Hey Guys,

A few months ago I came accross a post which lead me to a website that described how to make a new timing mark on your main pulley. IIRC it had a blue background and may have been done by an australian.

I know I saw it here, but after an hour of searching the forum, I can't find it anywhere. It seems like something I'd archive, but perusing the archive didn't bring it up either.

Anybody know the website I'm talking about? They take the pulley, put it on paper, draw two lines through it and a bunch of other things involving a protractor that I can't remember.....

Basically I think I've found one of my two timing marks, but I can't for the life of me figure out which one it is. If I can figure out which mark it is (if it is indeed a timing mark) then I can re-mark the other one by measuring 20* further or previous to it.

Jon

 

I may have it at home comp. but here's paul yaw's just in case. http://personal.riverusers.com/~yawpower/pultime.html

 

Jon, if you have a cloth metric tape measure, iirc, the pulleys are 360mm in circumference. It that's the case, mark 20mm on each side of the mark you found, then hit it with the timing light.

 

i know this has nothing to do with our cars but it does with the board, since changes aare gunna eb happening if im correct why not add a section with just websites that sell parts and stuff to do with rotaries and what helps us out...... just a thought ill find that suggestion place lol

 

Hey Jon,

Check your pm box. I sent you that link awhile back because I remember you were trying to mark your pulley. So you did read it here, just not as a post. Anyway, here it is again. It may help others as well.

http://ausrotary.dntinternet.com/for...ic.php?t=57491

Kent

 

Awesomeness.

Thanks Kent. I knew it was here *somewhere*. No wonder I couldn't search it up. I'm usually pretty l33t with my search skillz.

Jon

 

