Mechanical advance in old school C5AF-E distributor
 

I thought I might pose this question in a separate thread to my thread about rebuilding a 1960s Ford distributor (as not all of you may be interested in where to find lower distributor shaft bushings....:LOL:).

For reference: This is for a 1966 OEM C5AF-E distributor with mechanical advance in a 427FE with the "B" cam (.500 lift, .242 duration). Bore and stroke are both standard. Distributor was dual point and I converted it to pertronix ignitor ignition.

I have a question on the mechanical advance cam adjustment. My cam has two options, 15L (15 degrees distributor advance, 30 degrees at the crank) and 10L for (10 degrees distributor advance, 20 degrees at the crank).

When I removed the distributor, 15L was on the limit pin, but I don't know that it was ever advancing properly and knowing that FEs like 16-22 degrees of base timing (mine was set at 22, but I'm not sure I had much/any advance, assuming of course my dampner isn't slipping - I'll check that), it seems that adding another 30 degrees on top of that for a total of 52 would be WAY too much. Even with 16 degrees base timing, 46 total timing seems like it would be way too much.

Seems like I should rotate it to the 10L/20 degrees advance setting?

Thoughts?

And if I do this, as long as I rotate the assembly so that the rotor is in the exact same position as it was when I took out the distributor, the timing should be close to what I started with, correct?

For now, please don't post that I should upgrade to a decent distributor (new), etc. If this proves a big PITA to get dialed in correctly, I will come back and ask for the best FE distributor and I'm sure we will have another lively discussion. :D For now, I'd like to keep my engine as period correct as possible.

first let me just say i always limit my total to 38 with a keen ear for detonation, i'm at 4.125 stroke so my motor actually does better with less advance. you may be fine at 38 or even when the weather is cool, 40.

what slot to set the dist. at.....well actually either one, theoretically with a light car you can use the higher advance slot. personally i would use the lower advance slot, because we probably are not hurting in the power department at low rpm, so why kill the tires even more? right? JMHO

Fred

But this is the only way to set the advance timing, right? (Other than widening the advance slot a bit with a grinder if i needed to or buying a different advance cam). So advance of 30 seems crazy while 20 seems pretty close and I can get there by adjusting my base timing. (Oh, I will modify my details in the first post, but my bore and stroke are both standard).

you can put an adjustable vacuum advance on it too so you'll have more flexibility.

Ah, that's a good point. Except I don't have any vacuum port on my carb. There might be a plug that I can remove and put the fitting in, so I guess that would be something to explore. Thanks for the suggestion. I really will work to get it to run right as I like my original set-up.

OK, I got the distributor rebuilt and installed and advance works great now. Base timing is at 16, total timing at 36, all in around 2,500. Might be able to take a bit more timing, but feels good. I'll play around with it more later.

One strange issue though - the advance seems slow to come back down and a few times it has sort of "stuck" around 32 (still advances at RPM up to 36, but then only drops back to 32ish). It only seems to do this occasionally, but it some cases has stayed "stuck" even when I turned the engine off and turned it back on. But yet the advance mechanism couldn't be any smoother than it is. There can't be anything hanging it up.

I have a theory that I thought I would run by you all - I replaced the old springs with two replacement springs for this distributor from Mr. Gasket. (http://www.summitracing.com/parts/MRG-925D). They are the only replacement springs I found anywhere and they are a bit lighter than the OEM Ford springs. So my theory is that potentially the springs aren't quite strong enough to bring the advance cam all the way back at much more than idle RPM (can't explain why once it didn't come back after I shut the engine down :confused:).

Easy enough to test - try one heavier spring, except I don't know which other springs will work since they only list the one set for OEM distributors.

So what do you think about my theory? Any other ideas, anyone have a problem like this?

And, anyone have a recommendation as to which spring kit I can buy that will fit this application (otherwise I can just buy a bunch of them for $20 and see what works).

Thoughts?

Here is a close up of the springs that came in my MSD distributor cam and spring pack. Maybe?

http://www.clubcobra.com/photopost/d...springs001.jpg

I even measured them for you...
 

The lengths are as follows: Light Silver is 5/8", Blue is 11/16", Heavy Silver is 3/4". Now lemmee tell you, that heavy silver spring is heavy. I mean, I can't even pull it open with my fingers. I might as well be pulling on my Eibachs. If that heavy silver spring doesn't pull you back, then something must be wedged in there sticking it open big time.:eek:

I already opened it back up to verify that the mechanism was working properly. Everything is clean, lubed, swings super easily in there, maybe too easily, hence my theory as to the problem. The springs seem pretty light. Ever heard of anything like this? It's the only idea I have as to what might be causing this.

