Tachometer Question

[brassringfarm]

All--The plastic piece on the back of my tach (Elan S2 - Inductance Tach)
where the two loops of wire gores through was missing. I've machined a new
one out of nylon - but the literature I have shows a "U" shaped piece of
metal going over the plastic with tabs going into the body of the tach
itself. Since the plastic (and metal piece) are held down by a knurled nut
(Which I have)--what purpose does the metal serve? Do I need it? Does it help
to concentrate the inductance field so the coil, etc can trigger?
If I do need it - is it just a pressure fit down into the slots in the tach?
Thanks in advance
Paul
***@***.***

[Rob_LaMoreaux]

The loop and all on my induction type tach is internal to the tach so I can't say for sure what your should be like, but electrically looping the wires around a nylon piece won't do much. I am sure the usuall plastic piece onthe back contains windings of thin magnet wire to form and transformer when the iginition wire is looped through the center. Without these wires you won't get pulses to the transistor that forms the intergrator part of the tach.

Could this be an internal pickup inductive tach?

Rob LaMoreaux
Ann Arbor, MI USA
(734)-971-5583
***@***.***
Too many Hobbies.... Too Little Time
1969 Lotus Elan....It's not a restoration, it's a never-ending
adventure.

[saarhus]

Paul

All--The plastic piece on the back of my tach (Elan S2 - Inductance Tach)
where the two loops of wire gores through was missing. I've machined a new
one out of nylon - but the literature I have shows a "U" shaped piece of
metal going over the plastic with tabs going into the body of the tach
itself. Since the plastic (and metal piece) are held down by a knurled nut
(Which I have)--what purpose does the metal serve?

The metal loop is the conductor for the pulse that is generated in the
loop when the points open/close.

Do I need it?

Yes!

Does it help to concentrate the inductance field so the coil, etc can
trigger?

It provides the electrical and physical contact with the corresponding
contacts in the back of the tach.

If I do need it - is it just a pressure fit down into the slots in the tach?

The ends of each leg of the metal loop are intended to make contact with the
two recepticals in the connector on the back of the tach.

Thanks in advance
Paul

[rodney]

Paul

The metal(steel) u is essential, it forms the MAGNETIC circuit for the
pulse, without it there is no transformer action. You should be able to
make one out of a thin piece of steel plate. The ends that go into the
tacho slide in next to the other half of the magnetic loop.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: ***@***.***lto:***@***.***
Sent: Saturday, 10 November 2001 11:52 AM
To: ***@***.***
Subject: [LotusElan.net] Tachometer Question


All--The plastic piece on the back of my tach (Elan S2 - Inductance Tach)
where the two loops of wire gores through was missing. I've machined a new
one out of nylon - but the literature I have shows a "U" shaped piece of
metal going over the plastic with tabs going into the body of the tach
itself. Since the plastic (and metal piece) are held down by a knurled nut
(Which I have)--what purpose does the metal serve? Do I need it? Does it
help
to concentrate the inductance field so the coil, etc can trigger?
If I do need it - is it just a pressure fit down into the slots in the tach?
Thanks in advance
Paul
***@***.***










reserved.

[Elan45]

Paul,

Yes, you need it. It's what makes the electrical contact. I've made them before out of thin brass sheet, maybe .025 to .032" as they seem to be easilylost.

Roger


here the two loops of wire gores through was missing. I've machined a newo
ne out of nylon - but the literature I have shows a "U" shaped piece of
metal going over the plastic with tabs going into the body of the tach
itself. Since the plastic (and metal piece) are held down by a knurled nut(
Which I have)--what purpose does the metal serve? Do I need it? Does it help
to concentrate the inductance field so the coil, etc can trigger?
If I do need it - is it just a pressure fit down into the slots in the tach?
Thanks in advance
Paul
***@***.***

[Elan45]

Pretty sure originals are plated brass and therefore non magnetic.

Roger



The metal(steel) u is essential, it forms the MAGNETIC circuit for the
pulse, without it there is no transformer action. You should be able to
make one out of a thin piece of steel plate. The ends that go into the
tacho slide in next to the other half of the magnetic loop.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: ***@***.***lto:***@***.***
Sent: Saturday, 10 November 2001 11:52 AM
To: ***@***.***
Subject: [LotusElan.net] Tachometer Question


All--The plastic piece on the back of my tach (Elan S2 - Inductance Tach)
where the two loops of wire gores through was missing. I've machined a new
one out of nylon - but the literature I have shows a "U" shaped piece of
metal going over the plastic with tabs going into the body of the tach
itself. Since the plastic (and metal piece) are held down by a knurled nut
(Which I have)--what purpose does the metal serve? Do I need it? Does it
help
to concentrate the inductance field so the coil, etc can trigger?
If I do need it - is it just a pressure fit down into the slots in the tach?
Thanks in advance
Paul
***@***.***










reserved.

