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Last updated:
31 January, 2023
Side, or top, water manifold modification.
Don’t do this if it isn’t leaking. If it ain’t broke don’t fix it!
There are many features of the Austin Seven that can be a cause of irritation, usually the result of poor design.
Over its lifetime the car underwent many alterations, both major and minor, but surprisingly a couple of components that went unchanged, are the aluminium castings that are the water manifolds on the engine. It is true that the material used in the sand casting was varied, (aluminium where weight was an issue; bronze for a marine application and cast iron for general industrial applications), but all of these parts share a common fault – they are prone to leakage around their fixings. It doesn’t help that the combination of aluminium for the manifold body and steel is a recipe for corrosion and both side water and top manifold castings suffer badly over time in this respect. The gasket face provides a useful barrier against corrosion and thus leakage, but it is where the stud emerges into the outside world that leakage occurs around the thread of the nut and its washer. A fibre washer is the usual solution, but some coolant inevitably seeps up the gap between the stud/body gap and the screw thread.
A better solution is to use an ‘o’ ring on the stud fixing because the rubber ring squashes into the gaps to provide a seal. Putting a blob of sealant on the stud before screwing up the nut and washer will provide a rather messy solution. What is needed is a seal around the non-threaded stud area which is the point of this modification. (‘O’ rings are made with a specific I/D and ring thickness which determines the subsequent O/D. They are usually made from nitrile or silicone rubber which withstands the operating coolant temperatures).
The procedure involves drilling a 45° countersunk hole on the end of the stud hole(s) as shown in the image, the diameter of which is approximately the same as the O/D as the ‘O’ ring you have chosen to fit closely around the stud (I/D=5/16”). The idea is to compress the ‘O’ ring into the space of the countersink so that it fully grips the stud surface and the surrounding countersunk cavity. Place a fibre washer of the appropriate diameter above , followed by a steel washer and tighten the nut on top.
The result is a sound seal which can be cleanly dismantled, and the resulting assembly invisible to ‘rivet’ counters!. This method ensures that the seal isn’t merely squashed against the threaded part of the stud. If ‘O ’rings had only been in use when Sevens came out we would have been spared a great deal of hassle!
This article, written by Bob Kneale, originally appeared in CA7C Seven Focus in February 2023 pp13-15.