Kelvin and all, thanks for all the help. I guess I'll save my self some
money by not buying a new vacuum advance and just go with the 16 degree
centrifugal advance and plug the vacuum port off. Actually this appears to
be what has been done to the one vacuum advance since it is full of a hard
epoxy type substance.
Thanks,
Ken
-----Original Message-----
From: Dodd, Kelvin [mailto:doddk@mossmotors.com]
Sent: Thursday, January 31, 2002 1:04 PM
To: 'Ken Waringa'; ptegler@cablespeed; MG
Subject: RE: Distributor choices - marking locations
Hey, this is fun. Thanks for playing too Paul.
Ok, Ken. A couple of ground rules.
1. There are no absolutes. Weird things have been known to crop up in the
production lines of England. What follows are general rules.
2. The original 5 digit distributer number identifies the assembly. That
is, it defines the vacuum and centrifugal advance curves. The statement
"but I have 2 different 25D4, 40987 distributors" indicates that one or the
other of the assemblies has been mucked with.
3. The 40987 dizzy was never specified for an HIF US car and neither of the
vacuum advances you have were original on the 40987 dizzy, which indicates
that neither of the units is original to the engine and both have been
mucked with.
That said. Typical characteristics for the HIF car would be...
Application, Distributor #, Vac Advance #, Vac Characteristics, Centrifugal
Advance, Operating advance at rpm
72 18V(584Z) 41370 54423989 7.13.3 10 16@1500 20@1700-2000
35@3300-3900 41@4800
73-74 18V (672Z) 41491 54425359 10.15.5 6 12@1500
16@1800-2250 32@3600-4050 39@4800
The problem is that there is no new sourcing for a distributor that will
meet these requirements. There is a great new unit available to fit the
1962-1971 HS equipped cars, but it will only work with a ported vacuum
source.
Someone correct me if I am mistaken, but I've come to a conclusion that the
easiest thing to do on an HIF or Stromberg equipped car is to go with an
early distributor set up modified for Centrifugal advance only. This sounds
like what was done on your two engines. Set up with the early static
timing, you will get good starting and drivability. The only down side is
you would not get the fuel efficiency advantage the vacuum advance gives at
cruising speeds.
Check out the chapter in Burgess's "How to Power Tune MGB 4-Cylinder
Engines" for a really good explanation of the the different curves.
Note: Burgess specifies chrome bumper vs rubber bumper. The US models
started to use manifold vacuum advance on the HIF equipped cars, not when
the bumpers changed.
One of these days I want to get a test machine, so I can run some of the new
available units and get some real data rather than running off at the
keyboard with what ifs.
Hope this clarifies rather than confuses
Kelvin.
> -----Original Message-----
> From: Ken Waringa [mailto:kwaringa@dynsys.com]
> Sent: Thursday, January 31, 2002 4:54 AM
> To: ptegler@cablespeed; Dodd, Kelvin; MG
> Subject: RE: Distributor choices - marking locations
>
>
> Last night I had a chance to clean both vacuum advances
> looking for numbers.
> The vacuum advance that came off the distributor with the 10 degree
> centrifugal advance had the following numbers: 10 15 5;
> 54425359. The
> advance from the distributor with 16 degree centrifugal
> advance had: 2 6 3;
> 54415328.
>
> Now. Looking at these numbers and studying Paul's advance
> chart it seems
> that the 10 degree dizzy has much more vacuum advance at
> lower engine rpms.
> The 16 degree dizzy will have significantly less advance at
> idle and relies
> more on the centrifugal advance than on the vacuum advance.
>
> Both vacuum advances are shot and will need to be replaced.
> Kelvin, looking
> at the Moss catalog they only list one vacuum advance for
> each distributor
> type, but I have 2 different 25D4, 40987 distributors. Do you have a
> listing of the vacuum advance numbers that are available?
>
> And back to my original question, which distributor will be best for a
> stock, street driven early 1974 MGB engine with stock HIF
> carbs? Will it
> make any difference which one I use?
