Spin-on oil filter

[Nick Jones]

Both the PI and Vitesse have the Mocal spin-on oil filter conversion.  The filter points down on the PI and forward on the Vitesse.

The Vitesse gets oil pressure very quickly in spite of the somewhat tired nature of the engine.
The PI on the other hand has been taking ages to get oil pressure, even after quite short periods standing (couple of hours).  This in spite of the filter pointing downwards, new bearing shells and a carefully fettled oil pump.

Yesterday I popped in to see Chris Witor to collect some parts and mentioned this to him.  His suggestion was that I should check the inner O-ring on the conversion.

There are actually two variants of this conversion.  The early ones have a simple O-ring to seal between the incoming/outgoing chambers and were originally supplied with two O-ring sizes to cater for varying machining tolerances on the block.  There is a procedure to determine which O-ring is needed which was a bit too technical for some ( with occasionally dire results) and later product has a more elaborate spring loaded block and seal which sorts itself out.  Both my cars have the earlier one.

The problem with the earlier one is that if you fit the larger inner O-ring and it is too large, it holds the housing off the outer seal and you get a major oil leak.  This is obvious enough, but graunching the bolt up tighter in an attempt to get it to seal can result in a chunk of the block breaking loose - which is a BAD THING!

On the other hand, if the smaller O-ring is too small, you get no external leak, but you do get an inner leak which you can't see.  This allows some of the oil to bypass the filter and also provides a leak path back to the sump when the engine is off.

Mine proved to have the smaller O-ring fitted and although it was old and hard, it was still round in section with no sign whatever of having been compressed.  I fitted a new outer seal (after 15 minutes cussing getting the old one out) and fitting the housing up with some blobs of blutak to measure the gap.  Sure enough, the small O-ring was WAY too small, so a I re-assembled with the big one.  No external leaks, and early indications are that the oil light goes out after 2 - 3 seconds instead of 6 - 8.  Result!  Thanks to Mr Witor for putting me on the right track  :)

Nick

[DJB_Harvey]

Yes as said above .. Overtightening the central bolt can have dire consequences ..  Especially on earlier 6 cylinder blocks where there was even less metal on the central boss . Eg pre 72/73 ish without the external strengthening rib on the offside of the block .