This is only to satisfy my need of always knowing all the theory behind all the practice. Exactly how a vacuum advance distributor works? is there some website that explains this clearly? I mean the whole process, not just, get the signal and advance.
Let's see if we can get a bunch of conflicting explanations going right here - that's always fun! For purposes of simplification, let's not get involved in dual-vacuum and let's just not even talk about how many cylinders and all that extra stuff. The faster the engine goes, the earlier the fire needs to be lit in relation to the compression stroke of the piston reaching the top and being propelled back down by the expanding burning fuel. If the engine is under extreme load such as pulling a hill, the timing of starting that fire needs to be a little bit later than when there is a light load. The distributor is the routing device for the high voltage electricity that will jump the gap at the sparkplug and ignite the fuel charge. Moreso, it is the timing device. What causes the high voltage to be produced in the coil is the rapid breakdown of the magnetic field across the secondary windings because the on/off switch - the points - suddenly got opened. The time at which those points lose electrical contact is the time the electricity travels through the coil wire, into the distributor cap, across the rotor, down the sparkplug wire to the sparkplug. Two possibilities on changing that timing: (1) centrifical advance mechanism is a couple spring-loaded weights that swing outward the faster they are rotated around the rotor shaft. The shaft is comprised of an inner and an outer shaft and they are keyed together by tabs on those weights. The faster they spin, the more "advanced" the part of the shaft the rotor is attached to relative to the lower part of the shaft, driven by the camshaft gear. That works fine to keep the timing of the spark correct by engine speed. We need something to adjust the timing for varying loads, however. That is where the (2) Vacuum advance (or as some call it, vacuum retard) comes into play. The points are mounted on a plate that can rotate slightly inside the distributor. As that plate rotates, it changes the angle of the points to the pointcam which is mounted on the upper part of the rotor shaft, just below the rotor. If we could rotate that plate to retard the timing of the points opening just a bit when climbing a hill or accelerating (Without interfering with the centrifical advance which needs to work according to speed - not load) we could give that fire a little bit longer to burn cleanly. When there is too much pressure, the flame tends to jump into multiple flamefronts instead of all going the same way and pushing the same way. By retarding that spark timing just a bit, we get a little more power and less possibility of multiple flamefronts which is destructive to the engine and raises temperatures dramatically. To rotate that points plate or breaker plate as it's called, a vacuum servo is used. This is ideal because an engine under load has less vacuum than an engine that is free-running. By calculating the precise number of degrees of rotation that is needed at whatever load and knowing how much vacuum is available at that load, a vacuum servo can be devised that has just the right amount of movement to rotate that breaker plate so the spark timing is correct. It's primary function is not to advance, but to allow for retarding the spark under load.
Is it all perfectly muddy now?
-- Dave "Busahaulic" Pearson Fall City, Washington Remove obvious from addy to e-mail
Karls Vladimir Peña wrote in message news:br39c3$27u5v3$ snipped-for-privacy@ID-209996.news.uni-berlin.de...
This isn;t another ploy to gather up troops aginst/for political discussion again is it?
'Cause I think, I'f I'm not mistaken, Al wasn't the one with the vaccum that got busy and made an advance..................
(Don't ry and pick on my sentence structure too much. I was just fine til I went to school to learn that the teachers knew less than the student.................in quite a few ways........LOL)
Remove "YOURPANTIES" to reply MUADIB®
formatting link
It's is not, it isn't ain't, and it's it's, not its, if you mean it is. If you don't, it's its. Then too, it's hers. It isn't her's. It isn't our's either. It's ours, and likewise yours and theirs. -- Oxford University Press, Edpress News
I would re-phrase that as "the faster you want the engine to spin", the sooner you want the fire lit.
No, if you need more power, you want the sparks to come sooner. If the sparks come later, your engine is retarded, you get less power. On a centrifical advance, you get sparks sooner when the engine is turning faster.
A vacume advance distrubitor is really a "low vacume advance" and "high vacume retard" distributor. If you are idling, the throttle plate is closed, causing high vacume in the intake (at the vacume port). The "high vacume retard" is in effect. When the light turns green, you step on the pedal, and open the throttle. The accelerator pump squirts, the fuel air mix gets rich... but rpms are still low. You want some spark advance for more power to crank up speed. A "low vacume advance" kicks in to make those sparks come sooner.
On a 009, you need the engine spun up the give the advance.
For any discussion of spark advance with various distributor options, , a novice might ask why you don't just make the spark fire sooner all the time, if it gives more power.
Partly because the process of combustion takes approximately the SAME amount of time, regardless of engine speed. That means there's a finite limit to how much advance you can use and get any power from the engine.
The goal is to have the combustion process over and done with during the period the piston 'dwells' at TDC.
You can work all this out for yourself using a clock (rpm) a piecea paper and a #2 yaller pencil :-)
Bob is spot on (as usual). At higher engine speeds different factors come into play (this is also load related).....BUT the chemical reaction of the combustion process occurs at the same rate. While the speed of the engine and the velocity of the charge flow into and out of the engine increases you will need to somehow manipulate WHEN the ignition begins to compensate for this. That's why you need a variable timing curve, generally the fast the engine spins the more advance you want.
The irony is that after a given higher RPM one must then begin to retard the timing.....but this really only applied to drag race apps or engines running on giggle gas. John C's notorious Squishy slugs allow for a quicker burn rate and don't need as much advance as normal. To reopen a festering wound, Bene Gerg's semi hemi heads are known to require gobs more timing to compensate for their slow burn. Slow burn? Who remembers Edger Kennedey and his famous slow burn "take"?
.............His last film was a few years before I was born. But I remember the 'slow burn' from his part in a few of the Laurel & Hardy flicks that show up on cable. You must be one of them 'film buffs' that I've heard of. Or, you're the oldest Olde Pharte to post here in a quadrennium.
Pretty funny that ye olde dust pharter should make such a snide comment!
He was also in plenty of Little Rascals flicks as well. Usually played a cop or an easily flustered or befuddled gruff character.
formatting link
Now I'm reallystrectching.......who knows Leon Errol?
formatting link
is my friend. Them and the green pills, not to beconfused with the little green men (the gray ones are much nicer, not asbrutal with the rectal probings)-ANT
Damn you guys are a lot older than I thought. Edgar Kennedy....wow I remember the little rascals etc...he was a veteran character actor. Geez I am
55......Rocket J. Squirrell sounded 25 but he just said he was
53..........wow.....this is an old phart club.........youths speak out........tell us your ages!!! Eric 68 Bug cabrio 62 Ghia cabrio.....next thing you'll tell me Jan Andersson is 25?
It's too difficult to start the engine, because the spark fires too early into the compression stroke, and cylinder trying to expand fights the starter motor.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.