[saarhus]

Roger and all,

Just buffed the surface crud off my original U clip, and the metal is
definitely steel.

----- Original Message -----
From: "Roger Sieling" <***@***.***>

Sent: Monday, November 12, 2001 8:39 AM
Subject: RE: [LotusElan.net] Tachometer Question


Pretty sure originals are plated brass and therefore non magnetic.

Roger

[rodney]

Roger

I will have to check 99.9% sure though. How can a single piece of metal be
an electrical contact when it makes no contact with any wire in the plastic,
or the wire from the ignition. The coil that picks up the pulse is internal
to the tacho, at least is was on mine.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Roger Sieling [mailto:***@***.***

Pretty sure originals are plated brass and therefore non magnetic.

Roger

[rodney]

Stan

I am sure it was on mine. I have actually replaced it with a voltage type
many years ago when I installed a transistor assisted ignition.

I cannot see how Rogers brass one worked, unless it was brass plated steel,
it does supply the magnetic circuit, not the electrical connection.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Stan Aarhus [mailto:***@***.***
Sent: Tuesday, 13 November 2001 2:26 AM
To: ***@***.***
Subject: Re: [LotusElan.net] Tachometer Question


Roger and all,

Just buffed the surface crud off my original U clip, and the metal is
definitely steel.

[Elan45]

Rod,

You have a Series 4. Earlier cars used an external loop through a plasticpiece contained within a metal "staple", which its two ends penetrate the back of the tach making contact with two separate socket contacts. The loop's inductance causes a current in the "staple". The loop must also be looped just a certain direction too. I don't understand how the plastic piece wouldhave been gone, since it is part of the ignition wire.

Roger



I will have to check 99.9% sure though. How can a single piece of metal be
an electrical contact when it makes no contact with any wire in the plastic,
or the wire from the ignition. The coil that picks up the pulse is internal
to the tacho, at least is was on mine.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Roger Sieling [mailto:***@***.***

Pretty sure originals are plated brass and therefore non magnetic.

Roger

[Elan45]

These tachos were a common improvement to cars like MGA and early AH Sprites. Almost every Sprite I knew of in the 70s had a broken tach drive gearbox. This was a common update for most of my racing friends when we were not much more than college students and you were lucky to have an engine that would rev to 7 grand. Many were removed from breaker's yards minus both the "staple" and the plastic loop holder, so we had to improvise. But it's been better part of 30 years. Maybe I have forgotten what I made it from. My concern with a steel piece would be corrosion with the contacts.

Roger



I am sure it was on mine. I have actually replaced it with a voltage type
many years ago when I installed a transistor assisted ignition.

I cannot see how Rogers brass one worked, unless it was brass plated steel,
it does supply the magnetic circuit, not the electrical connection.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Stan Aarhus [mailto:***@***.***
Sent: Tuesday, 13 November 2001 2:26 AM
To: ***@***.***
Subject: Re: [LotusElan.net] Tachometer Question


Roger and all,

Just buffed the surface crud off my original U clip, and the metal is
definitely steel.

[rodney]

Roger

I don't have an S4, I have a 1967 S3 SS.

A coil of wire induces a voltage in another coil of wire by the changes in
the magnetic flux passing through the second coil. A wire passing through a
coil at rightangles is not a very effective method of transfering this field
as it is in line with the field. I will try a simple diagram.

-------( ||||| )
) ||||| (-------
( ||||| )
) ||||| (-------
-------( ||||| )
Input Steel Output
Coil /Iron Coil

This is a simple transformer/igniton coil type where two coils a wound
parallel to each other around a core of magnetic material at rightangles to
the coil of wire with no electrical contact between either coil. A changing
(and it must be changing) current in one coil induces a voltage in the other
coil by the changing magnetic field at a value that depends on the ratio of
the windings in the two coils and the applied voltage. In our tacho circuit
we have a small number of turns (loop of wire) with a high current/low
voltage that needs to be converted into a low current high voltage which
requires a greater number of turns, the single metal loop is only one turn.

