Electrical issues found when fitting a larger engine in a 1.0
HISTORY
the 1.0 ohv engine is a throwback to the 1960's. all the ignition components are old fashioned.
the ignition setup is still of a contact breaker type, made by bosch, and simply can't cope with large voltage.
to solve this, the bosch people came up with a clever solution. if 12v will kill it, then lets use 6v. so the coil is a 6v rated item, and to make this work on a 12v system, they fitted a 'ballast resistor' of the same resistance as the coil's LT windings, to fiddle it as 6v.
then there is a problem with starting. as in when the battery is being drained upon cranking, the voltage drops to the coil & gives a very weak spark. so they fitted a switched live from the starter solenoid to the coil, so when it cranks over, a higher voltage is supplied to the coil.
this system has not been fitted to any other nova models (for the pedants, the euro spec corsa a 1200 ohv is pretty much identical to the 1.0 nova, but never sold over here, thank god)
PROBLEMS
when fitting a different engine the following problems occur.
1. the 'ballast' wire from the ign switch to the coil will not supply 12v, so needs swapping for an ordinary 1mm2 copper wire, then the correct voltage is supplied to the new coil, or in the case of injection engines, the ecu loom. to do this, you need to trace it right back to the ign switch & remove as much of it as you can before connecting in the new wire. use BLACK if you can, as its the gm switched live colour
2. there will be a spare wire that was connected from the starter solenoid to the coil. it is .75mm2 black. it needs removing. so it does not short out, or get accidentally connected to the wrong thing & burn out.
Other things of note.
the ohv gauge sender wires will be the wrong length for the ohc engines, but will be of the correct type & colour, they might need extending or shortening to suit.
be careful with the alternator wiring, as this seems to cause frequent problems
they are
large red (4mm2) from the starter goes to B+
small blue/white (0.75mm2) is the charge wire, goes to D+
the large brown (4mm2) is the earth, goes to B- and needs connecting to the engine block.
