Re: [xj-s] Advance & retard spring (long & definitive)

["Kirbert" <palmk@mailer.gadcomm.net>]

> From:          "Lee Opausky" <Opausky@netcom.ca>
> 
> John,  thank you for clarifying again the function of the "heavier spring"
> in digest #204.
> The reason, I believe, that this gets posted again and again, is that we
> have no way to tell if this spring is stretched - just a little or
> completely.

OK, here's one number for you:  I now have one of these springs in 
hand, and the critical dimension -- between the inside contact points 
of the outermost point on each loop in an unstretched condition -- is 
.734" (18.65mm).  Of course, I have no good way to determine if this 
particular spring is stretched; it is definitely not new.  But those 
of you who measure springs LONGER than this one can probably conclude 
that yours are stretched out of spec.

I also have identified the reason we think this spring might be 
stretched: our futile efforts towards getting the star wheel off!  On 
this distributor, the nylon clip in the center of the rotor was 
sheared and the inner half still in place, so it was probably apart 
before but nothing was providing any retention now.  So, if you just 
pull up on the star wheel (after removing the C-clip, wavy washer and 
U-clip) the whole rotor rises with it, and the springs on the 
centrifugal mechanism are the only things preventing it from rising 
farther.  If heavy pulling is applied, the spring is likely to get 
stretched.  If the nylon retainer ISN'T broken to begin with, then 
it'll probably break WHILE you're tugging at the star wheel, causing 
a suddenly-applied stretch to that spring.

Here's the method I used to get the star wheel off.  I used a claw 
hammer, with the claw itself under the star wheel and the head 
sitting on the rim of the distributor housing.  However, I didn't 
pull here; I only used the claw hammer to HOLD the star wheel (and 
the rotor) a little above its rest position.  Then I used a small 
tacking hammer to tap the shaft downward.  This worked well enough 
until the star wheel was high enough to be flush with the end of the 
shaft.  At that point I carefully selected a small socket with an OD 
slightly smaller than the shaft and set it on top and continued 
tapping.

This worked well, and did no discernable damage to anything.  Would I 
have tried it if it were my OWN distributor I was beating on with a 
hammer?  Actually, probably, although I probably would have tapped 
more gently.  It definitely appeared about the most gentle way I 
could think of to get that star wheel off.  I could imagine some sort 
of puller could work even better, but I didn't have one that could 
fit between the star wheel and the pickup structure.

> There is no quantitative measurement, nor a reliable
> descriptive explanation as to when ( at what portion of the total available
> travel on the rotor carrier shaft) this spring should start to stretch !

I don't have a quantifiable measurement, but on this distributor (the 
one that was sent to me by NE Classics for analysis) it's pretty 
obvious that the heavy spring is involved in the last few degrees of 
advance.  For those with their distributors apart and trying to see 
this, I'd suggest that you try to move the advance by manipulating 
the weights, not by turning the rotor carrier.

> Having carefully followed the postings on this in the last few months, I
> know that several of us have a rotor carrier shaft which comes to rest
> against the "thinghy" ( plastic thrust washer at the bottom of the rotor
> carrier shaft) BEFORE the heavier spring would stretch. If the plastic
> thinghy is the ultimate stopper for the total available travel for the
> rotor carrier shaft, then the heavy spring in these distributors do not
> "come into play" at higher revs at all, making the whole engine proned to
> overheating and mech breakdown at more spirited speeds.

Nononono -- the "thingy" is the stop at the IDLE end of the travel; 
it has no effect on the MAXIMUM advance, which is where the heavy 
spring is involved.

This is the first time I have actually seen an intact thingy.  
Interesting little device, actually.  I have now studied it quite 
closely, and have confirmed that the purposes suggested in my book -- 
mostly gleaned from others' descriptions and observations -- were 
completely correct.  It serves exactly two purposes:

1)  It's a thrust washer holding the rotor carrier shaft off the 
surface of the pivot plate on the distributor shaft.

2)  It's an inner (idle) stop for the centrifugal weights.

