[T3] odd issue RPM hangs.

[William Jahn]

Now I'm really confused. page 54 engine Bentley .

 A control in degrees -dist shaft
 B Vacuum in mm HG
 C RPM dist shaft
 D Vacuum in mbar
 a vacuum control curve
 b centrifugal control curve.

 So since the graphs only show dist speed we need to double that for dist
in engine speed right ?And the curve is what i see @ dist RPM . So b is the
one I should look at , the graph offers a variance of the curve  meaning
the low  end it could be is 8.5* to a high of 10.5* just like the AF(states
with dist installed) tells me it's double the dist speed if in a dist
machine, the begin where the advance should come in 1000 to 1200 engine RPM
then 1800 rpm advances 12-18* end RPM 4300 19-23*.

 Based on this you took the high end of the AH dist doubled the RPM 10.5* x
2 = 21* It seems if you read the graph's that actual total mechanical
advance does not exceed 21* all doubling the engine  RPM does is tell you
when the cut in speed starts I see 500 X 2 = 1000 RPM. Actually 1000 to
1200 RPM because they offer the low and high both being acceptable. I one
had a dist machine like Glenn Ring they would set the advance to begin @
500 dist RPM which is what the dist rpm is at 1000 rpm engine speed.

 I noticed what I think the issue I have is. On the Pertronix the magnetic
ring on the dist point lobe is not a tight fit, If I hold the shaft I can
rotate that ring close to 1/16" on the points cam and even though the rotor
sits down on that ring I can still move it and this would advance and
retard the timing in the same manner  as the mechanical advance would or
even the vacuum can moving the breaker plate. The ring does fit the lobes
you do need to rotate it for it to seat yet I can still rotate it. Either
they made it larger at some point because the instructions state rotate
till you feel it engage and use the rotor to force it down , this might be
fine if the cam lobe were new yet I doubt many are not worn down over 40 +
years. I don't see how I can shim it for a snug fit , can't glue it then I
can't remove it , it would need to be perhaps a thin coat of epoxy that
would not leave when heated applied then fitting super glue might fail from
heat. Or just take that pertronix out and go back to points. I only found
one brand of points made by ACDelco or Echlin brand from Napa. I have the
last set I used were Echlin , the Bosch set I got were the worst I've seen
nothing close to the German ones of days gone by or even the ones from
Spain. At least with point I can pull the dist and static time it , last I
pulled it a few days ago it would start then quit , took 10 tries for it to
stay running and I have no idea why . When it started then quite it ran
fine for the 30 seconds I had to pull the cap and rotate the crank for the
rotor to line up #1 and at 5 BTDC and it was still advanced yet started. By
that time if was flooded. When i had the pinging issue and put the AH back
in with a new O'ring  and the pertronix it fired right up still had to
retard it , I was just lucky.

On Mon, Oct 14, 2019 at 1:40 PM Jim Adney <jadney at vwtype3.org> wrote:

> On 14 Oct 2019 at 11:57, William Jahn wrote:
>
> > Jim , on the mechanical advance how did you come up with 21 degrees
> total.
> > I only have the Bentley yet it shows 6 degrees yet this is dist speed on
> a
> > machine so you double dist speed . I see the 72 dist chart dist installed
> > and it's near 21 degrees and has no graph . This means to me you can't
> > double the RPM and come up with 12 degrees. Or do you have another source
> > you get the full advance or is this what you have checked with a light
> and
> > recorded? I assume total being control in degrees dist shaft begins when
> > the advance first kinks in at RPM  not from the set 5 * BTDC or are you
> > just talking about 21 degrees is as far as the mechanical advance should
> > reach?:
>
> Looking at the Bentley recently, I just noticed for the first time that
> all the
> graphs are in distributor degrees while the charts for '72s are in
> crankshaft
> degrees. Bentley doesn't specify, but that's the only way these make any
> sense.
>
> The 6 degrees you mention for '73 is the vac adv, averaging closer to 5
> deg.
> The middle of the mech adv is ~10.5, which I doubled to get 21 crankshaft
> degrees of mech advance.
>
> To get the actual firing timing, you have to add the 5 crankshaft degrees
> BTDC at idle, plus any vac advance that comes into play. What this works
> out to is a max 26 deg of crankshaft advance under med or full load or 31
> deg under light load (cruising) when the vac advance kicks in.
>
> The FI vac advance only comes into play under med or high rpm and light
> load. We don't get any vac advance at idle or when accelerating or during
> hill climbing. It's only while the engine is "loafing" at highway speeds.
> That
> improves fuel economy on trips.
>
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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