 Lots of people have adjusted the valves on their beloved pre-wars on periodic maintenance. Which is a good practice to do regularly. It’s a precise job that, with very simple tools (wrenches, feeler gauges) can be done in the home shop as a part of regular maintenance. In this article, I want to address a different system of adjusting the clearance than with the usual system of a threaded end of a rocker or cam followers. The system I am describing today is of a Bugatti Type 57 engine. But in this or different forms it is found on many other pre-war cars especially on veteran and brass-era engines. The cam, valves etc are non-adjustable and use either shims, cups or some type of bushing to adjust the play. This means that parts have to be made or altered to adjust them. Accurate measurements are needed in this process to get it spot-on. First, check the clearance when the whole assembly is still assembled. Do this with a dial-indicator if available. This is because when the camshaft and followers have a little wear on them, it is possible that a feeler gauge rests on the unworn area and does not measure accurately. (see sketch 1). Then take the assembly apart, carefully marking the correct cap/shim or bushing with the correct valve. Then measure the thickness of each cap separately and write down what the correct thickness should be to get the correct clearance. Then new caps should be made from hardened steel, ground to the correct dimensions. Please make sure you get the correct material. If it’s too soft, they will wear excessively. The PreWar Workshop can advise in this or get you the correct parts. After this, everything can be mounted back in place and make sure to re-measure after it’s correctly fitted to make sure the clearances are OK! For a graphic explanation, please view the photo album here: https://goo.gl/photos/zJWBre6ngJp3V7LA6 Article written by Jos van Genugten |
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PWC Workshop: Valve clearance issues
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