The original oil filters for the MGA are canister type assemblies with a replaceable filter element inside. The filter element is held in place firmly against the top abutment by a spring loaded plate at the bottom. Oil enters through the side of the canister in the earliest assembly, or through the side of the head assembly in later units. The oil then passes through the filter element from outside to inside, and then upwards into the engine block. In the filter head assembly there is a pressure relief valve that will allow oil to bypass the filter in the case that the oil flow rate exceeds the flow capacity of the filter element. This should occur only if the filter element is badly clogged, which should not ever happen if the oil and filter are changed at the specified scheduled intervals. All filters designed for this application have sufficient flow capacity to filter all of the oil entering the engine block, assuming the filter element is not clogged.

All of these filter assemblies use a square section rubber o-ring for a seal where the filter assembly mates to the engine block. It is good practice to change the rubber o-ring every time the filter is serviced, as an old seal left in place will eventually age harden and crack, allowing leakage of oil under pressure. A hardened rubber o-ring is difficult to extract from the groove in the engine block, but it should never be left in place with another o-ring installed on top of it. Use a sharp pointed awl or small screwdriver to dig out the old o-ring, and be sure to get it all out and clean the groove completely. Also in all cases when servicing the oil filter, be sure that the parts are reassembled in the correct order with nothing missing. Especially be sure that the spring and plate below the filter element are in place. Also clean and inspect the filter head occasionally to assure that the pressure relief valve will function properly (just in case it ever has to).

The early Tecalemit oil filter assembly is identified by the full height one piece canister with the oil entry fitting on the side of the canister. In this case the filter head is inside of the canister with a rubber o-ring seal around the filter head. Note that this o-ring is not the same as the one between the canister and the engine block. When changing the oil filter the oil supply pipe must be disconnected from the canister. The connection fitting at this point is a banjo bolt which is sealed with two copper washers. These copper washers may be reused a few times, but will eventually work harden and be squashed flat and may eventually leak. It is a good idea to replace these copper seal washers at least once during your ownership of the car, especially if the service history is uncertain. If your car is fitted with the optional oil cooler, the filter assembly will be connected with a large rubber hose in place of the original steel oil supply pipe. This makes it easier to R&R the canister if you leave it connected to the hose, but it may be a little more effort to clean the canister while it's still attached.

The late Tecalemit assembly and the Purolator assembly both have a filter head which is separate from the canister. These filter heads mount to the engine block with an o-ring, and the canister then mounts to the filter head with another o-ring, and the entire assembly is held in place with a single long bolt through the center. For these assemblies the two rubber o-rings are identical. This arrangement makes it easier to change the filter, as you do not have to disconnect the supply pipe from the filter head. Unfortunately, many replacement filter elements are supplied with only one o-ring of the correct size in the package with the new filter. This rather encourages the practice of replacing only the lower o-ring when servicing the filter and leaving the upper o-ring in place. It is imperative that the upper o-ring also be replaced, at least occasionally, to prevent leakage of oil under pressure. It is good practice to do this every time the filter is serviced just to be sure that it doesn't get neglected in the long run. Unfortunately this requires you to disconnect the supply pipe from the filter head, which pretty much negates the advantage of the two piece assembly. However, with due care and judicious record keeping you might arrange a schedule to change the upper o-ring less frequently, but I would recommend that it be changed at least every second year regardless. Also the optional oil cooler installation with the hose connection to the filter head makes it easier to R&R the upper o-ring.

The primary visible difference between the late Tecalemit and the Purolator assemblies is that the late Tecalemit unit has a large steel dome washer welded to the bottom end of the canister, which the Purolator assembly does not have. These units use different center bolts, different springs, different flat washers, and different seals on the bottom end. Because of the difference in canister design the bolts and seals cannot be interchanged. There are minor differences in the construction of the filter heads, but this is insignificant, as they all serve the same function, including a bypass pressure relief valve, and they all use the same replaceable filter element.

OIL FILTERS which can be used with the original canister mount:

AC 32A all paper	Crosland 418 metal ends	Napa 1300 metal shell

MGA Service Parts List original number - 8G683
Filter Dimensions (from the Crosland book):
OD=71.43mm (2.81in)   ID=33.06mm (1.32in)   Height=102.93mm (4.05in)

Moss Motors lists:
    Crosland brand paper filter - 435-355 - Obs No. refers to late TD & TF (same as MGA & early MGB).
    Crosland brand felt filter - 950-010
    Various makers felt filter - 950-510
    Crosland brand paper filter - 950-030
    Various makers paper filter - 950-530

Victoria British lists:
    Unspecified brand felt filter - 3-104
    Unspecified brand paper filter - 3-121

AC - 32A (two sealing rings included)
AutoPartsWarehouse.com - A6000-43179 (Crosland filter)
Baldwin - P172
Beck/Arnley - 041-8069 (this is currently a Crosland 418)
British Leyland - MF21
Crosland - 418 (paper over paper)
ExpressAutoParts.com - A6000-43179 - (Crosland filter)
Fram - CH814PL
Hastings - P172 (obsolete part)
NAPA Gold - Fil1300 (metal over paper construction, three sealing rings included)
M.G. - GFE102 (paper filter)
MAK - MO5109 (1/2 inch taller)
Purolator - L20021
Purolator - MF21 (old part number)
Specialists Choice - MF21
ThePartsBin.com - A6000-43179 - (Crosland filter)
TJ or Tecalemit - FG2471 (felt type, made in Great Britain)
TJ or Tecalemit - FP3317 (paper type, made in Great Britain)
Unipart - GFE102* (paper over paper construction)
Unipart - GFE218* (felt media construction)
Wix - 51300 (metal over paper construction, three sealing rings included)

* Unipart may have various vendors' filters in their box.

Seal Rings are all rectangular section rubber rings. The most commonly used seal ring fits to the engine block for one and two piece canisters, and to the bottom of the adapter on the two piece canister (Illustration #15 above). Most filters will include one ring of this size, and sometimes two. Dimensions of this ring are:
OD=3.16 in   ID=2.90 in   Radial Width=0.130 in   Thickness=0.150 in
You may want to order a spare for this seal, in case you do not get two with the filter.
Moss - 435-335   Sealing Ring
V.B. - 4-730   O-Ring

The second ring usually included with the filter is slightly smaller to fit inside of the one piece canister around the internal filter head (Illustration #16 above). Dimensions of this ring are:
OD=3.00 in   ID=2.86 in   Radial Width=0.070 in   Thickness=0.120 in
Moss - N/A
V.B. - N/A

If you get a third seal ring in the package, with luck it will be the same as the first ring, as you need two of these seals for the two piece canister assembly. If you get a third ring which is different size from the others, that would be for some other application, not used for MGA or MGB (possibly for the late MG TD and MG TF canister).