Subject: [TR] Is My Distributor Worn Out?

From: "John & Pat Donnelly" <[email-masked]>
Date: Tue, 7 Jul 2015 20:13:52 -0700

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How do you know if your distributor needs to be replaced or rebuilt? I have
a Lucas 25D installed.

Is there a timing issue? What should I look for? Is there a test?

What the difference between a faulty vacuum advance and a bad set of
springs? 

I hate spending money when I don't have to.

Thanks!

Johnnie

'67 TR$A (no pun intended)

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nk=3Dpurple><div class=3DWordSection1><p class=3DMsoNormal><span style=3D'f=
ont-size:10.0pt;font-family:"Arial","sans-serif"'>How do you know if your d=
istributor needs to be replaced or rebuilt? I have a Lucas 25D installed.<o=
:p></o:p></span></p><p class=3DMsoNormal><span style=3D'font-size:10.0pt;fo=
nt-family:"Arial","sans-serif"'><o:p>&nbsp;</o:p></span></p><p class=3DMsoN=
ormal><span style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'>Is =
there a timing issue? What should I look for? Is there a test?<o:p></o:p></=
span></p><p class=3DMsoNormal><span style=3D'font-size:10.0pt;font-family:"=
Arial","sans-serif"'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span=
 style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'>What the diffe=
rence between a faulty vacuum advance and a bad set of springs? <o:p></o:p>=
</span></p><p class=3DMsoNormal><span style=3D'font-size:10.0pt;font-family=
:"Arial","sans-serif"'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><sp=
an style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'>I hate spend=
ing money when I don&#8217;t have to.<o:p></o:p></span></p><p class=3DMsoNo=
rmal><span style=3D'font-size:10.0pt;font-family:"Arial","sans-serif"'><o:p=
>&nbsp;</o:p></span></p><p class=3DMsoNormal><span style=3D'font-size:10.0p=
t;font-family:"Arial","sans-serif"'>Thanks!<o:p></o:p></span></p><p class=
=3DMsoNormal><span style=3D'font-size:10.0pt;font-family:"Arial","sans-seri=
f"'>Johnnie<o:p></o:p></span></p><p class=3DMsoNormal><span style=3D'font-s=
ize:10.0pt;font-family:"Arial","sans-serif"'>'67 TR$A (no pun intended)<o:p=
></o:p></span></p></div>
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** [email-masked] **

Archive: http://www.team.net/archive

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From: "Randall" <[email-masked]>
Date: Tue, 7 Jul 2015 22:57:25 -0700

> How do you know if your distributor needs to be replaced or 
> rebuilt? I have a Lucas 25D installed.

Hook up a timing light, start the engine, shine the light on the timing mark.  If it jumps around, the distributor is worn.  Slowly
rev the engine up while watching the mark.  It should move gradually and evenly until it's roughly 3/4" or 1" away from the pointer
at roughly 2500 rpm.  Again if it jumps around, or doesn't move, or immediately flops over to full advance, there is a problem
inside the distributor (eg bad or missing springs).

IMO this is a good test to run at every major tune-up.

Vacuum advance is much less important, it is mostly a fuel economy device.  To test it, you'll need to be able to hook up a vacuum
source (like a MityVac) to the advance module.  I don't know the TR4A specs offhand, but if it doesn't leak and you can get the mark
to move by at least 1/8" or so, the advance module is probably OK.  I usually don't bother to test this unless I suspect there is a
problem (engine seems sluggish at part throttle).  It only changes fuel economy a little bit, maybe 4 or 5 mpg at most, and mine
varies more than that just depending on where and how I've been driving.

For a more accurate test, take the distributor to an old time "Auto electric" shop that has the magic machine.  I bought one on
eBay, but haven't restored it to operation yet.  (Just got the on-car wheel balancer put back together, hope to try it out
tomorrow.)

-- Randall

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From: Geo Hahn <[email-masked]>
Date: Wed, 8 Jul 2015 06:06:53 -0700

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A worn distributor is a bit of a project to rebuild but a more common (and
fixable) issue I have encountered is sticky weights - this will show up in
the timing light test Randall describes and may also be detected by simply
twisting the rotor to the centrifugal advance position and seeing if it
returns when released.

I went so far as to try to plot the advance curve (crudely) by using a
timing light (with an advance dial) to see what advance I was getting at
various RPMs.

Randall <[email-masked]> wrote:

>
> For a more accurate test, take the distributor to an old time "Auto
> electric" shop that has the magic machine.  I bought one on
> eBay, but haven't restored it to operation yet.
>

Then a local friend put it on his Sun machine and that answered all
questions.   A marvelous device that looks like a prop out of a 50s Sci Fi
movie.  Used it to plot the advance curve and confirm that the bushing and
springs were okay.

Geo

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">A wo=
rn distributor is a bit of a project to rebuild but a more common (and fixa=
ble) issue I have encountered is sticky weights - this will show up in the =
timing light test Randall describes and may also be detected by simply twis=
ting the rotor to the centrifugal advance position and seeing if it returns=
 when released.</div><div class=3D"gmail_quote"><br></div><div class=3D"gma=
il_quote">I went so far as to try to plot the advance curve (crudely) by us=
ing a timing light (with an advance dial) to see what advance I was getting=
 at various RPMs.</div><div class=3D"gmail_quote"><br></div><div class=3D"g=
mail_quote">Randall <span dir=3D"ltr">&lt;<a href=3D"mailto:[email-masked]=
.com" target=3D"_blank">[email-masked]</a>&gt;</span> wrote:<br><block=
quote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;padding-left:=
1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-st=
yle:solid"><br>
For a more accurate test, take the distributor to an old time &quot;Auto el=
ectric&quot; shop that has the magic machine.=C2=A0 I bought one on<br>
eBay, but haven&#39;t restored it to operation yet.<br></blockquote><div><b=
r></div><div>Then a local friend put it on his Sun machine and that answere=
d all questions.=C2=A0 =C2=A0A marvelous device that looks like a prop out =
of a 50s Sci Fi movie.=C2=A0 Used it to plot the advance curve and confirm =
that the bushing and springs were okay.</div><div><br></div><div>Geo</div><=
/div></div></div>

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From: "Ann and Tim Buja" <[email-masked]>
Date: Wed, 8 Jul 2015 20:48:42 -0500

</lurk mode>

Johnnie asked:
> How do you know if your distributor needs to be replaced or rebuilt? I 
> have a Lucas 25D installed.

