest (all the way in).
This spring should do nothing until the weights have moved out a few degrees. It creates the second stage of a shaped advance.
However this leaves just one spring responsible for holding the weights from moving outward at idle rpm.
I'm not sure a single blue spring will have enough tension to do that. If the weights move outward at say 600 rpm, then the timing around 750 rpm will not be the initial - it will be intial plus a several degrees advance.
So if using a long looped secondary spring, probably will need to combine that with a stronger primary spring. Assuming its the same Mallory springs as I've bought, I'd try Brown.

The kit came with two blue springs installed, and two each of the black and silver springs. Here are the graphs provided.

 

[Mattax]

The kit came with two blue springs installed, and two each of the black and silver springs. Here are the graphs provided.
View attachment 1715856041 View attachment 1715856042 View attachment 1715856043 View attachment 1715856044 View attachment 1715856045 View attachment 1715856046

That looks rings a bell but not from a Mallory or MP Mallory distributor.
Whose name on the distributor? edit. Bet its a Firecore. yes?
Can you take a photo of the springs? If they are what I think they are, they are not the same as the ones in my photos above.

 

[Righty Tighty]

The distributor is the Summit billet electronic distributor, part number SUM-851008. It's a Chinese made distributor, no brand name on it. When I get outside in a few, I'll send some pictures of the springs.

 

[Mattax]

The distributor is the Summit billet electronic distributor, part number SUM-851008. It's a Chinese made distributor, no brand name on it. When I get outside in a few, I'll send some pictures of the springs.

Interested in the loose springs so we can look at them side by side.

 

[Righty Tighty]

Here are the black and silver springs.

 

[Mattax]

Here are the black and silver springs.

View attachment 1715856674

A. Those are clearly different than the ones that were supplied by Mallory and MP.

B. Let's not put too much reliance on their graphs.

C. if you can measure the spring lengths, that will help a little. Calipers are great but just a side by side on the graph paper will provide a clue as to how much force to be expected.

 

[Mattax]

From now on when I refer to black, blue and silver springs it will be the ones that came with the Summit distributor.

Springs.
Thinner wire makes a weaker spring rate. That's obvious.
Less coils makes a higher spring rate. Extreme example is a slinky.
Larger outside diameter makes a weaker spring rate. These springs are all about the same in O.D.

The Length determines how much spring force is applied.

Comparing the summit black and silver springs.
Black has heavier wire, about the same number of coils (5 or 6) and coil diameter.
Its pretty safe bet that the black spring has a higher spring rate.
BUT
It may provide less spring force on the weight.
That depends on how long it is.

In Summit's photo it looks much longer.

Compare that length to the distance between the perches on your distributor.
Measure or install it and observe. See if there is a little slack with the weight at rest. I'm guessing there will be.
Then rotate the weight outward. Its important this spring begins to restrain the wieght before they've moved too far out.

You can stick a screwdriver behind either weight and twist it to observe the relation of the springs to the advance.

 

[Mattax]

The more difficult spings to compare are the blue and silver.
Before you do anything else, it will be worthwhile to check timing to determine the rpm it begins advancing.

If this chart is correct.

Then timing between 750 rpm and 3400 rpm will be radically different than my earlier guestimate.

Need to find out what's really happening there.
If you can find what rpm it begins to advance from 14 to 15 or 16 degrees, great.
Then get at least two more timing measurements further into the advance.
or measure every few hundred rpm, like 750, 1000, 1250, 1500, 2000. Whatever you are comfortable with doing.

 

[halifaxhops]

Hey I got springs!

 

[Righty Tighty]

The more difficult spings to compare are the blue and silver.
Before you do anything else, it will be worthwhile to check timing to determine the rpm it begins advancing.

If this chart is correct.
View attachment 1715856724

Then timing between 750 rpm and 3400 rpm will be radically different than my earlier guestimate.
View attachment 1715856720

Need to find out what's really happening there.
If you can find what rpm it begins to advance from 14 to 15 or 16 degrees, great.
Then get at least two more timing measurements further into the advance.
or measure every few hundred rpm, like 750, 1000, 1250, 1500, 2000. Whatever you are comfortable with doing.

Thanks for the explanation. I put some calipers on the springs and I got .570 on the silver and .740 on the black. I don’t have time today to play with timing, but I’ll get to it as soon as I can.

 

[Righty Tighty]

Finally had a chance to put the timing light to work. Idle is set to 650, 14 degrees advance. It held 14 degrees until 1800 RPM. At 1900-2000, I'm at 15 degrees, 2100 - 16*, 2200 - 17*. It's a little tricky doing this by myself and especially considering the timing mark is on the opposite side of the throttle lever (much easier on a small block).

Anyway, I decided to try to determine what my total was. I got 24* at 2800 RPM and it stopped advancing at that point. Why would I only get 10* mechanical advance? Am I doing something wrong here?

 

[67Dart273]

How far did you rev the engine? If you are uncomfortable doing that, temporarily remove the fan belt. Don't run the engine any longer than necessary to test. At least once during such a situation as determining if a dist is advancing, I buzz an engine up HIGH to the redline limits to see if the advance over advances, or scatters badly