Presumably you will check out the oil pump while you’re at it? Have you
been getting any of the other symptoms of bad main bearings, like rumble or
vibration? I guess these would be much less pronounced on a 12…I’ve
deleted our previous posts on this subject, but just wonder whether the
problem may be more connected with oil supply than bearing clearances. If
you haven’t exonerated the oil pump 100%, maybe the question of engine
removal turns on the accessibility of the oil pump. A quick look at my
series 1 V12 manual suggests it may not be as straightforward as the good
There do not seem to be many reports, if any, of oil pump failure on V12s.
However, Bryan’s is a rebuilt engine and it could happen.
The oil pump has a rear half of cast iron, but the front half is alloy and
shows some minor scoring on the HE engine I am rebuilding, although it is
not going to be a problem.
Possibly there is a problem with the pump or something else and nothing much
wrong with bearings.
Maybe the oil pipe from the pump to filter block has a poorly fitted O ring
and this is causing pressure loss.
It sure is no quick job to get at the oil pump, but listers have pulled the
timing cover off without taking the heads and sump cover off and then you
can get at the pump.
I guess if you could rig up a gauge to test the oil pump itself it would be
handy, but that is not easy. You need to take off the oil filter block and
put in something to measure oil pressure. In Bryan’s engine the pressure is
falling off when the engine is hot, so you have to test a hot engine. The
oil gallery to the bearings has to be shut off for a few seconds with a
running engine to see if the problem is pump or bearings.
With an engine doing 2000RPM on no load the bearings would not suffer if
pressure was lost for a few seconds.
I have a filter block in pieces, and my guess is an adaptor could be made to
bolt on the engine block and fitted with gauge plus changeover valve to
carry out this procedure. It can be a bit rough and ready, since the whole
thing only needs 15 minutes of use to let the engine warm up, and then a few
seconds for the test. If my life depended on it I think 4 hours work would
do it using an old filter block and a cheap industrial valve. There is
already a tapped hole with blanking plug on the rear of the filter block.
Of course, this does not cure the problem. It might tell you the pump is
shot or the bearings are shot or both are shot. One way or another you have
some serious work to do. It would be a pity to replace bearings, if ruined,
then ruin another set because the symptoms were cured but the cause overlooked.
Richard Dowling, Melbourne, Australia, 1979 XJ-S & 1985 XJ6.
Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !