Dwell Setting

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John Vardanian
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Dwell Setting

Post by John Vardanian » Wed Jul 06, 2011 12:51 am

It's been my experience that identical gap measures between the two sets of points do not necessarily mean equal dwell. Has anyone come across this? Thanks.

john
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kare
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Re: Dwell Setting

Post by kare » Wed Jul 06, 2011 3:54 am

When servicing my Marellis I came into same conclusion. I traced it down to each of the points making a contact in slightly different are of the lobe. So even if the single tringle cam is running both set of points, they run on different contour like there were two different cams. The difference should vanish when the points are broken in, but some the wear on lobes can still be different from lobe to another.

I can live with the error on mine; 1 degree or so.

Best wishes, Kare
250 GT 2+2 3197/GT

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John Vardanian
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Re: Dwell Setting

Post by John Vardanian » Wed Jul 06, 2011 1:39 pm

Thanks Care, that explains it. I noticed that the lobes are not exactly 120 degrees apart. They are off by a degree. So, the Sun machine is actually a pretty accurate device. Pretty imressive for an old dinasour!

Question then becomes, is it more important to have identical dwells as opposed to identical gaps?

john
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B24Spider
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Re: Dwell Setting

Post by B24Spider » Wed Jul 06, 2011 4:47 pm

I have a similar situation on some of my V6 Lancias, that is, a three lobe twin point distributor, except that a V6 is less forgiving than a V12.

If everything is perfect, proper gap gives correct dwell (Lancia didn't even specify dwell, just gap), and all that's needed is timing the distributor(s).

My own feeling is that rather than dwell or gap per se, it is at least as important that they "break" at 60* apart. That is, while gap affects dwell, and therefore the power at the plugs (sufficient recharge time), if there is sufficient power, and no impediments to discharge, then minor differences in charge between sets of plugs are less important than when (or where on the degree wheel) the charges are delivered.

As you've noticed, there is some discrepancy between the lobes, Lancias included, as well as wear between the distributor shaft and the lobe/advance shaft, and this is where the problem lies, at least for me. Finding and correcting this lobe geometry discrepancy and wear may not be practical, and thus one is left trying to find the best compromise. In my case, I'm still trying. I'm considering a Pertronix conversion on my spare distributor. There are also ignition boxes (MSD?) that will allow you to adjust individual cylinder firing points.
-Steve

DWR46
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Re: Dwell Setting

Post by DWR46 » Wed Jul 06, 2011 8:16 pm

Measuring the point gaps is just a mechanical method for setting an electrical adjustment. What is important is the degrees of dwell, as that determines the amount of coil saturation. The longer the time the coil has to recharge, the stronger the spark. Dwell is what is important, not the specific point gap. To do a Ferrari dual point, three lobe distributor correctly, I use my Sun distributor machine. First set one set of points to achieve a "normal" .014" gap. Then read the resulting dwell. Then set the other set of points to the same dwell, and do not worry too much what the resulting gap is. Realistically, if the gap is between .011-.017" then the second set of points is fine. If the resulting gap is below .011", the points may not "break" cleanly and you can get starting problems. If the gap is above .017", the points may "bounce" at high rpm and result in spark scatter and a high speed miss.

I generally do not rely on the Sun machine to establish the initial dwell as old machines may not be super accurate, but I use it to verify the dwell is the same for both sets of points. The nice thing about the Ferrari three lobe system is that it results in a sufficient amount of dwell and coil saturation to provide good sparks till about 8,000 rpm.

Be sure you always try to get the "old" style 4 spring points, not the later 3 spring variety. The 3 spring points will tend to "bounce" at high rpm.

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tyang
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Re: Dwell Setting

Post by tyang » Wed Jul 06, 2011 9:42 pm

B24Spider wrote:I have a similar situation on some of my V6 Lancias, that is, a three lobe twin point distributor, except that a V6 is less forgiving than a V12.

If everything is perfect, proper gap gives correct dwell (Lancia didn't even specify dwell, just gap), and all that's needed is timing the distributor(s).

My own feeling is that rather than dwell or gap per se, it is at least as important that they "break" at 60* apart. That is, while gap affects dwell, and therefore the power at the plugs (sufficient recharge time), if there is sufficient power, and no impediments to discharge, then minor differences in charge between sets of plugs are less important than when (or where on the degree wheel) the charges are delivered.