I hope this isn't too confusing as I am trying to simplify it as much as
possible.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Roger Sieling [mailto:***@***.***
Sent: Tuesday, 13 November 2001 8:07 AM
To: ***@***.***
Subject: RE: [LotusElan.net] Tachometer Question


Rod,

You have a Series 4. Earlier cars used an external loop through a
plasticpiece contained within a metal "staple", which its two ends penetrate
the back of the tach making contact with two separate socket contacts. The
loop's inductance causes a current in the "staple". The loop must also be
looped just a certain direction too. I don't understand how the plastic
piece would have been gone, since it is part of the ignition wire.

Roger



I will have to check 99.9% sure though. How can a single piece of metal be
an electrical contact when it makes no contact with any wire in the plastic,
or the wire from the ignition. The coil that picks up the pulse is internal
to the tacho, at least is was on mine.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Roger Sieling [mailto:***@***.***

Pretty sure originals are plated brass and therefore non magnetic.

Roger







reserved.
















reserved.

[brassringfarm]

Well - Thanks to everyone's help - the Inductance Tach works great, as of last night. I 'fabricated' the metal piece that goes over the external nylon block out of some galvanized steel sheet I had (it took about 3 minutes) and forced it a few millimeters down into the exposed slots in the back of the tach case. Ran a hot wire from Ignition switch post 2 to the main tach connection. Ran another in parallel from post 2, creating a loop in the external nylon block and then on to the negative side of the coil. Grounded the tach case at the clamping posts.
Worked like a champ! Now I can do other fun things--like really tune the carbs.
Next - to get the frozen speedometer working! How do you get the blasted thing out of the case? Do you have to take off the front of the dial first - so you can remove the trip odometer rod?
It's an adventure!
Thanks again everyone.
Paul

[paul_adamson]

Yikes! I vaguely remember disassembling my speedometer.
Not pleasant.
I removed the bezel and glass first.
The trip-reset rod has a tiny scroll pin holding it on ? that I do remember.
I managed to get the thing apart but I didn?t succeed in getting the reset
rod back.
Maybe another list member can be of more help.
Thinking about it, you are probably meant to remove the face and needle but
I didn?t fancy that at the time.

Perseverance must be the key. If you do work it out, please let me know!


-----Original Message-----
From: ***@***.***lto:***@***.***
Sent: 13 November 2001 15:11
To: ***@***.***
Subject: [LotusElan.net] The Tachometer Lives!---Next--the speedo
<SNIP>
Next - to get the frozen speedometer working! How do you get the blasted
thing out of the case? Do you have to take off the front of the dial first -
so you can remove the trip odometer rod?
It's an adventure!
Thanks again everyone.
Paul

[rodney]

Paul and Paul

Your memory is correct.

The bezel has to be removed, this may entail lifting the tabs on the back of
the bezel slightly. You then rotate the bezel until the tabs line up with
the slots in the back of the case. This is usually hampered by the perished
rubber gasket gluing the bezel/glass/case together. After the bezel the
glass is removed then the needle. The needle shaft is very delicate and
there is a special tool made to remove then, BUT you should be able to prise
it off if you are careful. Then you undo the two screws holding the scale
plate. After that you will have access to the internals, from that point on
it is all up to your expertise on instrument repair.

Rod

Rodney Stevens
CSIRO Minerals
http://www.minerals.csiro.au

Ph. 61 2 97106701
Fax 61 2 97106789

Personal Home Page
http://sites.netscape.net/rodjohnstevens

-----Original Message-----
From: Paul Adamson [mailto:***@***.***
Sent: Wednesday, 14 November 2001 6:58 AM
To: ***@***.***
Subject: RE: [LotusElan.net] The Tachometer Lives!---Next--the speedo


Yikes! I vaguely remember disassembling my speedometer.
Not pleasant.
I removed the bezel and glass first.
The trip-reset rod has a tiny scroll pin holding it on - that I do remember.
I managed to get the thing apart but I didn't succeed in getting the reset
rod back.
Maybe another list member can be of more help.
Thinking about it, you are probably meant to remove the face and needle but
I didn't fancy that at the time.

Perseverance must be the key. If you do work it out, please let me know!


-----Original Message-----
From: ***@***.***lto:***@***.***
Sent: 13 November 2001 15:11
To: ***@***.***
Subject: [LotusElan.net] The Tachometer Lives!---Next--the speedo
<SNIP>
Next - to get the frozen speedometer working! How do you get the blasted
thing out of the case? Do you have to take off the front of the dial first -
so you can remove the trip odometer rod?
It's an adventure!
Thanks again everyone.
Paul












reserved.