Distributor Advance Mechanisms
If your car has a distributor, it has two mechanisms that advance the timing based on manifold
vacuum, and rpm. Let's start with the vacuum advance. There are two vacuum pots on the side of
your distributor. One for leading, and one for trailing. Each of the pots is referenced to manifold
vacuum through a vacuum line or hose.
When the throttle plates are closed, or just partially open, there is high vacuum in the manifold.
The reason is that the engine, which is simply a pump, is spinning away trying to draw in air, but
since the throttle is blocking airflow, a great deal of suction or vacuum is present in the manifold.
This is the equivalent of plugging the hose of your shop vac with the palm of your hand. The
motor is spinning, trying to move some air, but since you are resisting the airflow, a vacuum, or
more specifically, a low pressure is created.
This vacuum, actuated through the vacuum advance pot will advance the timing based on the
intensity of the vacuum. As you open the throttle, the vacuum lessens, and the timing advance
decreases. At full throttle (Butterflies all the way open.) the vacuum advance has no effect on the
timing, because there is no manifold vacuum.
Centrifugal, or "Mechanical" Advance
In case you were wondering, centrifugal advance, and mechanical advance are two different terms
for the same mechanism. The centrifugal advance will advance the timing based on engine rpm. It
consists of two weights held in place by springs which are attached to the distributor shaft. At low
rpm, when the shaft is spinning slowly, the weights are held in place by the springs. As the rpm
increases, the centrifugal force of the spinning weights overcomes the spring tension, and allows
the weights to move outward. These weights are attached to the advance mechanism in such a
manner that as they move outward, the timing of both leading and trailing will be advanced. This
advance will begin at about 1,500 rpm, reacing maximum or "total" advance of approximately 20
degrees by 4,000 rpm, at which point no further advance will result from increasing rpm.
Why All the Complexity?
The timing requirements of the engine vary, based on charge density, rpm, and..here's the
biggy...emissions requirements! It is common to eliminate both advance mechanisms so that the
engine will be at full advance at all times. You will have a few less things that can fail, and setting
the timing will be less of a hassle. It is manily for these reasons that race cars run "locked" timing.
Setting Your Timing For Best Power
Now for the fun stuff. Most stock or mildly ported 12A's will make best power with total timing of 24
degrees before top dead center leading, and 16 degrees before top dead center trailing. 13B's
(GSL-SE.) Will normally run best at 26 leading, and 16 trailing. The timing for best power will vary
slightly from one engine to another, but a leading/trailing split of 8 degrees works best in almost
all 12A applications, and 10 degrees for a 13B. Since it is the total advance that we are concerned
with, this creates a problem because your stock pulley is marked at top dead center, and twenty
degrees after top dead center which is the factory recommended setting at idle.
$60 Pulley?
You don't have to buy an expensive aftermarket pulley just to have the appropriate timing marks. It
is quite simple to make additional marks on the stock pulley.
The first step is to remove the stock pulley. This comes off easily by removing the four 10mm.
screws that hold it in place. Some of the stock pulleys are indexed, and will only go on one way.
Others can be placed in any of four positions, (90 degrees apart.) so I recommend spinning the
engine to top dead center before removing the pulley so that you don't put it on wrong.
You will need a pair of vernier calipers, a small file or hack saw blade, a roll of masking tape, a
calculator, and some brightly colored paint. If you do not own a pair of calipers, this is just the
excuse you need to buy a set. Most retail tool supply stores carry them. They range in price from
$25 to over $200. Luckily, the $25 calipers are more than accurate enough for this application, and
once you have a set, you will be amazed at how often you use them.
Do not buy a set of plastic calipers from Sears or Home Depot. These are absolute crap, and
most of them are colored to look like stainless steel so you will buy them, only to find that they are
pieces of **** once you get them out of the package. A good set will have a small dial gauge, and
come in a protective plastic box. Note: Amtos is a good inexpensive brand.
Step by Step
1. Measure the diameter (Distance across.) of the pulley. This should be approximately 4.5 inches.
2. Take the diameter, and multiply it by 3.14. This will give you the circumference (Distance
around.) of the pulley
3. A full circle is divided into 360 degrees, so if you divide the circumference by 360, the answer
will be the distance around that equals one degree. For this application, 5 degree increments will
be fine, so divide the circumference by 72. The answer will be the distance around the pulley that
is equal to 5 degrees.
Example: If the pulley is 4.5" in diamter, 4.5 times 3.14=14.13. 14.13 divided by 72=.196. so .196 =
5 degrees.
4. Tear off a piece of making tape approximately 3 inches long, and stick it to a smooth flat
surface. Make a mark at the far left side on the edge nearest you, and label it TDC, for top dead
center. Using your shiny new calipers, set them at 5 degrees, which using the above example is
.196 inches. Make a mark .196 inches to the right of the TDC mark. This is your 5 degree mark.
Now multiply .196 by two (.393). Set your calipers to this number, and make another mark .393
inches to the right of the top dead center mark. This is your 10 degree mark. Now simply continue
to multiply the 5 degree number by 3,4,5, and 6 to get your 15, 20, 25, and 30 degree marks.
You are probably thinking screw that, I'll just set the calipers at .196 (5 degrees) and measure
from my last mark. Doing it that way will multiply your errors as you get further from TDC. If for
instance your mark is off by .005", and you make the same error every time, by the time you get to
30 degrees, you could be off by several degrees! Take your time and make it accurate!!!
5. Stick the tape to the pulley lining up your TDC mark exactly with the TDC mark on the pulley.
Looking at the pulley from the front, with TDC on top, your tape marks should be to the right of
TDC, and the factory 20 degrees after TDC mark (Trailing.) should be to the left.
6. Now take a small square, or triangular file and make a notch on the pulley at each of your
marks. Make sure that your notch is exactly centered on your pencil mark.
7. Dab some brightly colored paint into each of the notches. If you are using a spray can, you can
spray the notches, and wipe off the excess with some solvent and a rag. If you lightly wipe the
excess, the paint will remain in the low spots that you filed into the pulley.
8. Put the pulley back on the engine and you are done.
Setting the Timing to Total Advance.
Now that you have marks on the pulley, rev the engine above 4,000 rpm, and set the timing at the
appropriate spot. I mentioned 24, and 16 which of course is not marked on the pulley. It is easy to
eyeball this and arrive at any number you wish. If you are concerned about accuracy, you can add
as many marks as you want to the pulley, but I have found that marks every five degrees are
sufficient.
Final note: Turning the distributor changes the timing of the leading and tailing by equal amounts.
You should set the leading first, and then adjust the vacuum pot to set the trailing.
Don't be afraid to try different timing settings. Every combination is a bit different, and detonation
is not a concern in a naturally aspirated engine. If you do experience detonation, and the leading
is less than thirty degrees advanced, you probably have excessive carbon buildup inside of the
engine. Redline injector cleaner will do a good job of reducing this buildup, although it may take
several tanks to completely clean the engine.
Return to Main Menu.
Timing http://web.archive.org/web/200806010...w.yawpower.com...
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