Subject: [TR] Distributor help

From: "Pete Ryner" <[email-masked]>
Date: Wed, 08 Apr 2015 19:51:11 -0400

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I have a =E2=80=9856 TR3 with a 40798B Lucas distributor installed.  It =
has been in the car for the last 35 years and has worked fine.  =
I=E2=80=99m cleaning up the engine while the body is out for paint, =
mostly detailing and fixing leaks.  It was rebuilt some time ago but has =
very low miles on it since the rebuild.  Anyway, I had the distributor =
apart to clean it up and found that the vacuum unit isn=E2=80=99t =
working.  I went to the big three to find a vacuum unit and my =
distributor isn=E2=80=99t listed.  In fact, I can=E2=80=99t find a =
reference for this distributor at all except that moss lists a cam to =
fit it under their TR3 section.  None of the vacuum units available are =
made to this distributor.  Can anyone give me an idea of where this =
distributor is used?  It obviously can be used in a TR3, but what is the =
difference from the ones listed in the parts books?  Finally, does =
anyone know of a place to find a vacuum unit for this distributor?  Any =
and old help is greatly appreciated.
Pete
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<BODY dir=3Dltr>
<DIV dir=3Dltr>
<DIV style=3D"FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">
<DIV>I have a =E2=80=9856 TR3 with a 40798B Lucas distributor =
installed.&nbsp; It has=20
been in the car for the last 35 years and has worked fine.&nbsp; =
I=E2=80=99m cleaning up=20
the engine while the body is out for paint, mostly detailing and fixing=20
leaks.&nbsp; It was rebuilt some time ago but has very low miles on it =
since the=20
rebuild.&nbsp; Anyway, I had the distributor apart to clean it up and =
found that=20
the vacuum unit isn=E2=80=99t working.&nbsp; I went to the big three to =
find a vacuum=20
unit and my distributor isn=E2=80=99t listed.&nbsp; In fact, I =
can=E2=80=99t find a reference=20
for this distributor at all except that moss lists a cam to fit it under =
their=20
TR3 section.&nbsp; None of the vacuum units available are made to this=20
distributor.&nbsp; Can anyone give me an idea of where this distributor =
is=20
used?&nbsp; It obviously can be used in a TR3, but what is the =
difference from=20
the ones listed in the parts books?&nbsp; Finally, does anyone know of a =
place=20
to find a vacuum unit for this distributor?&nbsp; Any and old help is =
greatly=20
appreciated.</DIV>
<DIV>Pete</DIV></DIV></DIV></BODY></HTML>

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** [email-masked] **

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

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From: "Randall" <[email-masked]>
Date: Wed, 8 Apr 2015 18:14:40 -0700

> I have a '56 TR3 with a 40798B Lucas distributor installed.  

What are the numbers on the vacuum advance unit?  There should be a 6 or 8 digit part number, like 54413565 and also a set of 3
numbers separated by dashes, like 2-6-3.  (Those are the number for the 40795 distributor, yours will be different but similar.  I'd
like to have them for my database.)

> Can anyone give me an idea of where this 
> distributor is used?

I have it listed in my database for 66-67 TR4A with high compression, but can't find any indication of that in the Lucas catalogs or
Triumph documentation so it is probably a mistake of some sort.  A little poking around with Google turned up applications like
Singer Gazelle and Hillman Hunter.

> It obviously can be used in a TR3, but 
> what is the difference from the ones listed in the parts 
> books? 

The functional difference will be the advance curves (both centrifugal and vacuum).  Compared to a 40480 (which is listed for later
56 TR3), the 40798 gives quite a bit less advance up to roughly 2500 rpm, then lets it go several degrees higher by 5000 rpm.

But of course, since the parts all interchange, it is quite possible that someone has modified the advance curve to almost anything.

Mechanically, it's a model 25D so there are lots of differences with the model DM2 that would be original to your 56 TR3.

> Finally, does anyone know of a place to find a vacuum 
> unit for this distributor?

Any of the 25D advance units will fit and work.  To be on the safe side, stick with one that provides roughly the same advance or
less.

Another alternative may be to have your local independent auto parts store send it out for rebuild.  I did that many years ago and
was very happy with the results.  The result looked and worked like new, and cost less than buying new.  Turnaround was 3 or 4 days
as I recall.

