Every 2000 miles (3200km) the engine oil should be changed. Every 250 miles (400km) the oil level should be checked/topped up. Original oil specified was a mono-grade SAE 30, or for hotter climates (over 90 deg. F./32 deg. C.) an SAE 40. It cannot be stressed too strongly that modern high detergent oils, and especially multigrades, should not be used in an old design of engine. Tales of woe, and sometimes catastrophic disaster (!) in old engines generally, are often traced back to incorrect oil. It is worse still if a change to modern oil is done on an engine that has not recently been rebuilt. Accumulated sludge may be dislodged and then block oilways. Even in a clean 'new' engine, oil consumption may increase, and piston-rings might stick/break.
Ignore any claims that the above warnings are myths. All those in the world of preserved transport who learned the hard way, did not imagine their problems/disasters. I've experienced it, know others who have, and know overhaul engineers with a lifetime in marine/railway/car engine work, who have dealt with the consequences. Risks of major disasters diminish if your engine has been converted to full-flow oil filtering (not bypass oil filtering). But the ancient AC design also lacks good air filtering and has the larger running clearances found in 'vintage' engines. Less air filtering means more sludge. Larger clearances, and high relative surface velocities (within bearing surfaces) can affect the performance of multigrade oil, reducing its effective viscosity. That can also cause increased oil consumption. Another possible risk is oil drainage off the engine parts while switched off and standing for a while. This tends to be worse with multigrades, although it depends on the particular oil used. Synthetic oils might work very well, but would still need to be changed at short intervals, which defeats their biggest benefit - long life.
The AC engine was not originally fitted with a full-flow oil filter. There is a gauze filter to try to prevent any large debris from entering the oilways, but this has nothing to do with removing the fine metal dust that a modern filter deals with. Later engines (from about 1951/52) had a Fram by-pass filter mounted on the exhaust manifold. I believe that its element should be renewed every 10000 miles (16000km). Replacement filter element was the Fram C3, or equivalent such as Greyfriars 530P.
Some engines have since had full-flow filters installed, but it is important that the flow of oil has not been impaired by this modification. It is open to question whether this mod. will allow an increase in mileage between oil changes. Oil life is also influenced by contamination by acid and water, plus the amount of dust drawn in passed the (rather primitive) air-filters. If a conversion to full-flow filter is planned, then it is best to get one that includes the pressure relief valve. Remote filter/valve units are available although I have not tried any myself.
Engine (Cooling System)
The AC's cooling system is not pressurised, therefore it runs at a cooler temperature than more modern systems, that is, around 75 deg. C. A certain amount of coolant is lost via the radiator overflow pipe, and so it needs regular checking and topping up. The alloy engine castings are prone to corrosion, and so an anti-freeze with corrosion inhibitor should be in use all year round. Coolant capacity is 17 pints (9.6 litres).
The water-pump design is definitely not the best part of an otherwise superb engine! The pulley is forward of the ball-race bearing, and this effectively places some extra load on the plain bearing at the rear of the spindle, and increases its wear rate. The water seal is a carbon gland, which to some extent relies upon centrifugal force to keep the water from escaping. For that reason, leakage will be greatest at low revs. If rebuilding a pump, the carbon gland needs quite a bit of bedding in before it seals well. This can be done on a workbench using an electric drill. Many owners have tried modifications to improve the design, but I don't have details of any of the successful ones. As an added precaution, I used to carry a short fan-belt in the car, which can be used to drive the fan, but not the pump, just in case the pump bearing fails (through water leakage). Reconditioned pumps are now available from AC engine specialists. See the links page.
The thermostat is of the bellows type. Over time/usage, it will tend to open at too low a temperature, or else stay open. Assuming that the bellows are not leaking, I understand that it is possible to correct this by re-soldering the valve onto its stem to adjust its position.
The original top radiator hose is of an unusual design, with a large convolution. This is because the thermostat outlet and the radiator inlet are very close together, and movement of the engine would place excessive load on the pipes if a conventional hose is fitted. I never did find a supply of these while I was running my car. I have since noticed that hoses known as "hump hoses", for use with turbo-chargers, are similar in shape, although usually with a less pronounced bulge. These might make a good alternative in the absence of the original type.
Engine (Fuel System)
The fuel pipe exits the tank from its underside, which makes it awkward if blockages occur. If the tank has rusted during long idle periods, then the pipe may block if the tank filter is not in good condition. This filter is a soldered brass gauze assembly. Early cars (up to about 1950) also had a low mounted fuel filter on the bulkhead, which is below the tank level. If it has to be disconnected, the front/left of the car should be jacked up first.
The electric fuel pump I found on my AC, was an S.U. type AZX 1332. However, the SU company lists this as a high-pressure pump for mounting at the fuel tank. So, I assume that the low pressure equivalent, will be the AUA25. These are reliable just as long as they are in frequent use and are correctly maintained. If you ever dismantle the pump and refit/replace the diaphram, remember that it needs to be tensioned by applying current to the solenoid while the casing screws are tightened up evenly. Repair kits and new pumps are still available, although some components differ from the originals. These electric pumps are often criticised by owners and mechanics, but it is improper over-haul and maintenance that renders them troublesome. They have given reliable service on ACs, Morris Minors, Land Rovers, etc. for many years, so if persistent problems do occure, then past mis-treatment of the pump will be the root cause. I have heard of diaphrams shrinking, in which case it will need to be dismantled and re-assenbled so that it can be re-tensioned. Lack of use can cause trouble with the contacts (especially in damp climates), and these should be cleaned with something soft - certainly nothing abrasive. This is probably the most common mis-treatment of SU pumps, when contacts are damaged by cleaning with abrasives. Electronic versions are available which removes the contact breaker issue. Fuel supply troubles are often caused by other issues such as blockages. Check to see if any debris is building up in the fuel filter bowl. If so, check the gauze filter in the petrol tank outlet. It might also help to have the inside of the tank resin coated to prevent internal rusting.
The S.U. carburettors are type HV2 Thermo. Parts and repair kits are available from Burlen Fuel Systems. Very little wear takes place in the throttle-spindle holes in the casings, so renewing the brass spindles should take up any wear. I would recommend oiling the throttle spindles occasionally. One potentially dangerous problem with the float chambers, is that if completely drained at any time, the float valve may stick open. I found this to be even more likely with the replacement (modern) valves installed. The solution is to place washers under the float to prevent it from dropping to the bottom. Old washers from the carburettor jets are ideal.
Please note that these old style SU carburettors do not have the oil damper in the top of the dashpot that later SUs had. The more modern SUs found on many classic cars, had a plunger attached to the filler cap, and this required a certain amount of oil to function. The old SUs found on most AC 2 Litres use trapped air to provide damping. This does require a small quantity of oil (SAE 20/light machine oil/bicycle oil) to seal the air in at the bottom. The small hole in the cap restricts the flow of air as the piston rises, giving the required damping. When the engine is switched off, if you lift the piston quickly, any excess oil will squirt out through the hole in the cap.
I'm not sure how often these should be cleaned, but the procedure is to open them up and wash out with petrol or kerosene oil. Then dip them in engine oil (the dirt sticks to this) and reassemble.
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