>
> Thanks,
>
> Ken
>
> -----Original Message-----
> From: owner-mgs@autox.team.net
> [mailto:owner-mgs@autox.team.net]On Behalf Of
> Ken Waringa
> Sent: Tuesday, January 29, 2002 6:17 AM
> To: ptegler@cablespeed; Dodd, Kelvin; MG
> Subject: RE: Distributor choices - marking locations
>
> Thanks, I'll try to find the numbers tonight. They are very
> different in
> appearance. The one on the dizzy with the 16 degree advance
> looks like the
> one pictured in the Moss catalog. The one on the dizzy with
> the 10 degrees
> of advance has the vacuum line connection to one side (not
> centered) of the
> vacuum advance.
>
> Thanks,
>
> Ken
>
> -----Original Message-----
> From: ptegler@cablespeed [mailto:ptegler@cablespeed.com]
> Sent: Monday, January 28, 2002 4:43 PM
> To: Dodd, Kelvin; 'Ken Waringa'; MG
> Subject: Re: Distributor choices - marking locations
>
> ...and some are stamped around the neck of the
> vac unit right up at the nipple where the vac line
> attaches.
>
> Paul Tegler
> wizardz@toad.net
> www.teglerizer.com
>
> ----- Original Message -----
> From: "Dodd, Kelvin" <doddk@mossmotors.com>
> To: "'Ken Waringa'" <kwaringa@dynsys.com>; "Dodd, Kelvin"
> <doddk@mossmotors.com>; "MG" <mgs@autox.team.net>
> Sent: Monday, January 28, 2002 5:03 PM
> Subject: RE: Distributor choices
>
>
> > Ken:
> >
> > The numbers on the advance units are very hard to see. They are on
> > the face towards the distributor (if I remember correctly)
> and may need
> some
> > emery cloth cleaning to become visible. They are there.
> >
> >
> > Kelvin.
> >
> > > -----Original Message-----
> > > From: Ken Waringa [mailto:kwaringa@dynsys.com]
> > > Sent: Monday, January 28, 2002 9:00 AM
> > > To: Dodd, Kelvin; MG
> > > Subject: RE: Distributor choices
> > >
> > >
> > > Kelvin and all. I looked at the vacuum advances from both
> > > distributors, but
> > > could find no numbers or identification markings on them. I
> > > reconfirmed
> > > that both are 25D4 distributors, the only outside
> difference is one is
> > > marked 40897 A and the other is marked 40897 E. The internal
> > > centrifugal
> > > advances are different though. The one with the A is marked
> > > 10 degrees and
> > > the one with the E is marked 16 degrees. The mechanical
> stop for the
> > > centrifugal advance is clearly different as well.
> > >
> > > If anyone could advise which of these distributors would be
> > > best on a stock
> > > street car. I plan to use the HIF carbs on the car.
> > >
> > > Thanks,
> > >
> > > Ken
> > >
> > > -----Original Message-----
> > > From: Dodd, Kelvin [mailto:doddk@mossmotors.com]
> > > Sent: Wednesday, January 23, 2002 2:14 PM
> > > To: 'Ken Waringa'; MG
> > > Subject: RE: Distributor choices
> > >
> > > Ken:
> > >
> > > Someone out there please double check me, cos
> I've got a 5pm
> > > deadline and can't spend any more time on this.
> > >
> > > The records I have show the 40897 dizzy as being
> > > original fitment on
> > > 62-67 MGB definitely not for the 74 cars you have. Lucas
> > > shows a 41288 unit
> > > as the superceded replacement. The first 5 digits give the
> > > part number, the
> > > suffix is not used for identification.
> > >
> > > Any unit with the same 5 digits should be
> identical, given the
> > > vagaries of production line, later modification and divine
> > > intervention.
> > >
> > >
> > > Based on dubious years of swapping bits, I'm banking
> > > that both your
> > > engines got dizzy swaps from the original rare bird 41491 to
> > > the much more
> > > available earlier unit.
> > >
> > > If you get me the part numbers off the vacuum advance
> > > units which
> > > may be 54411230 with the following legend 5.13.10 underneath
> > > I can be of
> > > more use.
> > >
> > > The problem is what carbies are you using? HIFies, or HS?
> > >
> > > It sounds like you may have a common case of mix and match,
> > > and you are
> > > asking the right questions to figure out what combination
> > > will work the
> > > best. First we gotta figger what you really have.
> > >
> > >
> > > all the best
> > >
> > > Kelvin.
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