Oh, I'm just learning on this part; I thought total was total.

Currently, I set my timing with a light and with the vacuum advance line closed off. It is at 5 deg BTDC. Then, when I put the vacuum line back on the vacuum advance can, and rev her up, it doesn't exceed 30 degrees advance, so the timing light tells me. It seems to run well, idles pretty nicely, but the timing was set higher previously and it had more power.

Let me see if I understand this correctly, you're saying that I can go higher than 30 degrees total, just not initial total. Initial total is the sum of my dizzy position and whatever the mech advance is providing. So, e.g. if my mech advance is 20 deg, I might set the dizzy so I add 10 deg BTDC, to make 30 "initial". When the vacuum is back on it might be 50 or 60 and that's OK? Wow, I must be missing some additional power and performance, just waiting to be unleashed....

So, what does a stock dizzy provide mechanically? That is, when I install the spring kit and reduce that slot, am I cutting back on the mech advance? I understand the springs are too strong so the mech advance is spread over too wide an rpm range, right? The weaker springs allow more advance over a shorter rpm span, correct? What I don't understand is why I'm reducing the slot.

This is fascinating stuff, so many people out there have no idea how an engine works. I have some idea, just need the fine tuning from this wonderful brain trust of SL6er's to get it down pat.

Thanks all,

BG

The slot is the governor. It determines how much mechanical advance can be added to the Initial idle advance. Vacuum advance is load dependent. If the engine is under high load, vacuum will be shallow, and little will be added. At cruise throttle settings, vacuum will go deep, and more advance will be added.

Detonation is effected by cylinder fill. When the throttle plates are not wide open, vacuum will be deeper, or the pressure in the manifold will be lower. As you push on the go peddle, the throttle plates open more, increasing pressure in the manifold, thus the vacuum goes shallow.

At high manifold pressure, or close to atmospheric, flow is high, and cylinder fill is greater. This equates to higher cylinder pressures, and the need to delay ignition timing. The vacuum can backs off, and your timing moves closer to the Intial + Mechanical timing.

The springs determine when the advance occurs based on engine speed. Lighter springs bring the mechanical advance allowed by the governor in more quickly. Heavier springs resist the weights in the mechanical advance mechanism, so the engine has to turn faster to reach any given point on the advance curve.

My mechanical advance tips in at 1400 rpm, and is all in by 2400 rpm.
I am running a small "Hop out" with a slightly lighter spring on one weight than the other. This allows the curve to advance more quickly for part of the curve than the later portion. It's not much. My converter stalls at 2500, so I'm all in at the hit.



CJ

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Part of Tyrde-Browne Racing

Thanks for the schooling. I think I have it now.

Just out of curiousity, which color spring combination are you using?

I run a Mallory Unilite, so I'm no help!

Check in with DusterIdiot. He may know the combinations that give you the curve you want/need.

CJ

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Part of Tyrde-Browne Racing

Yes, finally, what is changing the slot width for? The weaker springs allow the mechanical advance to move more easily under centrifugal force, but why are we shortening the distance it can move in favor of turning the dizzy more advanced? I don't get that part. Thanks. D.Idiot?

The slots are the governor. They limit how far the weights move, and thereby how far the advance plate turns inside the distributor. Not narrower, shorter.

This limits the amount of mechanical advance that is added to the base timing. The base timing is what you set by rotating the distributor.

In other words, if you have a governor slot that allows the distributor mechanical to advance 15°, and you shorten the slots, now it only allows the distributor mechanical advance to add, say, 10°.

Longer slots would allow the weights to move further, rotating the advance plate more, and increasing mechanical advance.

CJ

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Part of Tyrde-Browne Racing

Got it.

OK, I must not have had my vacuum hose clamped off well enough last time. This time I definitely did, and my total initial advance looks to be about 20 deg. Here's my issue.

