Waterways and Overheating by Peter Lawson.
This tip was sent to me by our member Richard Perkins and is from an article by John Hopwood of the PWA7 Club. He wrote it after finding a heat distorted head gasket after the ’97 JOGLE. He said that it does improve the cooling significantly. After rebuilding several engines for local A7 owners, he found many of these waterways totally blocked – especially the 5/16in one. Lying between No.2 and No.3 exhaust valves it is vitally important for their cooling.
John’s original article stated: One source of overheating is a restriction of cooling water flow from block to head in the hottest part of an Austin Seven engine, that is between the two central exhaust ports.
There are two waterways in this area and due to the high metal temperature, they scale up much faster than the others.
Next time you have the head off, drill them out in both the block and head as shown.
He continues to say that when drilling the 5/16 hole out in the block it will remove some virgin metal, which, of course, increases the surface area for cooling. It must also be drilled deep enough to break through into the transverse waterway just above the tappet chest. This is way past the manifold stud and is typically 1.25in to 1.5in deep. Richard says that he found blocked waterways on two engines he had rebuilt and had to drill virgin metal, as John says, as though the block had not been cored properly.
Richard said he found a dramatic improvement to what he thought was a different problem i.e. fuel vapourising in the updraught carburettor on long hill climbs. The problem disappeared.
If you do this modification make sure that you don’t block the hole up with the central manifold stud. Keep the stud short enough and use thread sealant to stop water seepages.