Morris Minor Owners Club

If the filter head fitted to your 'A' Series has a oil filter by-pass valve fitted - full oil filtration is not possible.
The valve only requires as little as 1.25lbf to lift it off its seat so allowing oil to easily by-pass the oil filter and pass to the bearings.
If you have got good oil pressure the by-pass valve will be open most of the time so allowing crud to flow past the oil filter.
The solution is to remove the by-pass facility.
The valve assy can be easily pressed out of the filter head even though it is retained by either 2 or 3 swages.
Drill and tap the valve hole and fit a 3/8" BSP taper plug and the jobs done. Full flow oil filtration.
The example below is of the screw on filter type but the same process can be carried out with the element type filter head after removing the top filter plate which is lightly swaged to the filter bowl bolt housing.
If using a screw on filter check that the top face of the filter clears the blanking plug which may require a skim of the outer socket face.
WIX screw on oil filter WL7077 fits perfectly.
Be aware that this modification can only be done to the older type screw on filter head or old type element filter head.
Below is the unmodified filter head with the by-pass valve in place :- Here is the modified filter head with the valve replaced by a 3/8" BSP taper plug - use Loctite loc and seal to secure the plug in place:-

Have you noticed any drop in oil pressure, Phil? I guess that it would only be of interest if measured AFTER the filter. I was wondering if the small 'can' has enough surface area to allow the oil to pass without restricting it. Would a larger filter help? The Disco, IIRC, has a mauch larger filter can body but the same filter thread and seal sizes. Not sure if it fits the engine bay, though.

Rob
The filter head has not been fitted yet (it is going on my slow build 998cc Minor engine and a second modified filter head on my 1400cc Midget engine) so I cannot currently tell you if there will be a drop in oil pressure but I doubt that there will be a drop in oil pressure after the oil filter.
The modification is well known but have seen no reference to it on here so here it is.
The WIX filter is quite large 120mm Length x 80mm Dia and should pose no restriction to flow or pressure.
The same filter is fitted to the remote filter housing without by-pass on my Minor and there has been no reduction in oil pressure to the engine. In fact I have too much oil pressure at times on the 1380cc and it does need to be reduced - to that end I have an adjustable oil pressure relief valve to bring the pressure down.
Volume is what is wanted not necessarily pressure.
Phil

I do not understand why BLMC went to the trouble of making the by-pass valve when to all accounts you are better off without it?

The valve is there so that some oil can get past the oil filter if the oil filter is blocked through lack of maintenance.
Not all 'A' Series owners are good at maintenance.

If you want total filtration of the engine oil it is best not to have the by-pass valve especially on expensively built engines. Just change the oil filter on a more regular basis.

If the blocked filter warning light is illuminated (fitted to some Minors) it does mean that mainly unfiltered oil is circulating through the engine which is no good at all.

As Morris Minor owners are very good at remembering to change the oil filter on a regular basis the by-pass valve and blocked filter indicator switch could have been omitted from Morris Minor 'A' Series engines.

Capito !