According the dist recurve chart, the stock slot (at .460 inches long) for the weights to advance of the stock distributor should provide about 25 deg. According to my readings, I have about 10 deg from turning the dizzy at idle, and when I rev er up, I get 20 deg total. This shouldn't be possible, the mechanical advance plus 10 deg should be about 35 deg total initial...hmmm. Maybe that strong (stock) spring is stronger than it appears? Maybe I didn't rev it high enough? I have an older rpm gauge, it pegs at 2400, but I'm pretty sure I was revving it up well past 3000. Thoughts?

Anyway, at least I know the safe range. I'll make the slot 0.380 as the instructions suggest for a SL6 and try the weaker spring combos, play with the dizzy advance.

Fun Stuff....

Typically max advance with a stock heavy spring (especially the points versions to prevent points float are heavier springs...), will be about 4400-5000 rpm on the clock before you max out the mechanical advance....

when tuning without the hose, just unplug it from the vacc. advance and put a screw or golf tee in the end of it and do the initial and mech adjustments.

You'll burn up about 1/2 a tank of gas dialing in the dizzy, it's a little easier if you have 2 of the same cores to make changes to. Nw you know why I bought a distributor machine (too bad they aren't cheap and easy to find anymore).

Good Luck,

-D.Idiot

OK, yes, now I have an extra core to play with. And thanks for the 4-5k rpm note. I was thinking of bumping the dizzy to get 30 deg total, but in the back of my head I thought...what if I'm just not revving it up high enough....? That stock (big) spring is pretty thick compared to anything in the recurve kit.

Now I have to see if I can get my buddy to tig the slots for me. I cut a nice steel bar stock key that fits in the end of the slot, just need to weld it in, saw it off and clean it up for 0.380 on each side.

Good thing the holidays are coming up, more time for my slant. Or as my wife calls it, my girlfriend. Actually, mine is a boy, my daughter named him "Donny Dart."

BTW, anybody know if the OEM dizzy gears are better/stronger than the newer ones sold on refurbished dizzys? I have a new core I'm recurving, but I also have a NOS dizzy gear/pin/washer still in the box - wondering if I should change that out while I'm recurving. I've already done this with my old dizzy as that's the one that shredded with the cam gear failure....or was it the dizzy gear that failed....hmmmm.

-BG

They were when they were new, but 20-40 year old OEM/NOS gears are going to be stiff and brittle. The Reman gear is the same as the new Dorman gear in quality, and I've run them up to 6000 rpm sustained without issue.

-D.Idiot

That's what Dorman says too, that they meet or exceed OEM specs on their dizzy gears...

Thanks for the confirmation. I will say when I put the NOS one on the current dizzy, it seemed pretty resilient when I drilled my hole, the shavings were not brittle. Still, I can't wait to get the recurved unit in there for a try.

When I pulled that wire snap ring out, it got pretty bent up though. I suppose if it bends, then I can bend it back in shape before reinstalling it. I've never seen one quite like that one. Snap rings should be made of spring steel.

I've seen old manuals that describe a little oil soaked cloth plug ("wick") in that hole where the snap ring goes, they said this is "essential" to properly lubricate the shaft. I assume the lube Dorman uses is OK, I don't need this little lubed wick?

See: http://www.classicwinnebagos.com/forum/ ... pic=3424.0 and scroll down to "The Lost Art of Maintaining a Mopar Distributor."

bg

It's how fast it cooks when bathed in hot motor oil that will be the test.
It's OK but not 100% definitive...I like how his picture in step 13 both pictures show EI distributors and not a points version for comparision, or a prestolite distributor (of course it's all for a V-8 so not 100% for us). He also fails to show the importance of the installation direction of the "notch" on the governor (on EI distributors it faces the direction of the light spring).

Felt wicks are hit or miss (seen lots in the distributors from 60's-1974, after that it becomes hit or miss). If you need one, you can go to a fabric store find some felt and buy a square and cut or punch a plug out of the piece for use in your distributor).

-D.Idiot