308 Dwell???

Do you have a workshop owners manual? If so, refer to section "O" page 6. It gives the dwell details there.

 

The problem with those instructons on page O6 is that they garble "where you measure" with "which point set(s) is/are active" so they seem to give two different values for "R1".

When it says "on advanced breaker point R1 = 39 deg +/- 3 deg" that means when you hook the dwell meter onto the threaded post holding the wire coming from the R1 point and measure the dwell at idle (with R1 and R2 both active) the total dwell result should be the 39 +/- 3 deg.

When it says "On advanced breaker point R1, with retarded wire R2 disconnected from ground 34 deg +/- 3 deg" that means the dwell meter is still hooked up to the threaded post holding the wire coming from the R1 point, but the R2 point is disabled by unhooking the wire at the microswitch (so only the R1 point set is active).

So in your "R1 only" mechanical point system you'd use 34 +/- 3 deg for your dwell target

 

Joey
I have a 79 308 and I have been researching the same info. What I have concluded if you have single points or duel points with R2 removed the dwell s/b 34 degrees. (That's with only R1) The R1 and R2 settings (I think) refers to the setting for R2 when it is functioning and s/b 39 degrees or 5 degrees retarded while idling. When you start to push the accel. down a switch changes from R2 to R1 and that as I said s/b 34 degrees. Now I hope someone with more experience than I would correct me if I'm wrong. Please.
Where I'm having problems is setting the ignition timing. The info I found is any where from TDC to 7 degrees BTDC with only R1. I set mine at 7 degrees as suggested to me but I am having difficulity getting the car to idle. It is erratic and jumps to 2000 RPM then slowing decreases to a stall. I'm trying to adjust my carbs but can't because it won't stay at 1000 RPM. I read that with R2 functioning the timing s/b 2 degrees ATDC and that it may be difficult to adj the idle if R2 is removed. The reason I'm mentioning this is for you to be aware of this potential problem. Good luck and let us know how you make out and if you have any difficulty with the idle.

 

Isn't the timing set at extremely high RPM? I did mine a long time ago and recall running the car up to like 5 grand and setting the distributors with full advance in place. 7 degrees doesn't sound like the reading you should be shooting for. But its been a while. Hopefully someone with more recent experience can clear this up.

 

If you look at the R2 points, they are insulated from the distributor case. The R2 point only come into play when the microswitch on the throttle linkage is closed.

Disregard the R2 points for a moment.

When the R1 points are closed current flows through the coil and produces a magnetic field. When the points OPEN the magnetic field collapses and induces a voltage spike in the coil secondary. This voltage spike comes out of the big wire on the coil, through the distributor cap to the rotor, then through the rotor to the correct spark plug wire (and spark plug).

Setting the timing synchronizes when the points OPEN (thus inducing the spark) with the engine's mechanical position (+/- TDC). The static timing at idle, with the R2 points disconnected, is 7 degrees before TDC (marked PM on the flywheel).

Setting the dwell sets when the points CLOSE, and for how long (in degrees) they dwell closed. The dwell for the R1 points is 34 degrees. That means they are open for 54 degrees - the time it takes for the coil field to collapse and make the spark. This happens four times for each rotation of the distributor.

Now, back to the R2 points:

To control emissions, Ferrari retards the spark at idle from 7 degrees BTDC to 2 degrees BTDC. The R2 points do this by having their dwell set to 39 degrees (vs. the 34 degrees of R1). This extra 5 degrees of dwell must occur before the R1 points close. In other words, the R2 points must close 5 degrees before the R1 points close. This is set up by adjusting the position of the points in the distributor.

Setting the timing at 5000 RPM takes the R2 points out of the system (the microswitch is open) but does not verify their operation at idle (where you are having your problem). It also assumes that your mechanical advance is working correctly.

Here's how I do it:

First I set the dwell on the R1 points at 34 degrees.

Then I position the R1 points such that when they open the rotor is pointed directly at the notch on the distributor case. Then I check the dwell again, and repeat until I get it right.

Then I set the dwell on the R2 points at 39 degrees, with the R1 points disconnected.

Then I position the R2 points so that they close 5 degrees before the R1 points close.

Then I re-mount the distributor on the engine, and set the timing (with the R2 -> microswitch wire unconnected) at 7 degrees BTDC.

Repeat for other distributor.

Hope this helps

P.S. After 25 years and a lot of headache I bought a distributor machine. Its the only way to get this right.

 

P.S. After 25 years and a lot of headache I bought a distributor machine. Its the only way to get this right.[/QUOTE]

Mike
If I were to purchase a distributor machine where would one look? Isn't it's use for the most part obsolute since cars nowadays use computer stuff? Would you find one at a flea market or are they still produced new? I don't even know how big they might be for "Modern Iron" but have seen ones used on cars of the 30's and 40's. Don't you need an adaptor to hookup a Ferrari distributor? How much would I expect to pay? Any other info would be appreciated like name or additional equipment needed etc. Thanks.

 

Doc:

I got a 1955 Allen Synchrograph on the 'Bay for $100 plus $40 shipping. Then I rebuilt and restored the whole thing, which took a while. The biggest challenge was the electronics package, which used Tubes! After a long search I found someone willing to sell me a photocopy of the manual for $40 - pretty high, but you can't do without it.

Fortunately I have a buddy who is Mr. Tube and he helped a lot. Even after replacing the calibration resistors with modern precision ones the Tachometer and Dwell meters still drift, but I can attach my Sears Engine Analyzer and get good readings off that. I also use an Oscilloscope to check dwell.

I built an adaptor with $25 worth of parts from McMaster-Carr, and it works fine. What you really want is a stable mechanical system that will drive the distributor through a range of RPM to check the advance. You can use an external Engine Analyzer if the old elelctronics don't work.

The other option is to buy a rebult SUN machine, which costs $$$$. Robert Garven (also on this board) and I worked on getting our respective Allens to run, then he bought a SUN. He may still have the Allen and be willing to sell it. For my money the Allen has a better mechanical drive mechanism.

There are those who would say "for the same amount of money you can get a modern reliable electronic ignition system and retrofit it." and that's correct, but then again you can also probably get that nifty little Cadillac 4-valve V8 or even a Chevy small-block crate engine and retrofit that.

If you want more info you can PM me. I'll be happy to share what I've found out. I'm in Northern Nevada, and I don't often get to West Virginia, but hell, I'm open to anything.

 

Mike
Thanks for the info. I'll keep my eyes open for one locally. I know a few friends that restore antique cars and have some old service station equipment and can set up 30 to 40's distributors. I don't know if their stuff would work but they may be able to tell me how to use one if I can find it. I may get back to you for more info later. If you are ever comimg to the area drop me an email. Thanks again.

 

GREAT INFO IN THIS THREAD.... bump so i can find it ( i need to buy a darn printer ... mine is dead )