-- Randall

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From: "Randall" <[email-masked]>
Date: Thu, 9 Apr 2015 04:33:43 -0700

> I had the vacuum advance go out on my TR4a many years ago, I 
> could tell something was wrong,

I agree it makes a difference, but it is fairly subtle.  If you've never driven the car with a working VA, you might not notice
there was anything wrong.  And since it is only active at part throttle, it has no impact on maximum power or 0-60 time.  In fact,
it was deleted on later US-spec TR6 (from about 1972).

> you 
> could probably adjust the static advance to offset this 
> somewhat,

Not a good idea, IMO.  The reason the vacuum advance only works at part throttle is because it compensates for slower flame speeds
when the cylinder pressure is lower.  If you change the initial advance, that also affects full throttle operation, where pressures
are higher and you are more likely to get detonation.  Detonation can destroy an engine in a hurry, and isn't always audible.  BTDT,
got the broken piston.

-- Randall

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From: [email-masked]
Date: Thu, 9 Apr 2015 14:36:12 -0400

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In a message dated 4/9/2015 12:26:59 P.M. Eastern Daylight Time,  
[email-masked] writes:

Interesting that he says " I WILL NOT install a  Pertronix in a TR6 and 
will do everything in my power to talk you into using  points!!!"

I wonder why?

 
I asked Jeff @ Advanced Distributors that very same "why" question just  
yesterday because I saw it on the website and thought this represented a new  
position for him.
here is his response:
 
"RFI noise from plugs wires causes a misfire and I see it on the dyno.  
Put in points, gain power. Its a repetitive issue I see with insanely  
great regularity.
Jeff"

It so happens that I own a chassis dyno and literally less than an hour ago 
 had a customer TR6 on the dyno with a distributor rebuild by Advanced  
Distributors with a Pertronix ignitor in it. The car makes really good power 
and  has no miss anywhere in the power band and has a nearly flat air/fuel 
curve.  Time is money around here, so there is no way I'm going to put points 
in this  distributor to test Jeff's claim - this car runs great, so its going 
home with  the pertronix in it.  We have had many TR6s on this dyno - only 
a few  with Pertronix in them, but I have seen no evidence of misfire in any 
of them 
 
There are many "experts" in our hobby. Some may be wrong, but none are in  
doubt.  ;-)
 
Cheers,
Jack Mc
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<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>In a message dated 4/9/2015 12:26:59 P.M. Eastern Daylight Time,=20
[email-masked] writes:</DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: blue 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px"=
><FONT=20
  style=3D"BACKGROUND-COLOR: transparent" color=3D#000000 size=3D2 face=3D=
Arial>
  <DIV class=3Dgmail_extra>Interesting that he says "&nbsp;I WILL NOT inst=
all a=20
  Pertronix in a TR6 and will do everything in my power to talk you into=
 using=20
  points!!!"</DIV>
  <DIV class=3Dgmail_extra><BR></DIV>
  <DIV class=3Dgmail_extra>I wonder why?</FONT></DIV></BLOCKQUOTE>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>I asked Jeff @ Advanced Distributors that very same "why" question ju=
st=20
yesterday because I saw it on the website and thought this represented a=
 new=20
position for him.</DIV>
<DIV>here is his response:</DIV>
<DIV>&nbsp;</DIV>
<DIV>"RFI noise from plugs wires causes a misfire and I see it on the dyno=
.=20
<BR>Put in points, gain power. Its a repetitive issue I see with insanely=
=20
<BR>great regularity.<BR>Jeff"</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>It so happens that I own a chassis dyno and literally less than an ho=
ur ago=20
had a customer TR6 on the dyno with a distributor rebuild by Advanced=20
Distributors with a Pertronix ignitor in it. The car makes really good pow=
er and=20
has no miss anywhere in the power band and has a nearly flat air/fuel curv=
e.=20
Time is money around here, so there is no way I'm going to put points in=
 this=20
distributor to test Jeff's claim - this car runs great, so its going home=
 with=20
the pertronix in it.&nbsp;&nbsp;We have had many TR6s on this dyno - only=
 a few=20
with Pertronix in them, but I have seen no evidence of misfire in any of=
 them=20
</DIV>
<DIV>&nbsp;</DIV>
<DIV>There are many "experts" in our hobby. Some may be wrong, but none ar=
e in=20
doubt.&nbsp; ;-)</DIV>
<DIV>&nbsp;</DIV>
<DIV>Cheers,</DIV>
<DIV>Jack Mc</DIV></FONT></BODY></HTML>
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