As you've noticed, there is some discrepancy between the lobes, Lancias included, as well as wear between the distributor shaft and the lobe/advance shaft, and this is where the problem lies, at least for me. Finding and correcting this lobe geometry discrepancy and wear may not be practical, and thus one is left trying to find the best compromise. In my case, I'm still trying. I'm considering a Pertronix conversion on my spare distributor. There are also ignition boxes (MSD?) that will allow you to adjust individual cylinder firing points.
-Steve
Hi Steve,

I am not a fan of electronic ignitions. When set up properly, they run great, but if there's a problem, it's a PITA to figure out, especially the Pertronix system. With the MSD, you're still using the points as a trigger, so the distributors don't have to be modified, but with the Pertronix, the points, and points plate have to be removed. Unless you manage to index the pertronix system exactly to the same spot as the points (nearly impossible), you can forget about a roadside repair by putting the points back in. If you're going to go Pertronix, get a spare module to keep in the glove box.

Call me old fashioned, but I like being able to troubleshoot points!

Tom

P.S. MSD takes care of dwell, and only looks for the opening event of the points to operate.
'63 330 America #5053

jcwconsult
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Re: Dwell Setting

Post by jcwconsult » Thu Jul 07, 2011 12:04 am

I am with Tom on this one. There is nothing wrong with properly set points. I used conventional points and a quality coil in a Pro Rally Volvo with 12.5:1 compression and a usable 5,000-8,300 rpm range for competition purposes.
Jim Walker
365 GT 2+2 #12451

kare
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Re: Dwell Setting

Post by kare » Thu Jul 07, 2011 2:49 am

The biggest problem with points is that people are afraid of them.

To me it is amusing to some extent that when I was a kid everybody including my mother was happily motoring with point ignited cars no matter if it was -40 degrees Celsius like in Siberia or +40 degrees like in Africa hardly ever experiencing a problem. Now - 40 years later - people are afraid to drive on a sunny weekend. They usually never really had a problem themselves but have carefully memorized every one they ever heard of like when a friend of a friend's neighbour was staranded on road side after the points gave in (which may in the end have turned out to really have been because of a flat battery caused by a faulty voltage regulator, but that piece of info was never spread as far and even if it was, the points can still break).

When I took my Marellis apart, I screwed an italian (heh) 360 degree wheel on top of the distributor, a hand in place of rotor and light bulb through points. I then adjusted the points plates exactly 180 degrees apart. Then I set both points at 0,4 mm and fine tuned the trigger points at 60 degrees slightly altering the gap on one set of points. I then found out that on one of the distributors one sparks is triggered about 1 degree later than others. I took it apart, mixed the parts a little and ended up exactly the same leading me to conclusion that that's how my distributor just is and I can live with that.

I was a little frightened when I opened up the distributors first time as every single screw including the top bering cover plate screws had been over-tightened. I soon figured that because one of the adjusting screws had been broken, somebody had tuned the carbs by moving the bottom plates which together with too tight fit over the shaft resulted quick and uneven wear of points (the contacts had hardly been broken in, but the lobe followers had been chewed up already!) the sparks all over as a result. The problem had then been addressed by over-tightening the screws without much help. Timing marks made by an iron saw on the outside of the distributors and a few hammer marks as well further prove that the main problem with my distributors were completely wrong pair of hands working on them. I'm quite sure that these hands go together with a mouth that spreads proven knowledge on how these Italian pieces-of-crap are good for nothing and loose their tune before you can say Saskatchewan. Thank heavens no hard to get parts had been damaged in a way that would harm the operation!

A person who may have worked on the car on one or more occasions once asked me how am I doing with the car. I said "pretty OK" but added that there was a small disaster hiding inside those distributors. Putting down his hammer he looked at me and said "Nothing wrong with those distributors". I realized that I was likely looking at the murder weapon.
250 GT 2+2 3197/GT

B24Spider
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Re: Dwell Setting

Post by B24Spider » Thu Jul 07, 2011 4:23 am

Tom, et al,
Thanks, I actually agree with you, for all the same reasons. I've never liked the idea of black boxes either, preferring points and coils as diagnosable, and repairable. I've put many miles on points, and the few times I've had issues I could always make it home. The closest I've ever come to installing an electronic ignition was CDs on stroker Saabs.

These distributors have no ball bearings. The distributor shaft/body clearance is well within spec on both my cars and spare, but there is more clearance and/or wear than I would like between the shaft and the lobe shaft. It's not that they're all that bad now, that same 1 degree, I've just been trying to get them .... au-point. I could chrome and grind the shaft, and hone the lobe shaft, but as I said, I have also been considering experimenting with a conversion as a way to side step this perceived lobe inaccuracy/lobe shaft wear.

