[alfa] Of exploding oil filters !

["John Fielding" <johnf@xxxxxxxxxxxxxxx>]

Hi All,

Isn't amazing how the same thread keeps raising its head every couple of years?

The exploding oil filter syndrome is a design fault in the Alfa oil pump pressure relief
valve.  This has been known by the factory for eons but nothing was ever done to cure the
problem.

The plunger is a very close fit in the bore and just one tiny bit of grit will jam the
plunger, preventing it from moving.  It can jam in the closed position, in which case the
excess oil pressure has no escape route and the pump can deliver well over 20bar (300psi)
when the oil is cold, hence exploding filters.  It can also jam in the fully open position
which then gives an abnormally low oil pressure at idle when the engine is hot.  I have
had brand new pumps with jammed plungers after just a few hours of running, it really
is a cr*p design!

If you take the oil pump out and then strip the oil pressure relief plunger very often the
plunger will not move even with compressed air.  The best cure is one Jim Steck suggested
a few years back.  This uses a large ball bearing to replace the plunger and entails a
little minor surgery to the bore to grind in a little nick for the oil to flow past the
ball to the escape hole when it lifts.

If/When you do eventually manage to strip the pump plunger out of the bore, this can be a
real character building exercise, look carefully at the side of the plunger face where it
normally covers the oil escape hole in the bore.  You will see that it is scoured by the
dirt in the oil giving a narrow strip about 4mm wide and extending about halfway up the
plunger from the closed end.  The pressure relief valve is after the pump and before the
filter, hence any tiny bits of muck in the oil will cause the plunger to jam.

Since doing this modification to my race Alfetta I have had no further problems.  BTW  The
CV ball bearings used in the Alfetta rear drive shafts are exactly the correct diametre
for this modification, cost is zero if you have an old CV joint in the parts bin.

John
Durban
South Africa
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