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Distributor Cap Terminal To Rotor Clearance
https://slantsix.org/forum/viewtopic.php?t=60552		 Page 3 of 7
Author:  SlantSixDan [ Mon Jan 09, 2017 7:23 pm ]
Post subject:  Re: Added More Data & Brought Table To this Point
Quote:
Std IH-318 does not fit on slant distributor shaft (too small ID)
Well, dang. What do you see as far as its tip length?
Quote:
MO 6 and 2642986 data added to 60's info (note avg. gap at .020)
Looks like those older caps have much less eccentricity than the curent-production items (of course, the sample size of one makes it hard to say for sure).

What does "REMANUF Echlin 9" mean?
Author:  DonPal [ Tue Jan 10, 2017 3:36 am ]
Post subject: 
"What do you see as far as its tip length?"

By eye it is similar in length to the MO3000 and 1838516 from centerline to tip and longer than a typical aftermarket rotor. I needed it mounted to a distributor with a cap (already tested with a MO3000) to do a numbers comparison.


"Looks like those older caps have much less eccentricity than the curent-production items"

Less eccentricity and gap. The 60's combo is running an average gap of .019 (plus or minus .007) while the other caps with the long MO3000 are closer to .030 (plus or minus .010). Remember the HEI test data.....when we added .010 gap to the plug (.035 to.045) the secondary voltage doubled from 5000 to 10,000. Consequently your observation is notable even if the sample size hasn't grown big enough yet.

I'll put the MO6 and Chrysler rotor on my 65 test bed slant for a secondary voltage reading to see the double impact of the wider contacts and smaller gaps relative to the other important secondary voltage cases.

"What does "REMANUF Echlin 9" mean?"

This is the worst Echlin cap/rotor combo #9 (Echlin MO40 and MO13) that gave the 22000 secondary voltage .....after I machined all the terribleness out and brought it to a .015 gap (plus or minus .003) down from the .102 (plus or minus .012) big gaps. The .015 gap is a do-able target and not far from the just measured 60's combos so it wasn't a bad guess as to where the engineers wanted to go and achieved.
Author:  DonPal [ Tue Jan 10, 2017 2:07 pm ]
Post subject:  Gold Standard Data Results Outstanding
MO6 cap/chrysler rotor combo secondary coil wire voltage measured at 1400 to 2200 volts during the test. Data was added to the table. This is for points ignition (not HEI which will follow).

Note that the best Echlin Cap with the MO3000 rotor combo with low eccentricity had a similar gap but ended up with 6000-9000 secondary volts. So it might be logical to conclude that it wasn't the "aligned" small gaps that had the latest MO6 improvement in secondary voltage but rather the MO6 double width terminal which deals with rotor phasing during the various advance conditions more effectively.

The "aligned" gaps indicated in the table are when the rotor points directly at the distributor cap terminal.....but that only happens at one advance condition. At other advance conditions the gap increases as the rotor becomes less aligned with the terminal......note this test is at 1000 rpm with minor mechanical advance occurring since this distributor has the springs changed to hold back the mechanical advance initially.

So it's possible this test has defined the final target?.......extra terminal or rotor width can lower the secondary voltage down by more than 1/2 of what a reduced "aligned" gap can buy.

This makes a homemade super wide rotor made to reduce gaps to .015 to .020 and to handle the complete rotor advance phases.....as one possible approach to meet the Chrysler 60's challenging secondary voltage target.

Hopefully more 60's cap/rotor sample tests will help cement down the goal further.
Author:  matv91 [ Sun Jan 15, 2017 12:56 pm ]
Post subject: 
Image
Author:  DonPal [ Sun Jan 15, 2017 3:17 pm ]
Post subject:  Wide Width Rotor For Testing Secondary Voltage
Good Bulletin to see.......evidence of challenges in the past. There appears to have been some investigation when short rotors were introduced and field reports came in based on the Chrysler Tech Bulletin....wish they had put in some results of their testing and established gap & secondary voltage criteria. Would have been helpful data.

Meanwhile testing using Dan's idea to build an extra wide rotor starts with the below rotor which will be dropped into the best lowest eccentric cap found in the dozen or so caps tested so far.

The Echlin Cap #10 had the lowest eccentricity but larger gaps than the 60's rotor/cap tested so the MO3000 rotor with modified rotor tip has a tip that is .007 longer than the standard MO3000 long tip rotor.

The result is that gaps were brought in line with the 60's gaps measured.

Hopefully there will be temps around here in the high 40's to low 50's soon so I can do the test.

http://tinyurl.com/hj64bff

The rotor is crude because it uses common tools.

As far as everyone avoiding the jig building......if you can get a spare distributor and mount your favorite cap and rotor and then spin slowly while exerting side loading to the shaft.....you should be able to hear a hit and avoid the possibility of distributor gear damage when using an extended rotor tip like MO3000 or similar rotor.
Author:  SlantSixDan [ Sun Jan 15, 2017 3:19 pm ]
Post subject: 
matv91, that's an interesting TSB, but we need more info to figure out what rotors they're talking about. That would mean looking at rotor numbers in '74, '75, and '76 FPCs, and a check for TSBs published before this one to see where rotor tip length is first mentioned—it would be something like "There's a new rotor with a short tip used on
  • for
    • . This rotor [can, can't, shouldn't] be used for service replacement of the long-tip rotor, because [reasons]. Can you do some digging and see what you find?
      My FPCs go only up to '74 (used to have a '76…DusterIdiot, you still have it?)

