Re: Rotor Phase

[jlandry@domain.elided (John A. Landry)]

The aliens commander decided "Allan & Kathryn Weidenheimer"
<allanw@domain.elided> would make a perfect specimen for dissection,
and he yelled...

>  OK, I plan to check my rotor phase, just for the exercise.  But,
>how can it be adjusted?  Maybe make slots in the plate that the points
>fasten to so it can be turned slightly?  Is there a factory adjustment?

I was hoping you wouldn't ask! <grin>

If you have the stock Holley gold box ignition, it's rather simple to
adjust the rotor phasing.  I know that's not the problem here, but it's
simple and I've done it, so I thought I'd cover it first in case someone
needs to know.  The reluctor (a.k.a. star wheel) in the distributor can be
rotated around the shaft by *carefully* tapping it with a brass punch or
drift after the distributor is partially disassembled.  As far as I can
tell, the reluctor is a simple press fit on the shaft.  All you have to do
is chuck up the part in a soft jawed bench vice and tap the reluctor in the
proper direction.  It doesn't take much!  Depending on which way you rotate
the reluctor (counterclockwise to advance, clockwise to retard - looking
from above), the point at which the gold box is triggered is changed.

Unfortunately, with a points distributor, the cam is fixed in relation to
the way the rotor points.  The cam and holder are ground as a solid piece,
so changes aren't possible there.  I should mention that I have seen
several different versions of this part over the years... each one having
the rotor pointing slightly differently in relation to the cam lobes.  I
assume this is to compensate for various rotor phase issues between
different models of distributors.  For example, two different distributors
with two different advance curves might need slightly different rotor
positions to adjust for rotor phasing.  Also, distributors having different
rotations would likely need different cams to compensate for rotor phase.
This is the danger of slapping just any old distributor in your truck...
either used or rebuilt.  You have no idea if the internal parts are correct
for your application or if the advance curve is correct.  And trust me...
neither does the warehouse that slapped it together!  Just look at the IH
shop manual some time to see how many different distributor model numbers
IH used.  It's mind boggling... and each one is likely slightly different
from the next.

Anyway I digress.  So what do you do if you find a breaker-point
distributor is out of phase?  Personally I haven't encountered the problem
to a great enough degree to have actually needed to correct it, so all I
can do is offer unproven suggestions.  The simplest things would be to try
loosening the breaker plate hold down machine screws and try shifting
(rotating) the plate a little before retightening.  You mentioned making
the slots in the plate wider, but I'd probably avoid that.  You have to be
careful and wouldn't be able to move the plate much because of the way it
interacts with the vacuum advance plate.

If you're sticking with breaker-points, you could go through the trouble of
carefully trying to relocate the entire breaker-point assembly, which would
involve redrilling and tapping the breaker plate.  But that's a job best
left to a skilled tinkerer.  And unfortunately you'd have precious little
control over how much change you made in the rotor phase.  It wouldn't be
fine tuning for sure.

I suppose you could just concentrate with the distributor cap and leave the
distributor mechanism alone entirely.  This is the way MSD addresses the
issue for popular Ford and Chevy applications.  They sell what they call an
"Adapt-A-Cap" which basically is an adjustable distributor cap.  It's made
so the top of the cap can rotate independently from the bottom of the cap.
That is, the terminals can be moved in relation to the distributor housing.

As I recall, the IH / Holley distributor cap locates on the distributor by
means of a tab from the vacuum advance bracket.  I suppose the slot in the
distributor cap could be widened to allow the cap to be rotated somewhat to
adjust for proper rotor phasing.  If the springs which hold the cap are in
good condition, I doubt the cap would rotate once set in place.  If this
did happen, the unused portions of the widened slot in the cap could be
filled with epoxy to make the slot the correct size.  What you would wind
up doing is simply repositioning the slot in the cap to correct the rotor
phase.  The more I think about it... the more I like that approach as it
leaves the distributor alone.

In the case of a Pertronix system, the same stuff applies, because you're
still using a breaker-point distributor.  I'm sure the rotor phase will
change somewhat when installing a Pertronix, but hopefully the change is in
the right direction so it isn't a problem.  I guess most of us get lucky.
But every once and awhile someone drops a Pertronix into a distributor with
rotor phase issues to start with, then the Pertronix shifts it toward a
worsening condition and the result could be a real PITA.

The other way one might adjust the rotor phase is through the rotor.  It
might be possible to change the tabs on the rotor somehow to slightly alter
the position of the rotor in relation to the shaft.

A lot of theorizing I know... but it's all I can offer.

Best regards,

John L.
-------------------------------------------------------------------------- 
jlandry AT halcyon DOT com      | 
Conservative Libertarian        |  "The road to  tyranny, we must never
Life Member of the NRA          |   forget, begins with the destruction
WA Arms Collectors              |   of the truth."
Commercial Helicopter - Inst.   |                     William J. Clinton
http://www.halcyon.com/jlandry/ |    10-15-95, speech at the Univ. of CT