by Norman Nock
Originally published in the Austin-Healey Magazine, June-July 1987
This sounds like an easy job. The oil filter is in a metal housing bolted to the side of the engine block on all Big Healeys. Just pull it off and replace it, right? Wrong! There are many potential problems associated with this seemingly simple task, and herewith are some examples.
For most people, the first step in replacing the oil filter is to remove the long bolt (#14 in the illustration) from the end of the filter housing. Then the dirty filter is removed from the housing and tossed into the garbage. What has now happened is that the metal end plate, which fits in the housing under the oil filter, has stuck to the filter and gone into the garbage with it. Without this plate (#9 in the illustration) pressing on the spring (#12), the new filter will not be in the correct position within the housing, and the oil flow will not be through the filter, but will be bypassing it completely. And for the filter to do its job, the oil must be forced to travel through it, not around it.
Another common problem involves the rubber "0" rings (#3) which come with filters. This ring must be fitted into the slot in the oil filter manifold (#1). However, quite often our service department finds two of these rings jammed into the slot. When this happens the oil flow is restricted to the point of stopping the flow to the filter, and if this happens the oil will bypass the filter.
Another fairly common problem involves the early series BN4 cars. This model came with a filter covered with a wire mesh ("Vokes" brand filters). This type of filter is not available any longer, and for the paper or felt type filters to work properly it is necessary to fit the dished washer (#7), the felt washer (#6), and the filter plate (#4). If these parts are missing and there is no provision made for them, you should replace the oil filter manifold with a later type which has provision for these essential parts.
You must also be careful to replace these parts (#4, #6, and #7) in the proper sequence. If the plate (#4) is put on first it will restrict the oil flow. The correct procedure is to replace your oil filter as follows:
Do not remove the long center bolt (#14) first. Instead, remove the two bolts (#40) which hold the oil filter manifold to the block.
Now, with the whole unit removed from the car, remove the long center bolt and check to insure that all internal parts are present and in their correct position as you disassemble it.
Wash and clean all parts, and insure that the seal (#3) is removed. Check very carefully to insure that there is not an old, hardened seal jammed in the groove.
Fit a new seal, insuring that it is a snug fit. If the new seal is a sloppy fit, do not use it - it is the wrong size and will not do the job!
Reassemble as per the diagram. With all parts in their proper places you'll notice that the filter spring pushes against the bottom of the filter housing and that it is necessary to compress it somewhat to tighten down the long center bolt (#14).
Replace the manifold gasket (#35), and refit the assembly to the engine block by replacing the bolts (#40). Do not use any type of sealant here which could squish into the oil passages and restrict oil flow.
Finally, a word about oil pressure. If you think your oil pressure is low (say, 20 Ibs or less at idle), the accuracy of the gauge should be your first suspect. Have a good quality professional gauge connected to compare with your gauge.
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