I'll go measure the old springs and see how long they are and then decide if any of yours might fit it. I only want enough tension to retard the advance when I'm off the throttle, but I want the advance in between 2,500 and 3,000. That beefy spring of yours might put be back to no advance......%/

EDIT: OK, no wonder it's opening to easily. BOTH the OEM springs are stiffer than the replacement springs. The lighter of the two is 11/16 and looks like it might have similar tension to that blue spring, so maybe I'll give that a shot. The heavy spring is 13/16 and can only slightly be moved with your fingers. So I guess an MSD spring kit is the right move and will give me some options.

And you know you can mix and match too. I run a light silver and blue, which is a pretty common choice. I know Pep Boys carries the MSD spring kits, if you have a Pep Boys near you.

But to answer your question...
 

But to answer your question, "No, I have never heard of a spring being so light that it didn't return the advance back to zero." Even a spring as light the one in a ball point pen should return the weights back to zero -- at least that's true with my MSD. But I don't know your distributor. Maybe somebody else here could opine....

I ordered them from Summit, so I'll see if it helps later this week. The only thing that really puzzles me is why they wouldn't return when the engine shut down. That only happened once, but I don't get how that's possible. Anyway, maybe someone will chime in with some other thoughts.

OK, in my experience with these cars though, nothing ever only misbehaves once.%/

This is an interesting subject. In the 60s when I was a teenager I used to play around a lot with Ford distributor advances. I kept a container of various Ford advance springs, and just threw them out a couple of years ago, thinking I would never need them again. :mad: Anyway, as I remember the light one was tight and returned the advance to zero. The second heavier one had play in it until the first lighter one advanced until the slop was all taken up in the second. You could buy after market springs that both had tension on them from idle on up. There is correlation between the springs and the weights. So, some springs that work in one distributor may not work in another. You might check Accell springs. They might be close.

You may have to try several springs before you get it right. "Right" meaning a smooth advance to about 2500-3000 rpms. What I used to do is graph it out. So, if you have say 3,000 rpms that you are shooting for, and you have 20 deg. in the distributor, and your idle is 1,000 rpms, then you would want that advance to start just above your idle range and be equal through that 1000-3000 rpms. That 2000 rpm range would be divided up by that 20 deg. or 5 deg. for every 500 rpms. It was easier to set these up on a Sun Distributor machine, but you can do it on the car if you have advance makings on your crank damper. It's easier to do with someone helping with the throttle, pausing at every 250 rpms and calling it out to you while you are watching the timing marks. Them you can see exactly what you have.

If your springs are to light the distributor will be advancing at idle. That throws you off. That's one reason to check your advance at idle, set at zero, and see if you hit 20 deg for full advance. If you are only hitting like 17, then it could be advancing 3 deg. at your idle. It's hard to get it all right on, so shoot for "in the ballpark." It can be time consuming but satisfying when you get it right.

Wayne

As Wayne described the light springs will often allow the weights to move at a relatively low RPM or because they allow static movement of the weights with the springs fully retracted. This will cause some of the available advance to be initiated before you get above the actual idle speed, thus limiting you to only have available 17 or 18 degrees of distributor advance. Sometimes because they have very little tension (light springs) the timing will fluctuate at low idle speed causing the idle to "Hunt" ie: raise up and down a little as the timing moves up and down a couple of degrees, this becomes worse and more exagerated with a long duration cam, open plenum manifolds and big carbs. The tangs on the base plate (attached to the shaft) can be moved a little to take up some of the free length of the spring and tweak the advance rate a little. If you are near a shop with a distributor machine (old school) it is much easier to create the curve you desire. Doing this is a dying art.

Ugh, you're killing me. ;)

Thanks for the info. Great to get feedback from someone who spent a lot of time with these distributors. I'll check out Accel. If they have set similar to the MSD, I may get those too and play with them. What I found interesting was how much stiffer the OEM springs were than the light replacements.

Any idea why the advance wouldn't have returned to just the base timing even after I shut it off? I still don't get why it wouldn't. The mechanism is very clean, lubed, etc. It all moves very easily.

Thoughts?

Mr Gasket offers the OEM springs on bubble packs.

DC how far off is it after shutting it down and restarting 2-3 degrees?

I spoke to a number of Ford distributor rebuilders last week looking for a few fasteners, etc that I wanted to replace and I'm sure a few of them could help me if I can't figure it out. One guy named Tim O'Connor seems to have a particular long time passion for Ford distributors. I spoke with him a couple times. That might be a winter project if I can't get it dialed in over the next month or so. It is an interesting subject and I'm not sure why there's not more written about it. I guess everyone has just gone to MSD/Mallory.

I think that's what I have (part#925D). They aren't OEM, they are super light, but that's the only Ford springs for these distributors that I found at all. Please let me know if I somehow missed one.

Do you have a vacuum advance distributor or was it modified so the vacuum advance was removed? If it was removed the points mounting plate needs to be secured so it does not rotate/shift. If that rotates the advance changes. Just a thought.

Wayne