setting points

I admit it, I was born into the age of the electronic ignition. But after reading Peter Egan's article in Road & Track this month about the lost arts of being a mechanic I am ready to learn one of these arts.

I am getting ready to replace the points in my new (to me) '73 911E and read in the manual about "dwell angle". What is this and how do I measure it? Thanks for your help.

Tom
'73E

You need 1 good set of feeler gauges be sure to have .012-.017"(.4mm + or -), 1 dwell meter preferably inductive pickup, 1 "L" offset 13mm wrench, this last is usually the hardest to obtain to turn the dist. base bolt the "L" is necessary(at least I never found a regular wrench that fit), 1 timing light(inductive is best)and 1 3/16" flat bladed srewdriver.
I always found it easiest to remove the dist. from the car. It can go in many ways, so be sure to know where the rotor is pointing when you pull it. Most manuals will tell you to be sure that the engine is at TDC on the power stroke for #1 cyl. but this is really not necessary as long as you replace the distributor with the rotor in or close to the position it was upon removal. Once out, fasten it in a bench vise(properly padded with a rag), remove the rotor(your replacing it anyway right?) and the dust cap if its still there, the points are held in by 1 screw with 1 slip on wire connection, R&R(remove & replace also clean while its all open and accessable this is a good time to check that the mechanical advance weights are free to move, lightly grease or oil them) so that the points will rotate with slight pressure from the screwdriver blade which is used as a pry(there is a small nub on the dist base plate which is used as a fulcrum), since the dist. shaft is free to rotate place the rubbing block on any convienient high spot(there are 6 to choose from) and put a slightly larger than desired feeler blade in( a little too big a gap is better than too small and it will tend to close up anyhow), then tighten the screw. My hand written notes for the Bosch dist say .012" but my Haynes says .016"( I think they are confused with the Marelli dist) and my Autobooks says .014". Just get it close(I would go with the middle #), the final adjustment will be done from the dwell meter anyway. Be sure to lightly dab some high temp. grease(it used to come in the little red(suicide) capsule with the points) around the dist shaft cam lobes.
Replace the dustcap and rotor, be sure that everything is seated properly, orient the dist. over its hole, rotate shaft so that the rotor point where you want it, due to gear coarseness you may have to fiddle one way or another. Reconnect the cap, snug up the dist. base bolt, start engine, check timing with a light. For the 2.4,2.7 and 3 liter engines the base timing is 5 ATC @900rpm with the vacuum hose connected(be sure to hook up to the #1 cyl.. The TDC(Z1) and 5ATC are close together on the crankshaft pulley I always put a dab of fluorescent paint or chalk on them so that they stood out with the timing light flashes(TDC(Z1) is on the right 5ATC is to the left. once the timing is ok then check the dwell which should be 38+or-3(Haynes says 40+or-3) The relationship between dwell and point gap is inverse ie smaller gap gives a larger dwell. If the dwell needs to be changed you can try to adjust in situ, but again it is so easy to remove the dist that I always did it that way.
Once dwell is satisfactry then recheck base timing and once that is ok check timing at 6000rpm which should be ~35BTC(vacuum hose disconnected)

One note of caution! I have a Permatune CDI and the instructions say not to use a dwell meter on a points ignition (where else would you use it?) as it can fry the CDI. Might be the same for the Bosch CDI or any other one you may be using.

Kurt V
72 911E

FWIW: Dwell is the percent of time the points are closed. The point gap IS the dwell. If you get the point gap exactly correct with a feeler gauge, the dwell will be exactly correct. Unfortunately, feeler gauges just get you close. Then, you use a dwell meter to get the gap exact.

------------------
'83 SC

just my 2c. you should learn to eyeball what .016 looks like. using a feeler gauge potentially oils the points, and causes premature burning. then check your skill with a dwell meter. it also saves time. after you turn 40 and need glasses, you have to learn to compensate for the magnification. damn.

Not to be too anal here, but the dwell (or cam) angle is the number of degrees of distributor shaft rotation the points are closed. The smaller the point gap, the larger the dwell angle. On a traditional points/coil ignition, the proper dwell angle (point gap) plays an important role in how much secondary voltage the system generates to fire each spark plug.

Dwell angle is less important on an electronic ignition as the points are merely a switch to signal the CD unit when to do its thing.

Sherwood Lee
http://members.rennlist.org/911pcars

Well said Mr. Verburg.
I have done this procedure many times & that's exactly how to do it.

I have a permatune CDI box too & read on their website that connecting a dwell meter can fry it.
Don't see how, the meter is just measuring duty cycle & should have a high input impedance.

Can anyone explain this.
I did connect a dwell meter to set the points gap BEFORE reading the warning on the Permatune homepage, the box survived.

JG

i've never fried one with a dwell meter. yet.

For an emergency .016 feeler gauge? The cover of a book of common folding matches...
A tip picked up on a midnight drag strip...it worked. Once home, got out the feeler gauges...yep, .016.

Thank you very much. You all have been a great help! I will keep practicing until I can sight it, while I am still young Mr. Walker. ;-)

Just to throw something else out there, has anyone tried the Ignitor that is sold on Pelican's site? A friend with another '73 was having installation problems with his as of last week.

Tom
'73E

One additional note. After you have the dwell setting correct and the points are set and the lobes have a little grease, take a clean business card and trap it with your points. Drag it thru to remove any oil or grease film that may have gotten on the points. Any foreign substance on the shiny new points can cause a non-firing ignition.

Jones Low
69-912
00-Box

Never heard of frying anything with a dwell meter before. But I bought an inductive setup as soon as I could afford it(25yrs ago that stuff was expensive, now its antique) just because i'm so lazy. John W. is correct about estimating the gap by eye, its amazing how accurate that instrument can be especially before one gets too old. A nice final touch is some Wurth electric contact cleaner.