2T – Double Trouble ????
Introduction
Witness the scene at the start of a Club outing
when the riders of 2T powered machines prepare to start. Kick – Whrr – Silence:
Kick – Whrr – Silence. The sequence is repeated numerous times until eventually
they are rewarded with the sound Kick –
Whrr – Dm – Dmm – Dmmm – Vroom as the engine comes to life and starts to fire
on both cylinders. At this point I should offer my apologies to 2T
riders/owners. I promise I am not taking the proverbial P*** - just trying to
convey in words what I have observed.
So
what might be the cause of the reluctance of the engine to fire up after a
couple of prods? Well, assuming that the engine is in good mechanical condition and the carburation is as specified by
Villiers, suspicion naturally falls on the electrics. This article looks at 2T
electrics and was prompted when the Greeves 25DB owned by Ron Lewis exhibited
the symptoms described above. Ron found that by converting the Greeves to
battery/coil ignition he solved his starting problems, and as a bonus found
that the performance of the bike was greatly improved. The only problem with
his arrangement was that the battery was not being charged. Together we
designed and installed a system to overcome this problem, and thought that
other 2T owners might like to know of our experience.
The Conventional 2T Ignition System – energy
transfer
Before
delving into the complexities of a modification to provide a permanent
battery/coil ignition system on the 2T, I believe it would be of use to
consider the original system employed by Villiers.. Essentially the system
works on the “energy transfer principle”. Internally the magneto has two Low
Tension (LT) ignition source coils. These coils are connected to two Contact
Breakers (CB) shunted by capacitors. When closed a CB will conduct the
electrical energy being generated by an LT ignition source to earth. At or near
the point of maximum energy generation by the LT ignition source coil the CB is
opened by the ignition timing cam. The energy being generated in the LT
ignition source coil is immediately transferred to the primary of the High Tension (HT) ignition coil. This
energy is then stepped up by
transformer action to a high voltage which is sufficient for a spark to
jump across the spark plug points. Because the energy in the LT ignition
source coil is transferred to the HT ignition coil when the CB points
open, the system is termed energy transfer. Note the essential difference between the systems – in the energy
transfer system the CB is in parallel with the HT ignition coil primary whereas
in a conventional coil ignition system the CB is connected in series with the
HT ignition coil primary.
The obvious advantage of the energy transfer
system is that a reasonable High Tension spark plug voltage can be generated
without the need for a battery. However the level of voltage generated (and
hence starting performance) is
essentially dictated by two main factors:
1
The speed of rotation of the engine/magneto,
where the higher the engine speed the higher the voltage which is generated (up to a finite maximum)
2
The CB must open at the time of maximum energy
generation in the LT ignition source coil
Point
1 above reveals a potential reason for poor starting. When kick starting an
engine the rpm is at its lowest, hence
the spark voltage generated by energy transfer is also low resulting in
a “weak” spark.
Point 2 essentially means that ignition timing
is very critical. The CB must be kept in good condition and Manufacturers
recommendations on timing and CB gap must be followed closely to obtain and
maintain correct operation of the system. A small error in the CB setting is
more serious in the energy transfer system than in a conventional battery/coil
system. Note also that the 2T Workshop Manual recommends that the ignition
timing should be set with the cylinder heads and gaskets removed.
In
addition the electrical wiring between
the LT ignition source coil and the HT ignition coil primary should be in good
condition. Ideally a single wire in which there are no electrical connections
(other than the terminations) is desirable. Additionally the HT lead from the
HT ignition coil should be clean, electrically sound and with good electrical
connections to the coil and plug. (If in doubt replace it with a new silicone
rubber lead and spark plug cap) It goes without saying that the correct type of
plug, gapped in accordance with Manufacturers recommendations must be used.
