The Fordson Tractor Pages Forum

My big question is about the resistor or ballast resistor. Does a petrol dexta fire with 6V or 12V? and is there a right or a wrong way of wiring the resistor? Currently I have 12V input and 6V output at the resistor than a wire to the coil and from the coil to the distributer... however i found that the resistor was getting quite HOT. thanks for the help.

I cant comment on the petrol dexta but, the wiring of these on most ignition systems of that type is that they are connected as you describe.

Quite often the resistor is bypassed by a wire from the start position of the ignition switch or the start button to increase the volts to the coil whilst the battery is under load from the starter during cranking.

And yes, they do get pretty hot (but do check your dwell on the points, if set to long then they get hotter)

The petrol Dexta is 12 Volt with a 12 Volt coil which does not require a ballast resistor. I use the coil from a TE20 Ferguson, I have just had to fit a new one on mine as the original coil started to blow the capacitors after about an hours running. Got through my complete stock of spare capacitors in a days running before finding the faulty coil.

Like Brian's mine is 12 volt with no resistor. Can't see the point in fitting a 6v ballast setup as they start so easy anyway. Just another thing to go wrong.

so i can just forget about the resistor ? 12V straight to the coil and it wont damage the points or capicitor. Originally were these tractors 6v? i thought i read that before

The petrol Dexta has never been 6 volt, the early tractors like the 9N and other US Fords up to the 1960's were but the petrol Dexta is a British tractor. We moved to 12 volt electrics during the 1940's.

brian
how do u know a capacitors blown ? simply no spark ??

Yellowish/Whiteish spark and blackened cratered points. Tractor also runs as if short of fuel and may only run on one or two cylinders.

thanx

what is the name to indentify the fordson petrol engine? massey has the same one too and i know the diesels are made by perkins but never knew who made the gas

for the petrol 1964 do people have negative to ground or positive?

The manual says all Dexta's are positive earth.

The petrol Dexta engine is a Standard Motor Company Industrial engine. It is similar to the engine in the Petrol MF 35 and TE-20 also the Standard Vanguard and Standard Triumph sports cars but it is not the same as any of them. Two cases in point are the starter position and the valves. The Petrol Dexta has two different sizes of valve stem, the inlet is the same as a TE-20 the exhaust is from a Triumph sports car.

The engine was used as a power unit on a Massey 701 baler and in generators and water pumps.

Petrol tractors, like Dextas, Super Dextas and all the Major range were all Positive earthed as were most cars and lorries of the time. It does not matter whether they are Negative or Positive earthed, the lights still shine and the starter works in the right direction BUT the dynamo must be polarised to the correct earthing.

With the dynamo mounted but without the leads connected, take a wire from the output terminal of the battery, be it Positive or Negative and touch the Field Terminal (small one) on the dynamo. Job done. Reconnect wires to dynamo. This should be done every time you fit a new or second hand dynamo. If you do not do it you stand a good chance of burning your tractor and shed down. I have seen this done on at least two occasions when fitting a wrongly polarised dynamo caused major fires.

great description thank you

islander wrote:what is the name to indentify the fordson petrol engine? massey has the same one too and i know the diesels are made by perkins but never knew who made the gas

IIRC, didn't someone write something about the origins of the Dexta diesel engine
Best described as "Perkins designed" but Ford cast block and head in Dagenham, with final machining and assembly by Perkins, to Ford specifications.

The Petrol Dexta SHOULD have had a Perkins petrol engine based on the diesel Dexta. Perkins could not get it developed in time though. Eventually the Perkins Petrol was used in the US in the MF 135 so I understand. Have not seen one but would like to.