We all know there are 3 types of advance on these
distributors.... centrifugal, initial (or static), and vacuum.
To alter the centrifugal advance a distributor machine is required and won't be part of this paper. The initial advance is set by moving the advance/retard screw and plate on the side of the distributor. On '41 and older, the screw is on the passenger's side. To advance, move the screw upwards. On '42 thru '48, the screw is on the driver's side. To advance move the screw downwards. Under this screw is a plate that has several space marks that move as you move the screw up and down. There is also a single mark for reference on the distributor. Each of these marks is supposed to be 2 degrees, but I've found many that were 2-1/2 degrees, so don't rely too much on them. Stock distributors specifications are 4-1/2 degrees advance and are set on a distributor machine and run good. This is close enough for Government work, but souped up engines perform much better if tuned for the particular combination of equipment, octane used, and engine.
There are many methods
used to set the initial advance.
The method I use uses the engine itself to actually tell you where the advance needs to be for the specific engine. Let's get to it. Start by warming up the engine. Adjust the engine idle to 500-600 rpm. Connect a vacuum gauge to the intake manifold. Leave the vacuum line to the distributor hooked up. Loosen the advance/retard screw and move it up or down to obtain the highest vacuum reading. This it the maximum amount of initial advance this particular engine wants and will tolerate. Tighten up the advance/retard screw and your half way done. Make a note of the relation of the marks on the plate to the mark on the distributor for future use when rebuilding the distributor since this setting will never change unless you replace the distributor or make some engine mods. Now loosen the 1/2 inch screw on top of the distributor tower. This is nothing more than a lock nut for a 7/16" screw used to adjust the vacuum brake. For starters, turn the screw almost all the way out and leave the locking nut loose. Turning this screw outwards increases the effect of vacuum on advancing the timing (more advance). Conversely, turning this screw downwards decreases the effect of vacuum on advancing the timing (less advance). Take the car out and run it at a steady 35 or 40mph in high gear. Then nail it. If it detonates (pings), turn the screw downward and retest again. Keep adjusting until all signs of detonation disappear. Now turn it another 1/2 turn downwards and tighten the locking nut. And you're done. Loosely, and I mean really loosely, the vacuum adjustment adjusts the advance for the type of gas and the engine's compression needs. If you're on a trip and dropping elevation, you may have to turn this down a turn or two to prevent detonation. The same applies if you get some lower octane gas than you had when you set the distributor.
Incidentally, engines run cooler on low octane than they do on higher octane. If you having heating problems, you might try using a lower octane gas....
it may help.... rumble seat
rumble seat (Oct 31 1999 8:04PM)
RE: To Rumbleseat - advance
I think vouíre on the right track-. I'd pull the dist and check it out on a distributor machine. Then youíll know how much advance youíre getting and when it comes in. With some messing around while it's on the machine, you can probably tailor the advance to your wishes. The flathead has a lot of turbulence of the incoming charge of fuel/air mixture (a lot more than an OHV has) and, consequently, doesnít need or want a lot of advance. I usually stay about 4-5 degrees BTDC and limit centrifugal advance to about 23-25 degrees on street engines. As far as surging when cruising at 45 mph.... This is something that started showing about 10 years ago. It's prevalent in a variety of different brands of cars I've messed with. I think it's a combination of the gasoline (this is gas?) we get today and the total amount of advance. Many people Iíve talked to say it's not rich enough, but Iíve went from 051 jets to 068 jets in my daily driver small block Ford without any change in the surge. Since we're stuck with the gasoline, I've concentrated on the advance part. On your HEI.... If your distributor has a vacuum control, I decrease the degrees of advance the vacuum control does. This is done by pulling the rubber tubing off the vacuum control and inserting a small allenhead wrench into the exposed control orfice. Youíll feel the wrench slip into the diaphragm adjusting screw. Turn it clockwise (CW, or inward, until it bottoms. This results in the maximum amount of vacuum advance. Turning it counterclockwise (CCW) will decrease the amount of vacuum advance. On most engines I turn it CCW 4 to 4-1/2 turns. This will usually decrease the surge to a tolerable level. Some engines require the screw be turned out all the way. Many vacuum controls donít have the rubber tubing nipple. Instead they have a steel line screwed into a fitting on the vacuum control. Remove the steel line and fitting. Inside there is a spring and a couple or three of washers of different thicknesses. If I remember correctly, removing washers decreses the amount of vacuum advance. I usually just pull them all out and see what happens. If it's still not enough, Iíve been know to start cutting coils off-the spring. Crude, but Iíve had pretty good luck doing this. Messing with the vacuum control is not the best solution, but it's the only one Iíve found that works. Iíd be interested in anything anyone has to, say on the subject.... rumble seat
flatjack (Jan 10 2000 2:38PM) Timing early flatties Just read the article in BillB's Techno Page concerning timing 48 and older flatmotors. Have the following comments: 1.Vacuum advance; These dist. do not have vacuum advance as we know it today. The vacuum line is connected to a vacuum brake which limits spark advance under acceleration. With todays gas, you generally do not need this unless you have a pretty high comp. ratio. 2. Initial advance; Most flatheads like a total advance of about 24 deg. This is the sum of initial plus centrifugal advance. 32-41 dist have 15-17 deg while 42-48 have 23-25 deg in dist. Ford calls for all engines to have 4 deg inital advance. Now most engines want considerably more than 4 deg initial, especially with any kind of performance cam. This is because you have a relatively dilute, slow burning charge in the cylinder. 10 - 15 deg. initial will probably give you the best vacuum reading, so you would then have to limit centrifugal advance to get the proper total advance.
JD (Feb 5 2001 1:14AM)
I'm really out of touch with this, but did a ton of distributors and they are NOT all the same, look on the shaft end by the tongue, 11-A, 01-A and (what ?) 47 -A (?) Memory fails. These are the ones we preferred to tweak, and 11-A was the earliest advance ( as I recall) , and good for a cam that bleeding the pressure off. KEEP in mind we had GAS then, like Chevron white pump, I have no clue how to burn current stuff. Above, 24 deg max was mentioned, we used 28 to 30, so go figure.
The flyweights have leaf springs that can be tweaked, bent by finger no less, and change the advance curve a great deal. Each weight has two springs, a light one first followed by a heavy one, and you can make a stocker ping at any RPM you want, with or without the vac brake. With multicarbs, and no vac line, backing the adj screw clear out with no washers on the spring, and maybe squeeze the spring by hand to collapse it some. THEN use the leaf springs on the weights to set your curve with no other changes. Stockers need no help, mostly, and the stock adjustments outlined very adequate above will do.
The various degrees of heads, cams, carbs, and radical mods need some attention in the advance dept. Cams from 270 deg and up can use more than 5 deg initial, to fudge the final above 24, but mostly need the hole elongated in the brake plate, to allow the weights to go further. Point springs can be strengthened by bending, but we used a loose spring added from an old set of points for higher RPM without float. Do use a high melt point grease to hold that .016 point setting. I can't do all that without a distrib machine to tell me what the curve is, avoiding ping is the aim, but as much advance is it will stand.
You won't get it "right" the first time. If I remember, Harmon Collins mags were locked at 30 deg for alky, and push start meant turn the switch AFTER a reasonable RPM. --JD