Dear Pip,
I still had little problem of oil leak from Cyl.head after
modern seal conversion, so I add another seal at he bottom of
vertical drive housing (upper york needs to be machined as
well), it perfectly works.
Best regards,
Hiro
>
> From: "Pip Bucknell" <mgwizard@caloundra.net>
> Date: 2002/10/31 木 午前 06:45:20 GMT+09:00
> To: "Pat Mullen" <pmullen@telus.net>
> Subject: Re: 3 brush dynamo
>
> Pat,
>
> That is a nice, clear and simple explanation.
>
> Thank you for your contribution.
>
> There is one other issue that I have found important to the
operation of the generator. It is not electrical but it is
important. That is the problem of oil leaking from the
overhead drive.
>
> I have held the belief for a long time that it is static
leaking that causes the major problem. I say this, because
when the engine is running at speed, any oil problem is thrown
out by the spinning generator yolks & other fittings and can be
seen on the radiator. However when the engine is not running,
the oil finds its way into the generator and seems to cause
numerous problems.
>
> Many of us have made alterations to the oil seal for the
overhead drive. My mechanic changed mine from the common
practise and we have never had a problem. I have taken the
engine to 8500 revs on a number of occasions when I have become
"excited" and this does not seem to worry the generator at
all.
>
> Anyhow, again, thank you for your contribution.
>
> Hopefully we will be back in Canada in another few years and
we can see the progress on the NB. Regards
>
> Pip
> AUSTRALIA
> ----- Original Message -----
> From: Pat Mullen
> To: hiro@octagongarage.com
> Cc: mg-mmm@autox.team.net
> Sent: Thursday, October 31, 2002 7:02 AM
> Subject: Re: 3 brush dynamo
>
>
> Hi Hiro,
>
> How good to hear of a fellow MMM enthusiast who REALLY
drives his car!
> (I used to own a 1933 J2 and then a 1934 J2 in 1952-54 when
I was a
> student in England - I am now a Canadian with a 1936 NB
nearing the end
> of a complete restoration).
>
> For some 30 years, between about 1936 to 1965 prior to the
advent of
> alternators, and after the MMM cars had finished
production, British
> cars controlled the VOLTAGE output from their dynamos with a
> "Compensated Voltage Control" (CVC) device. This measured
the dynamo
> output voltage; the CVC control mechanism was placed in
series with the
> dynamo field coil, between the dynamo + and - terminals.
There was no
> "third brush". It worked quite well.
>
> Prior to this, in the days of our MMM cars in the early
1930s and
> before, the CURRENT was controlled by the third brush
method in such a
> way that changes in engine speed made comparatively little
change to the
> current supplied from the dynamo.
> The only ways to control the current on an MMM car were by
> (a) moving the third brush while doing maintenance on the
car
> (b) switching resistance and or out of the field coil
circuit, usually
> using the lighting switch.
>
> Here is an explanation of how method (a) worked on a
negative ground
> ("earth") car like our MMMs:
> 1. On ANY dynamo, third brush or CVC, there is a magnetic
field whose
> lines of force pass from one field coil to another, because
one field
> coil is wound to produce a North pole on its inside face
and the other
> field coil is wound to produce a South pole on ITS inside
face. Such a
> dynamo at rest (but with the field coils' slight magnetism
remaining
> from the last time they were energised) has straight lines
of magnetic
> force.
> (The same principle applies to dynamos with four field
coils - like my
> NB's dynamo. I'm unsure if your J2 has two or four field
coils)
> 2. As the dynamo starts to revolve, it generates voltage;
as this
> voltage increases, current flows in the armature wires;
this in turn
> creates another, revolving, magnetic field which distorts
the field
> produced by the field coils.
> 3. This distortion does not seriously affect the output of
a dynamo
> designed to work with CVC, because the CVC is in control.
> 4. This type of distortion can be made to control the
dynamo CURRENT
> output if it can be made to REDUCE THE STRENGTH OF THE
EFFECTIVE
> MAGNETIC FIELD in the same proportion as the SPEED OF
ARMATURE ROTATION
> INCREASES.
> 5. This can be accomplished by connecting one end of the
field coil
> circuit to the positive output brush (as with the CVC
dynamo) and the
> other end to a third, movable brush connected near the
negative output
> brush in such a manner that any one segment of the armature
passes the
> third brush just before it passes the negative output brush.
> 6. As you might expect, the nearer together the two brushes
are, the
> higher the current output of the dynamo.
> 7. Note that the third brush method of control is much
better than NO
> control but it is inferior to CVC.
> This is because whether the (battery plus lights etc)
needs more or
> less
> current to maintain the correct 13.5 volts, the dynamo
doesn't know or
> care.
> If the dynamo is set to produce about 8 amps at engine
speeds above
> about 1500rpm, and your ignition coil takes 2 of these
amps, AND you
> have no lights or any other electrical load, then the
dynamo forces the
> remaining 6 amps through the ammeter and into your battery.
> This is bad if you drive 1000km at 100kmph because your
battery gets
> overcharged, hence overheated, and may well get bent plates
inside as
> well as boiling off of much of the acid.
> It is also bad if you set the third brush to produce about
4 amps AND
> you have your side & headlights on, thus taking 8 amps in
addition to
> the ignition coil's 2 amps. You will then be discharging
the battery at
> about 6 amps - let's hope you don't get caught in heavy
traffic!
>
> I haven't tried this, but I imagine that if you install a
voltmeter in
> the car, and switch resistance in and out of the field coil
circuit so
> as to keep the voltmeter indicating as near 13.5 volts as
possible, you
> would have most of the advantages of a CVC dynamo, (but
with one serious
> disadvantage if you are forgetful like me).
>
> Hope this helps.
>
> Cheers ...... Pat Mullen (1936 MG 2-seater NA0895)
>
>
> hiro@octagongarage.com wrote:
> >
> > Hi,
> >
> > We had largest MG event in Japan on Saturday 26th, and I
> > participated with my J2. The return trip was just 1000km
> > (625miles), my J2 happyly cruised around 60mph - just one
thing
> > I noticed, maybe oil pump relief valve was sticking since
> > pressure when cold become over 160LB!
> >
> > On the way to the site the third brush of my J2 dymano was
> > broken up in pieces (as you know it is very thin), then I
had
> > to purchase a spare battery.
> >
> > Does someone explain me what is the mechanism of this
type of
> > dynamo?
> >
> > Hiro
> > Kobe-Japan
> >
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