Randall replied
> Hook up a timing light, start the engine, shine the light on the timing
> mark.  If it jumps around, the distributor is worn...

Disconnect the vacuum hose from the vacuum capsule and hook up the timing
light sensor on the ignition coil lead so that every spark produced by the
coil will trigger the timing light.  Shine the light on the timing mark - if
you see a single mark that moves per the advance curve as you increase
engine rpm, your distributor is in good shape.  

If you see two marks that jump back and forth and change the gap between
them erratically, then your upper shaft bushing is worn out.  If the marks
move around relative to one another, you're seeing that the timing for #1
relative to its TDC is not the same as the timing for #4 at its TDC because
the shaft wobble is changing the point gap which changes the dwell angle and
the coil firing point at every revolution.  It's hard to get a car to run
well when the timing for every cylinder changes each time the points open.
Timing issues from a wobbly shaft can be cured with the installation of
electronic ignition (Crane recommended) but this is only postponing the
inevitable rebuild

If the mark(s) stay in a fixed position between 800 and 4000 rpm, your
mechanical advance is not working.  This could be due to frozen weights or
corrosion between the concentric shafts in the mechanical advance mechanism.
This will cause lousy performance above 2000 rpm.  You can check for this by
gently twisting the rotor shaft (you may want to remove the rotor itself so
you don't break the plastic key that holds in it a specific position on the
shaft).  You should be able to turn it about 10 degrees or so in one
direction against spring tension that returns it to its original position.
If it is firmly locked in place for both clockwise and anti-clockwise
rotation, the concentric rotor shafts are corroded together and will need
attention.

TR4s should see advance starting at 700-900 engine rpm.  The tables below
give you the min/max values for mechanical advance in distributor degrees at
distributor rpm when the distributor is on a distributor machine.  Multiply
by two for crankshaft degrees and crankshaft rpm when it's on the engine.
The 40xxx number is the Lucas model number that's stamped on the side of the
distributor body.

TR3/4		40698A
Dist	Degrees Advance 	
RPM	Min	Max
225	0	0
350	0.5	2.5
750	8.5	10.5
2700	13	15

TR4	61-62	40734A
Dist	Degrees Advance 	
RPM	Min	Max
250	0	0
450	3.5	5.5
1550	11	13
2800	14	16

TR4	61-onward	40795A
Dist	Degrees Advance 	
RPM	Min	Max
225	0	0
350	0	2
600	5	7
1200	9	11

Use this Excel spreadsheet to print your own advance curve for a variety of
Triumph cars.  Each tab in the spreadsheet is a different model distributor
http://www.snic-braaapp.org/media/DistAdvance.xls

If you plot the curve on the chart and you see a straight angled line with
no knee between two separate slopes, then you have incorrect springs inside
the distributor.  At rest, you should see two springs under the breaker
point baseplate.  One should be made of thin wire and should be tight on its
mounting pins.  The second spring should be made of heavier wire and should
be loose on the pins.  As RPM increases, the light spring controls the
advance at a steep rate until the pins move apart enough to contact both
ends of the heavy spring.  At the point, both spring control the advance at
a shallower slope.  On the tables above, this happens at 750, 1550, and 600
distributor rpm, respectively.

The maximum advance is controlled by a cam that will hit one of the spring
pegs at full advance.  It should have a number stamped on it to indicate the
maximum number of distributor degrees advance it will allow.  You should be
able to see this through the holes in the baseplate.  The distributor models
listed in the tables above should have 14, 15, and 10 degree cams,
respectively

With the engine running, put a vacuum gauge on the vacuum hose that you
removed from the distributor vacuum capsule.  Vacuum advance capsules should
have a vacuum source that provides zero vacuum with the throttle closed and
increasing vacuum as you open the throttle.  Vacuum retard capsules should
have a vacuum source that provides full manifold vacuum with the throttle
closed and quickly decreasing vacuum as you open the throttle.  Stromberg
carbs have the retard source near the throttle plate on the bottom of the
carb and the advance source on the top.  SU carbs have the advance source on
the bottom since throttle shaft rotates in the opposite direction from
Stromberg carbs.  If you get no vacuum at any throttle position, your vacuum
source is plugged or the hose has extra (more than two) holes in it.

Once you've verified you have a good vacuum source, have an assistant hook
it up to the distributor while you check the timing mark with the timing
light.  Advance units should be tested at part throttle, retard units at
closed throttle.  A Mity-vac usually works better for this test than the
vacuum source on the carb.

Shameless plug:
Come to VTR 2015 in Fontana, Wisconsin from August 11 - 14 where we will
have a vintage Sun distributor machine in action at our Distributor tech
clinic.
http://www.vtr2015.com

Tim Buja - Rockford, IL - 80 TR8, 73 Stag, 72 TR6
VTR 2015 Registrar and Tech Session presenter
<lurk mode>