Rick.
My prior employer is doing dist. work and I'd sent him your post and he
replied to me with this:
Spark advance is measured at the crankshaft (in crankshaft degrees).
Automatic changes in this reading are made by the distributor advance
mechanism with a 1:2 ratio (10 degrees at the dist. equals 20 degrees at
the crank). The changing speed of the engine, ultimately the speed of
the distributor, acts on the counterweights and springs, moving the
distributor cam relative to the points, thereby controlling how quickly
or slowly the advance occurs (typically at around 3000/3500 rpm). This
change, relative to engine rpm, can be graphed out and is referred to as
the "Advance Curve". Initial timing (or static timing) is then added
to the distributor advance figures to obtain "Total Timing Advance". It
is normally read in"Degrees Before Top Dead Center"(BTDC). If the
application has a vacuum advance or retard chamber, it usually acts on
the point plate, changing the position of the point relationship with the
distributor cam to change the timing relative to engine load (sensed by
engine vacuum). Since this is done within the distributor it also
occurs at a 1:2 ratio with the crankshaft and must be taken into
consideration with the total timing.
Ken Adams
If you or others want their distributors checked or re-curved contact Ken at
kcadams2@juno.com
Best,
Dave
On Wed, 2 Jun 2004 07:14:29 -0600 "frogeye" <frogeye@swcp.com> writes:
>
> Frogeye@SWCP.com Taos Garage Annex in Albuquerque
> '62 BT7 MK II, '54 BN1, '62 Fiat 1600S
> http://www.britishcarforum.com/TaosAnnex.html
> with the timing like. (Not a good thing according to the experts)
> >
> > I made a little compass gauge out of a piece of heavy paper stock.
> It has
> > degrees marked out in 10 degree increments. Anyway I looked at the
> rotor
> in
> > the distributor and held the compass over the center and rotated
> the rotor
> by
> > hand counterclockwise and it seems to hit the stop at no more than
> 20
> degrees.
> > So I can't see how the distributor could provide more than 20
> degrees
> > mechanical advance.
> >
> > I know there is a two to one relationship between the distributor
> and the
> > crank but I can't get my mind around the advance numbers. Does
> this
> correspond
> > to a 2 to one relationship between the advance measured on the
> rotor and
> the
> > timing light pointed at the crank pulley??
> >
> > So when someone says not to have more than 40 degrees of advance
> are they
> > talking distributor advance or crank advance?
> >
> >
> > Sincerely
> >
> >
> > Rick Neves
> > '56 BN-2
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