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Technical Pages - ELECTRICAL

Getting Your Spark Advanced - (taken from Capital Minors, January 2000)

The Lucas distributor used on the Morris Minor overhead valve engine is a very carefully calibrated piece of mechanism and as such must be kept in good operating condition to ensure the best performance from the engine There are two ignition control governors that regulate the time of firing the spark plugs according to engine speed and load.
The vacuum governor which is connected to the carburettor by the small diameter pipe, advances the ignition rapidly at low revs on initial take off from rest.

The instant the throttle is opened above idle speed, suction from the increased RPM will pull the diaphragm of the governor against a spring and rotate the points holding plate in the distributor in the advanced direction.
This will give the engine the power to pull away at low speed. As the engine revolutions build up and the initial load of getting the mass moving decreases, so the vacuum reduces and the diaphragm is pressed back by the spring. However, at the same time the increase in revolutions causes the second mechanical governor built into the base of the distributor to commence to throw out its bob weights and advance the cam to overcome the now falling off of vacuum advance. As speed increases, the vacuum drops away overcome by the return spring, but the engine is kept in an advanced spark condition according to the engine revolutions by the mechanical governor.

The spark is set at idle speed up to 600 RPM when all systems are at rest according to the degree of time at 5 to 8 degrees before top dead centre. (TDC) This setting is standard for a smooth idle, but not sufficient advance to get any power for driving and will advance the spark to 14 to 17 degrees via the two governors for ideal performance as speed increases, If either of these two governors are not working, then the car will be sluggish on acceleration and have little power on hills and will run hot and consequentially bum valves continuously.

To check the function, first remove the distributor cap, then disconnect the vacuum pipe line at the carburettor end. Add a length of small bore close fitting rubber hose tubing to the pipe line and suck on the hose, at the same time observing the rotational movement of the distributor points mounting plate. When you suck, the vacuum governor will pull the plate in the advance direction and it will snap back when the sucking stops. If, when sucking, you can not build up any suction, then the system can not work and there is a leak somewhere, ether in the pipe line or the governor diaphragm is punctured. Renew.

The mechanical flyweight governor is beneath the points plate, so it is necessary to dismantle the distributor to view this governor. However, if you remove the rotor button you will see a screw underneath it in the centre of the cam shaft. This is where a drop of oil is necessary every 4-5000 miles to keep the governor shaft free. Refit the rotor and thrust it back and forth in a rotary action and feel if the cam is free on the centre shaft and you can hear the bob weights clicking.

If it is seized solid then the distributor must be removed and overhauled. Until all this mechanism works correctly you are wasting time trying to time the engine and can cause damage to the engine.

If somebody else's Morris Minor goes better than yours, this is probably why. The engine is running retarded.

How to make the self cancelling device on the indicators work.

Since I have had 61MORI this has not worked and I thought it was just worn and I would fix it " some day ". Well the day arrived because I failed a warrant when there was too much up and down movement in the steering column and also free movement as the steering wheel was rotated.

All this was traced to the clamp at the bottom of the steering column which needed the slot to be widened so it clamped tightly. However when I reassembled ( which involved setting up the steering wheel so the spokes were in the correct position) the self cancelling still did not work.

A chance remark from Jeff Attwood told me what was wrong. The slot in the steering wheel clamp must be at the bottom of the steering column when the wheels are straight ahead. This allows the pin that actuates the self cancelling device to trip the mechanism when the wheels return to the straight ahead position. All very simple. It then remained to remove the horn button, remove the steering wheel nut and remove the steering wheel ( which is splined ) and adjust the position so the spokes are correctly aligned for straight ahead.