However over a period of time there are other factors which can affect the
electrical output of the system. These are ;
·
The magneto may lose some of its magnetism
·
Coils (both LT ignition source and HT ignition
may develop internal short-circuits as insulation deteriorates
·
Electrical terminations (including earth
connections) may start to corrode and effectively impose a resistance to
electrical current
So
if you experience 2T starting problems and suspect the electrical system, it
would be worthwhile checking out the system for possible sources of trouble as
described above. If you remain dissatisfied with the system, then a conversion
to a battery/coil ignition system is worth considering.
The
advantages of the battery/coil ignition system over the energy transfer system
are:
·
Maximum spark voltage is obtained at low rpm
for starting purposes and remains reasonably consistent at normal running
engine speed.
·
Ignition timing and CB gap are less critical.
Obviously
the installation of a battery/coil system will not rectify other possible
electrical defects mentioned in the discussion of the energy transfer system.
The system should therefore be fully checked for any potential deficiencies,
including checks on and CB gap, to ensure that the benefits of a battery/coil
system are realised.
The
original Lucas and Miller electrical diagrams from the 2T Workshop Manual were
used as the basis for the conversion to battery/coil ignition.. It should be noted
however that some motorcycle manufacturers may not have employed the same
colours of wires when assembling their machines.
All
the existing components (with the exception of the old rectifier) are retained,
but rewired to meet the demands of the new system. The only additional
components required are (1) two new
solid state full-wave rectifiers, (2) an ignition switch and (3) electrical
wiring of at least 7 amp rating. While the original HT ignition coils could be
retained, replacement of these items by new HT ignition coils designed for coil
ignition is recommended, particularly if starting has been a problem.
Essentially
the modification requires some changes to be made to the connections of the LT
ignition source and lighting coils located within the magneto. The resulting AC
outputs from these coils are converted to DC by full-wave rectification. In
daylight running the output from the LT ignition source coils is sufficient to
provide enough power for coil ignition and a trickle charge to the battery.
When the headlight is switched ON the additional power requirement is satisfied
by the rectified output from the lighting coils. Should you wish to include it
in your installation, I have shown a “Charge Boost Switch” in the diagram. The
effect of this will be to provide a higher battery charging current during
daytime running (ie with headlight OFF) should you need to give the battery a
boost.
Note
however that prolonged running in this condition is likely to cause battery
overcharge with significant loss of electrolyte. The modification also includes
provision for Emergency Starting in the event of a flat battery. By switching
to Emergency the battery is disconnected and the full rectified output of both
the LT ignition source coil and Lighting coils are used to supply power direct
to the HT ignition coils.
The
modification to the Lucas system and the Miller system are described. the only
difference to the modification for the Miller system is in the connections to
the Lighting switch. In both systems the wiring arrangements for the Headlight,
Tail light, Pilot/Park light, Speedo light, Horn and Stop light remain
unaltered from the original system. Additionally the new system can be operated
on the existing 6 wires which connect the engines electrics to the frame, thus
retaining the original electrical connector. Note that where an ammeter is
fitted, the supply for the Horn and Stop light should be taken direct from the
battery and not routed through this instrument. Additionally, although it is common
for the Horn button to be incorporated in the Dip switch, for convenience in
the diagrams it is shown as a separate item.
The changes which are necessary are summarised
below. Access must be gained to the Armature plate on which is mounted the Lighting coils and the LT ignition
source coils. Wiring changes are required for both sets of coils.
Lighting
Coils : The two lighting coils must be connected in parallel. This is achieved
by disconnecting the Purple (Mauve) wire from the lower coil. Using a length of
new wire, connect the coil terminal from which the Purple wire has been removed
to the terminal on the upper coil to which is attached the Red wire. Remove the
Yellow wire from the centre tap on the upper coil. The Black wire remains in
the original position, but check that there is a connection from this terminal
to the lower coil. The full AC output from the lighting coils is now obtained
from the Red and Black wires.
LT
ignition source coils : Both LT ignition source coils must be also connected in
parallel. This is achieved as follows :
* Disconnect and remove the
links from both coils to the snap connectors connected to the Contact Breakers.
