The Austin 10 is fitted with one of three variations of the A.C mechanical fuel pump mounted on the left hand side of the engine block. From November 1932 (chassis 7470) a type 'B' pump was fitted with a glass bowl, later from May 1934 onwards (chassis 42000) a type 'T' with a hand priming leaver was fitted. The type 'T' is described below.
The supply of petrol (gasoline) to the carburetter is pumped from the tank at the rear. The pump operates automatically and delivers the petrol to the carburetter in the exact quantity demanded, neither more or less an automatic mechanism accurately governs the operation.
An eccentric disc (H) on the camshaft (G) will lift rocker arm (D), which is pivoted at (E) and which pulls the pull rod (F),together
with diaphragm (A) downward against spring pressure (C), thus creating a vacuum in pump chamber (M).
Fuel from the rear tank will enter at (J) into sediment chamber (K) and through filter gauze (L) and suction valve (N) into pump chamber (M). On the return stroke, spring pressure (C) pushes diaphragm (A) upward forcing fuel from chamber (M) through pressure valve (0) and opening (P) into the carburettor. When the carburetter bowl is filled the float in the float chamber will shut off the inlet needle valve, thus creating a pressure in pump chamber (M). This pressure will hold diaphragm (A) downward against the spring pressure (C) and it will remain in this position until the carburetter requires further fuel and the needle valve opens. The rocker arm (D) is in two pieces, the outer operating the inner one by making contact at (R) and the movement of the eccentric (H) is absorbed by this " break " when fuel is not required. Spring (S) is merely for the purpose of keeping rocker arm (D) in constant contact with eccentric (H) to eliminate noise.
Virtually no regular maintenance is required with this pump, it is designed to operate without adjustment and without lubrication. Lubrication is provided automatically by oily vapour from where the pump is attached to the crank case which lubricates the linkage below the diaphragm. The only attention that is needed is an occasional clean for the gauze filter under the cover in the head of the pump. This need not be undertaken often, perhaps every 5000 miles or 2 years should be adequate.
THE PETROL PUMP WITH THE COVER REMOVED
"A" outlet union; "B" drain plug; "C" inlet union; "D" gauze filter screen; "E" cork sealing ring; "F" cover securing screw.
To clean the gauze filter, remove the top cover by undoing the securing screw. The gauze lies immediately below and can be removed for cleaning, it may be found that the gauze has stuck to the cork sealing ring, carefully pull it away taking care not to damage the gauze or seal. A little soak in a parts cleaning fluid and a careful brush over with a toothbrush will remove all accumulated contaminants from the gauze. As the main chamber of the pump is now exposed, take the opportunity to swill out any foreign matter that may be present before refitting the gauze. Locate the holes for the centre screw and the pump inlet valve correctly when replacing the gauze, also see that the top cover makes a good fit on its cork washer to avoid the possibility of leakage.
There are few moving parts in the pump apart from two automatic valves, two springs and a diaphragm, consequently, dismantling becomes an infrequent requirement. In the event of failure of any part, the replacement is easily obtained from another A.C pump of the same model from any other make/model of car except for the rocker arm that is unique to each car model. Comparable spare pumps are currently relatively easy to find and inexpensive as they were used on a huge number of cars. There are servicing specialists for A.C. petrol pumps who will be able to repair and test the pump for you.
IMPORTANT If the age of the diaphragm is unknown it is best to replace it as it may have become perished over time. In particular the old black diaphragms that were used before the wide use of unleaded petrol should be replaced, the modern additives in unleaded fuel cause damage to the diaphragm. Most suppliers of modern replacement diaphragms are supplied in red coloured material so they can easily be identified as safe for use with modern unleaded fuel.
An important point to remember is that leakage is usually only noticed when the engine is running or has just been stopped, since it is only under these conditions that the pump is primed and petrol under pressure so any leakage will then be visible. The fact that petrol may be seen to be dripping from the pump does not necessarily mean that the pump itself is at fault. First wipe the pump carefully with a rag to wipe away any petrol, operate the primer lever to make sure the pump is charged, examine closely to identify where the petrol is coming from. Check to ensure petrol is actually leaking from the pump and not simply running down the fuel line from the carburettor.
The most likely candidates for leaks are the petrol inlet and the outlet pipe unions, these must be kept tight. Possible damage to the gasket where the cover joins the pump body caused when the cover has been removed to clean the gauze. Also check the washer beneath the cover bolt head and the sediment drain plug. Sometimes the washer is missing due to it falling off as this plug is being replaced. If the cover bolt has been over-tightened, this damages the washer or in severe cases sometimes distorts the cover. It is always a good idea to replace fibre washers as once compressed they can not usually be successfully re-used. Finally check the screws around the edge of the diaphragm as they may have become loose, tightening them diagonally to ensure an even pressure.
