Successful repair of Field Marshall tractor 3A decompressor mechanism
This Field Marshall tractor – a late series 3A model is actually one of our own. It was purchased earlier this year to go alongside our series 2. It had been in a collection for many years and required various small bits of maintenance to allow it to be used. One of these items was the decompressor mechanism. This is a spring loaded plunger with a small wheel on which engages with a spiral groove on the flywheel. It is set on the flywheel to pull open a decompression valve and then as the flywheel is turned with the handle, it travels along the groove until it finally drops off, allowing the decompression valve to close and the tractor to start.
The issue with this particular one was wear in both the plunger in its housing, and the guide wheel and shaft. This meant that the guide wheel was not running at 90 degrees with respect to the grooves on the flywheel meaning the tension from the spring loader plunger was causing it to jump across the grooves rather than follow them. It meant when start the field marshall tractor, you would not know when the decompression valve would close making it impossible to start by hand.
After reaming out the housing and guide wheel, new parts were made with the correct clearances and then assembled. The result is a smooth and accurate mechanism once again. A test of the repaired mechanism has proven this to be successful and resolved the issue. This was a case of identifying the problem, working out a solution and then implementing it.
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Field Marshall Tractor
The Field Marshall tractor was a popular British tractor manufactured between 1945 and 1957 by Marshall, Sons & Co. of Gainsborough, Lincolnshire.
The development of the Field Marshall tractor began during the war, when the British government began to investigate ways to increase food production in the country. Marshall, Sons & Co. had a long history of manufacturing steam engines, threshing machines, and other agricultural equipment, and they were asked to develop a new tractor for British farmers.
The first prototype of the Field Marshall tractor was built in 1945, and it was immediately clear that the design was a success. The tractor was equipped with a powerful single cylinder 2 stroke diesel engine, which gave it the ability to perform heavy-duty tasks. It was also designed to be easy to maintain and repair, which was important for farmers who often had to do their own repairs in the field. Being powered by diesel meant it was very cheap to run.
The Field Marshall tractor quickly became popular with British farmers, and it was exported to other countries around the world. It was particularly popular in Australia and New Zealand, where it was used for a wide variety of agricultural tasks.
Over the years, the design of the Field Marshall tractor was refined and improved, and several different models were produced. In 1957, however, Marshall, Sons & Co. stopped manufacturing tractors altogether and turned their attention to other products.
Today, the Field Marshall tractor is remembered as an important part of British agricultural history. Many tractors have been preserved and restored by collectors and enthusiasts, and they continue to be admired for their rugged reliability and simple, elegant design.