      We have some inklings of what happened; the old 1838516 rotor in Donpal's tests has a long tip, longer than all the aftermarket replacements, which are probably built to the '75-'76 short-tip spec, which suggests the TSB, when we find it, is going to say the new short rotor supersedes the long-tip rotor going forward (also supported by the TSB matv91 just posted, which refers to the short-tip rotor as a running change).

      My guess is a shorter-tip rotor was specified to deliberately boost secondary voltage for more reliable ignition of the lean mixtures necessitated by the strangle-it-and-pray emission control strategy of that time. It's better to make the spark plug gap bigger, but the spark plugs available at that time wore too quickly with large gaps.
Author:  Killer6 [ Sun Jan 15, 2017 4:21 pm ]
Post subject: 
I dunno, seems clear to Me. We designed a rotor that makes the ign. less
reliable under less than ideal conditions, but we're stickin' w/it, and we
refuse to admit it's inferior. So we'll suggest that the fix isn't, then use the
weasel term "in most cases", to absolve ourselves from ever being wrong.
Dan's probably right, the extra gap was probably a cheap-ass secondary
KV booster, to accommodate the changes in the combustion environment.
Wasn't this the same time the heads switched to the external plugs?
Author:  DusterIdiot [ Sun Jan 15, 2017 5:17 pm ]
Post subject:  Yep...
Quote:
used to have a '76…DusterIdiot, you still have it?
Yep.

I see that the 1973 and 1976 manuals still use the 1838516 for the rotor part number... my 1978 manual shows the part number is 2979781...

I wonder when the part changed from the 565 to the 516 number?
Author:  DonPal [ Sun Jan 15, 2017 6:31 pm ]
Post subject: 
"I see that the 1973 and 1976 manuals still use the 1838516 for the rotor part number... my 1978 manual shows the part number is 2979781...

I wonder when the part changed from the 565 to the 516 number?"

If you want a late model 70's rotor tested to see where it's secondary voltage and gaps were give me a pair of numbers for a matched cap and rotor.

I'll try and get something that's old stock to take the aftermarket issues out of the picture. Seeing that bulletin about short rotors wants me to think this issue actually was launched by Chrysler and refined by the aftermarket?
Author:  SlantSixDan [ Sun Jan 15, 2017 7:05 pm ]
Post subject: 
Quote:
I dunno, seems clear to Me. We designed a rotor that makes the ign. less reliable under less than ideal conditions, but we're stickin' w/it, and we refuse to admit it's inferior.
That's not what it says to me, and while I can see how you might interpret it that way, you're guessing. So am I, until we dig up the doc that says what they did and why.
Quote:
Wasn't this the same time the heads switched to the external plugs?
1975.
Author:  SlantSixDan [ Sun Jan 15, 2017 7:09 pm ]
Post subject:  Re: Yep...
Quote:
I see that the 1973 and 1976 manuals still use the 1838516 for the rotor part number... my 1978 manual shows the part number is 2979781...I wonder when the part changed from the 565 to the 516 number?
Oops, typo (mine). Fixed.

So OK, that P/N info from the FPCs, together with the TSB, suggests they changed the spec (shorter tip) on the 1838516 as a running change. That would jibe with the old 1838516 Donpal checked being longer than all the current-production aftermarket rotors (which IIRC look just like the late-production Mopar items).

I bet somewhere there's a document (probably a TSB) on the subject. The more I think about it, the more I recall reading…something…that discussed this very subject: short-tip rotors introduced as a running change in Chrysler products in the mid '70s. I recall a side-by-side comparison images of the two rotors. What I don't recall is where I saw it. I thought maybe in the '75 Peterson book, but it's not in there. I'll keep digging.
Author:  SlantSixDan [ Mon Jan 16, 2017 7:25 am ]
Post subject: 
Found the relevant TSB number, date, and title:

082676 JUL 76 "Distributor rotor - design change"

How 'bout it, matv91, got that one?
Author:  DonPal [ Mon Jan 16, 2017 10:45 am ]
Post subject: 
"Found the relevant TSB number, date, and title:

082676 JUL 76 "Distributor rotor - design change"

The TSB that was already provided has:

Subject: Distributor rotor

Date: Jul 26, 1976

No. : 08-26-76

Looks similar to what you want to see??

I'm hoping for a TSB with enough detail to help mechanics determine if with a certain rotor & cap....... things are running according to Chrysler plan at a certain time frame & with whatever ignition system it was intended.
Author:  SlantSixDan [ Mon Jan 16, 2017 11:53 am ]
Post subject: 
Damn, you're right, that's the bulletin already provided. Not what's needed. I'll keep digging.
Author:  Killer6 [ Mon Jan 16, 2017 5:29 pm ]
Post subject: 
Lol, well You can call it guessing I suppose, I see it as interpreting based
on experience. I see phrasing & language like this all the time, there is
always a kernel of truth to the narrative that is intended to disguise an
unwelcome truth, namely the shorter rotor tip is less reliable in performance.
"Something else is weak/faulty & it's gonna go sooner or later",....what,
exactly? The engines being equipped w/the new rotor were practically new
w/ elecronic ign. when this bulletin was released, not a position of
confidence to suggest "upstream" failures in the making. While I para-
phrased the content in quotations, it is the spirit of the document. To be
honest, i don't know how many reports in the field it took to warrant these
TSB's at that time, but it wasn't just a handfull.
I would guess the documents as to WHY they made the change are
in a retired engineer's folder in a dusty box somewhere, or a technicians
training book/video, good luck finding them Dan! If anyone can............

P.S. Thanks to DonPal for embarking on this comparative endeavor!
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