Pertronix at least is reversible, only costs half what a cap does, and were I to try it, the original would be set up and sitting in the trunk, ready to drop in if needed. An MSD box, triggered by the points, would still suffer the same inaccuracies/wear.

However, Pertronix recently converted an Aurelia distributor for a customer car at a friends' shop, and, lo and behold, they included a spare pick-up. That speaks volumes.
-Steve

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tyang
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Re: Dwell Setting

Post by tyang » Thu Jul 07, 2011 6:05 am

The problem I've seen with Pertronix is when it's installed, care needs to be taken when installing the module close to where the points fire. There are at least three places to adjust the position of the distributor, so if someone slaps in a pertronix, adjusts the angle drive or distributor foot to time in the pertronix, simply putting in another distributor with points won't work. We had this problem with a 330 that was having problems with a Pertronix system. Even with a spare distributor set up for points, we couldn't do the swap without retiming the whole set up! There was not enough adjustment in the mounted distributor to get it to fire the points where we needed. I hope this makes sense.

I agree with Kare, people are afraid of points! Pertronix, MSD, and all the other electronic systems, spend a lot of money marketing their products. Add that to people used to 50K mile services on their regular cars, and you have a perfect reason to buy into their logic. I refuse to drink the cool aid!

I've tried Crane Cams, MSD, and Pertronix on my other cars with relative success, but with what I've seen working on Ferraris, I'm sticking with points on the 330 America.

Tom
'63 330 America #5053

tim
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Re: Dwell Setting

Post by tim » Thu Jul 07, 2011 12:15 pm

Greetings... I think one of the common problems that lead to Pertronix failure (and I've had 2) is the supplied voltage. I was told this by one of their techs. You need to bypass the ballast resistor and make sure all your connections are clean and tight (switch, fuses etc). Check the voltage as supplied to the unit and it should be close to battery voltage. I went back to one in my 66 Morgan, cleaned up all the connections, and used the Pertronix Flame thrower coil and so far no problems ( but I do carry a spare base plate with points mounted) . Off for a weekend of Morgan driving in Cambria for our annual MogWest meeting. Anyone in the neighborhood, stop on by. (white 66 +4) Tim
1964 330GT 5769 -the big yellow taxi 61&66 Morgan +4's Daimler SP250 and some other dull stuff plus a brand new Mini Cooper S Clubman JCWS

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John Vardanian
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Re: Dwell Setting

Post by John Vardanian » Fri Jul 08, 2011 12:40 am

Dyke, thanks for answering my question: identical dwell is more important than identical gaps. I also learned something today from you: do not rely on the accuracy of the Sun machine and manually set the first set of points to around 0.014" and whatever dwell that produces, apply that same dwell to the other points. Thanks.

john
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John Vardanian
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Re: Dwell Setting

Post by John Vardanian » Fri Jul 08, 2011 2:31 pm

Dyke, all the points I've gotten so far have the triple leaf spring and I noticed that the leafs are wider, to the point where they can sometimes touch the chassis and short ignition current. I wrap electrical tape around the leaf as a mitigation.

Does anyone know the story on the original four leaf, where to get them, etc? Thanks.

john
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DWR46
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Re: Dwell Setting

Post by DWR46 » Fri Jul 08, 2011 3:39 pm

John: Thanks for the kind comments about my recent post. The 3 leaf springs are what all the 3 lobe distributors originally came with. The 4 leaf springs are what came in the 6 lobe US distributors for the US spec emmission control Daytonas, etc. It is possible that Bill Young at GT Car parts may still have 4 leaf spring points available.

Ferrari felt that, when they "stole" one set of points to run each bank in the retarded timing position ( as triggered by a microswitch) required to pass the low speed EPA tests, the "high speed" set of points were then required to fire ALL six cylinders on each bank. The need for a 6 lobe cam, then required a stiffer point spring to keep the points from bouncing at high speeds. Once this 4 leaf spring became available, we all immediately realized that it would be "extra insurance" for high speed operation in the regular 3 lobe distributors.

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John Vardanian
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Re: Dwell Setting

Post by John Vardanian » Fri Jul 08, 2011 6:14 pm

Did not know that, Dyke. Thanks again.

BTW, changing the subject here, whatever became of 0851GT? What was different with the tail lights of that car?

john
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