Water Pumps

[Running Board]

Does anyone know anything about running clearances for the water-lubricated bushes used on Asturas, Augustas and Aprilias (and also, I dare say, probably most Sola designs of the 30s)? 

When I rebuilt the Astura engine in the early 80s, I noticed that the water pump bush was worn (visibly oval).  I reamed it out from 12mm to 13mm and made a new spindle from 1/2" (12.7mm) stainless round - which worked well for many years and about 15 000 miles.  Then it seized solid, shearing the drive!  I fitted a spare pump which has very generous clearances and that has been on about 5 years and seems OK, but there again, so did the last one!  With Augustas, there's plenty of room to fit a modern seal and bearing and get around the problem, but there is not much room with the Astura pump (the timing chain tensioner pivots on its nose: yes, it's buried in the depths of the engine and best left alone!). 

Tilling-Stevens used the same idea on their huge (5 litre plus) 4 cylinder petrol engines of the 20s/30s, but the only information I can glean is that they used a nitrided steel spindle running in a bronze bush.  Lancia spindles for the models mentioned seem to be stainless and run in a bronze bush too.  But what sort of clearance, I wonder?  The same technology on a much larger scale is of course used for stern tubes of power boats and ships.  I have, incidentally, already tried PEEK for the bush.  This is a space-age self-lubricating bearing plastic having a melting point in excess of 250 degrees C.  Ideal you may think.  But, the friction of the pump packing gland raises the temperature of the spindle (locally) to more than that figure!  Oh what a gooey mess!!! 

So, are there any marine engineers out there with knowledge of these things?