And I will stand by my original analysis: if this part is replaced 
with a suitable flat thrust washer (serving purpose #1) the car will 
run just fine.  It may not read the same on static timing and there 
may be a touch more noise from the distributor at idle, but since the 
timing on this car is set at 3000 rpm it won't make any difference at 
all above 900 rpm -- and the slight amount of additional retardation 
at idle may actually help pass emissions tests.

The suitable flat washer is more particular than I remembered, 
however, and I will be defining it more closely in the book.  The OD 
is critical.  In fact, I now am a little nervous about just what the 
hell I used in my own distributor years ago, and may take it back 
apart to see if I did it right.

I have also noted that it's entirely too easy to install the thingy 
(if you have one) incorrectly.  It has a pair of pins, and they are 
positioned immediately CCW of the wings on the cam plate, as viewed 
from below looking up (none of that will make a damn bit of sense to 
those of you who haven't stared at these parts!).  Offhand, it looks 
kinda like the pins should go immediately CW of those wings, and in 
fact the thingy can be forced on in that position, but it's not 
correct.

> I therefore fully understand why subscribers are inquiring for sources for
> replacement springs (no such thing), or at the risk of appearing $ cheap
> wanting to repair them (shorten the spring somehow)...

I'm betting it ain't possible, but I wouldn't be surprised if a 
substitute might be found.  If the unstretched overall length is 
correct, the advance curve will be correct up to the point where the 
heavy spring engages.  If the spring rate is the same, the curve will 
be correct the rest of the way to the stop.  If the spring rate is 
NOT the same, the slope of the advance curve will be slightly steeper 
or shallower from that point to the stop -- which probably means the 
advance might be off by a coupla degrees between 3000 and 4000 rpm 
and correct everywhere else.  Better than nothing, and probably close 
enough for government work.

This is a REALLY massive spring, more so than I remembered.  I'm 
gonna document everything about it that I can before reassembling 
this distributor and returning it to NEC.

> or just putting off
> the whole ( rather important thing as per Kirbert's book) overhaul of the
> distributor.

Heavens!  Don't do that!  Better to CAREFULLY disassemble the 
distributor using the claw hammer method described above, making sure 
not to stretch the springs during disassembly.  There is no way in 
hell these springs can get stretched out of shape in operation; the 
physical stop is encountered long before a significant amount of 
stress is applied to the advance.

> Can you complete your otherwise excellent comments to this effect?

Workin' on it.

> Not to muddy the issue, but I am beginning to believe that these heavy
> springs may not be stretched at all : too many ineffective heavy springs
> reported in relatively low mi cars and NO stretched or loose primary (light
> gauge) springs reported at all.

I believe this is entirely due to people turning the rotor carrier 
and watching the springs.  It simply won't move the heavy spring when 
you do this, but moving the weights themselves will show how the 
advance actually works.

> Should not the lighter gauge steel show
> signs of fatigue first?

It's even less likely that the lighter spring would get stretched out 
of shape.  Since it is thinner wire and a lot more loops, it can get 
stretched a LONG ways without threat of distortion.  Neither can get 
distorted in operation, and during disassembly if you pull hard 
enough to damage the light spring, the heavy spring is LONG gone.

BTW, I reported that the centrifugal advance on this unit was seized, 
but apparently it wasn't.  The rotor carrier shaft was not seized to 
the distributor shaft, probably because NEC had loosened it up and 
had sheared the nylon retainer in the process.  But the centrifugal 
weights were totally unlubricated, and the cam mechanism by which 
they move the rotor carrier shaft had enough friction in it that it 
could not be moved by turning the rotor from above.  It's entirely 
possible that it would move more or less correctly when running; the 
weights turn the rotor carrier MUCH more easily and effectively than 
the other way around.

As a practice exercise, I will be reassembling this unit properly, 
including lubing the cam plate and the weight pivots, and I'll see 
how it moves then.

 -- Kirbert      |     If anything is to be accomplished,
                 |     some rules must be broken.
                 |          - Palm's Postulate

---

References:

• [xj-s] Advance & retard spring
• From: "Lee Opausky" <Opausky@netcom.ca>

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