I'll tell you how you can have a clogged screen on a rebuilt
engine. Several months ago I ordered a rebuilt engine for my
'84 Westfalia from a reputable engine builder.

After the first several minutes of running it lost oil pressure.
I went through every diagnosis possible, but it wasn't until
I decided to drain the oil that I found the problem.  There
was a shop rag left in the crankcase!  And I'll tell you,
after being hammered around a while, the rag became finely
shredded and thus clogged the oil pickup screen.

The engine builder, did try his best to rectify the problem,
but I never got a satisfactory motor, and ended up
rebuilding it myself.
>
>
> How can you have a clogged screen on a rebuilt engine?  Maybe too
much
> silicone was used? Is it possible that the wrong oil pump
> cover gasket was
> used?  This would seriously reduce the pumps output.  It
> should be the one
> that is so thin you can almost see through it.  The other
> possibility is
> that a wrong sized bearing was used or maybe a cam bearing is
> missing.  A
> bad lifter will not cause a pressure problem unless it is
> noisy.  The oil
> that flows through the lifters goes through the pushrods to
> lubricate the
> rockers.  You should also check the oil pressure relief valve.
>
> Dennis.
>
>