IMPORTANT In the worse case scenario the diaphragm may be leaking at the centre where it is continually flexed, as a result petrol may be seen escaping from the small breather hole at the bottom of the pump body. If this is the case, replace the diaphragm immediately as petrol will be mixing with the main crank case oil. Once the diaphragm has been replaced an engine oil change is recommended as the oil will have been diluted by contamination with petrol.
The fuel pump is not necessarily to blame if flooding occurs at the carburettor; more often than not this is due to grit preventing the float chamber needle from seating properly (This needle controls the output of the pump to the carburettor).
PETROL SUPPLY FAILURE
TIP Should the engine stop and it is suspected that the pump is failing to supply an adequate amount of fuel to the carburettor, first check to see if there is sufficient petrol in the tank, yes really check the fuel in the tank !!. Even though the petrol gauge may indicate an adequate quantity, it is as well to make a positive check by dipping a suitable rod or stick in the petrol tank to ascertain that there is actually petrol there. Basic as this advice may appear to be, it is better to discover that you have run out of petrol BEFORE expending hours of effort dismantling things.
Now you know there is petrol in the tank, remove the float chamber bowl from the carburettor and check to see if it is full of petrol. If the level is low then petrol is not reaching the carburettor at the required rate. Place a suitable container such as a disposable paper cup under the catburettor needle valve to collect petrol. Operate the hand primer lever, it may be necessary to turn the engine half a turn, should the cam be holding down the diaphragm. A spurt of petrol should appear from the needle valve on the carburettor every time the lever is operated. Should petrol not be reaching this point it is obvious there must be a problem with the pump or fuel line.
If the pump is not providing an adequate supply of fuel to the carburettor, the cause of the trouble will probably lie in the fuel line from the petrol tank at the rear to the input on the pump. This line has a very small bore and can easily become blocked by contaminants in the fuel tank. This can usually easily be rectified by removing the fuel line at both the tank and pump ends and using a high pressure air line to blast the obstruction out. Start by applying the air to the pump end, blowing back towards the fuel tank, then repeat the procedure from the opposite end. This is an very common problem and some owners have fitted in-line fuel filters near the fuel tank to help prevent it.
If in the unlikely event that clearing the fuel line as described above does not solve the problem of inadequate fuel supply, disconnect the petrol pipe at the carburettor and operate the hand primer lever. Should petrol be reaching
this point the stoppage must be in the filter or carburettor needle valve. If still no fuel is expelled remove the carburetter fuel outlet delivery pipe union from the bottom end at the pump and try again, there might be some blockage in the pipe itself that can be cleared with an air line.
Still no petrol? It may be the pump valves that are to blame, but just before resorting to dismantling the pump check the sediment drain plug screw has not worked loose and fallen out. The consequent leak caused by a missing sediment plug would prevent the pump from working.
Now that you have tried everything else you are left with dismantling the pump as probably the valves are not seating properly due to grit. To inspect the valves, the best plan is to remove the petrol pump from the crankcase. To attempt to remove the valves without doing so is not easy and may result in damaging them. The pump is easily removed, first disconnecting the inlet and outlet delivery pipe unions and then undoing the two nuts securing the pump to the crankcase. The pump can now be taken to the bench and the inlet and outlet valves removed. These are just under the gauze; they can both be easily removed. The valve springs and the valves may be emptied out into the palm of the hand, being careful not to mix them up; the outlet valve spring locates round the stem of the valve and round the short stem on the inside of the valve plug.
Examine the valves and their seatings and see that foreign matter is not preventing the valves from seating properly.
If either valve is damaged, replace with a new one and clean the seatings before fitting. When replacing the outlet valve plug, ensure that its stem locates in the coils of the valve spring which has previously been replaced on top of the valve. The same applies to the inlet valve except that its spring is beneath the actual valve plate. It is important that the fibre washers under the heads of both valve plugs are not omitted on reassembly and also ensure that both plugs are tight home. There is also a fibre washer under the head of the top cover screw. The linkage operating the diaphragm will not require attention and in nearly every case the only necessary attention to the pump will be a cursory examination of the gauze filter under the
1. Top cover screw. 2. Cover screw washer. 3. Pump top cover. 4. Cover cork washer. 5. Filter gauze. 6. Upper chamber. 7. Drain plug joint washer. 8. Drain plug washer. 9. Drain plug. 10. Spring retainer. 11. Valve spring. 12. Valves. 13. Valve plate washer. 14. Valve retainer plate. 15. Valve plate screw. 16. Priming lever spring. 17. Lower casting. 18. Rocker arm stop screw. 19. Stop screw washer. 20. Rocker arm pin. 21. Rocker pin washers. 22. Rocker arm pin clips. 23. Rocker arm. 24. Rocker lever spring. 25. Rocker link. 26. Diaphragm spring. 27. Diaphragm and pull rod.