* Remove the earth connection
from both coils.
* ` Using lengths of new wire
connect coils E1 and E2 in parallel insulating as necessary and using good
solder joints.
* Connect the Purple wire
previously connected to the lower lighting coil to the top terminal on the coil
E1.
* Connect the Yellow wire
previously connected to the top lighting coil to the bottom terminal on the
coil E2.
The
full AC output from the LT ignition source coils is now obtained from the
Purple and Yellow wires.
Make
the following disconnections:
Lucas
System
*# Disconnect the Green wire
which runs from the original rectifier to Terminal 1 on the Lighting switch
*# Disconnect the Red and Black
wires from the original rectifier.
* Remove and discard the
original rectifier.
*# Disconnect the Purple wire
from the LH Lever of the Lighting switch.
*# Disconnect the Yellow wire
from Terminal 3 of the Lighting switch
* Remove the earth connection
from both HT ignition coils.
Miller
System
*# Disconnect the Red wire which
runs from Lighting switch Terminal 2 to the engine electrical connector at the
engine end ONLY.
*# Disconnect the Purple (Mauve)
wire from Terminal 3 of the Lighting switch.
*# Disconnect the Yellow wire
from Terminal 1 of the Lighting switch
* Remove the earth connection
from both HT ignition coils.
Leave
these wires (#) in position as they will be reused in the new system.
Now
for the reconnections. These are reasonably straightforward. Mount the solid
state rectifiers on a bracket which will provide a sufficiently good heat sink
and connect it to the frame. A suitable location may be under the seat. Using
suitable electrical terminations, connect the Red and Black wires to the AC
terminals on one of the rectifiers. You will note that I have given the system
a negative Earth to bring the installation in line with modern practice.
To achieve this configuration connect the negative terminal of the rectifier to
earth (if you wish to retain the positive earth system , then the
positive rectifier terminal should be connected to earth). Again, using
suitable terminations connect the Purple and Yellow wires to the AC terminals
on the second rectifier, and the negative to earth. Lengths of new wire should
be used to connect the positive terminals of both rectifiers to the new
Ignition On/Off/Emg switch. In the Lucas system, (depending on wire
routing and ignition switch location), it should be possible to use the
existing Green wire to make the connection between the new Ignition switch and
the Lighting switch LH Lever. In the Miller system the Red wire (which was left
connected to Lighting switch Terminal 2) can be used to provide the connection
to the new Ignition switch. Note there is a new link required on the
Lighting switch. In both systems, Lighting switch Terminal 1 should be linked
with a length of new wire to Terminal 3.
Using
a length of new wire connect the +ve terminal of the HT Ignition coils to the
new Ignition switch. Note the linkages which are also required on the Ignition
switch. The HT Ignition coils should be connected to the Contact Breakers using
the existing Blue and Green wires. Take care to ensure that the Contact breaker
for a specific cylinder is connected to the correct HT ignition coil. An
Ignition Warning light in circuit will glow while the Ignition is ON and is
recommended as a visual indication of the Ignition status. With these
connections the modification is essentially complete, but make sure the
Battery negative has been connected to earth if this configuration is being
adopted.
Villiers
diagrams show an ammeter in circuit. This need not be a permanent part
of the installation, but it is essential for test purposes. Testing basically
consists of running the engine and checking on the amount of current being
delivered from the generator. When the engine is running at a speed which
approximates to 25 – 30mph with lights OFF the ammeter should register a small
charge (about half amp) Note that at tickover it will register a
discharge. With the headlamp switched ON the ammeter should again register a
small charging current consistent with
a reasonable road speed. Once confidence has been gained in the system, by
taking the machine on a reasonably long run, the ammeter may be removed and
replaced by a wire link.
In
conclusion, while this article concentrates on the changes we made to our 2T
engine, the principle could equally be adopted for single cylinder engines.
Best
wishes and happy 2T-ing Bill
Drummond