6940 Haulage for June 14th

We are delighted to announce that 6940 is confirmed as fit for traffic following a successful solo test run last night. We now plan to use 6940 on the next scheduled running day on Sunday the 14th June.

This is a brilliant result of which we are all very proud given the numerous challenges the loco has thrown at us over the last 2 years. A massive thank you to all who have lent their support – physical, technical, financial and moral!

Thanks to Pete Coole for grabbing the below photo at Goods Junction before heading off down the line with Mark Smales to check all was well. A quick tweak to black and white and suddenly it’s all gone very 1970’s!

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The Story of 6940’s Return

Work has continued apace on the loco since her successful 28th March test run, with our Chairman Mark Smales putting in a lot of hours. The earth fault preventing use of all 6 traction motors was traced to water ingress into a cable junction box under the radiator room. Many thanks to Paul Warren at the Wensleydale Railway for his help with sorting this after he had an identical problem with 37250 after a lengthy period out of use. The errant box is seen below after the cover had been removed. Holes have now been drilled in the cover to allow drainage so we hopefully won’t have to squeeze into this cramped and filthy area again. If you ever wondered what 51 years of accumulated grime looks like then wonder no more, Mark has kindly provided a photo for you!

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The air system was the next task. A passing combined brake valve was replaced in number 1 end with a spare from our stores. The spare was not in the best of health either, so was subject to a full strip and overhaul before fitting to the loco. It appears to be fine, which is a relief seeing as we had rebuilt the desk around it before testing it in anger! The loco had also been struggling to make and hold adequate air pressure for some time before her forced withdrawal in 2014 and was declared a failure in summer 2013 when the large compressor overheated and cut out.

For some time we suspected the large Westinghouse compressor had a fault as it was passing air through the oil dipstick and only making around 110psi. Like most BR locos, 37’s have two compressors – a lower duty original fitted when the loco was built, and a second, larger one fitted by BR for use with air-braked trains later in their working lives. Both live in the cramped environment of the Number 1 nose end, stacked on top of one another and very difficult to get to for anything other than oil top up. The photo below shows the smaller compressor – which sits under the larger one. It’s not actually possible to get a photo of both unless you stand on your head or lie on the nose end floor. Neither are recommended!

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The large compressor was lifted out using the crane on Mark’s recently overhauled Unimog for inspection on 10th April. The cylinder heads were carefully removed and the valves inspected, which were the first- suspected culprit. Apart from some accumulated dirt they were fine. Back to the drawing board then!

The next gambit were faulty piston rings in the high pressure cylinder, something we hoped wouldn’t be a problem as they are now very hard things to come by. A strip down confirmed this to be the case, with the bottom of the 3 sealing rings damaged on the high pressure piston, as Mark’s photo below shows. The challenge was now to source replacement rings – and a challenge it certainly was!


A number of potential suppliers were approached who were helpful but could not supply us with off the shelf parts. Having new rings made would need a lot of money, take a lot of time and need full a drawing, none of which we had to hand! We were extremely grateful to the Northampton Type 2 Group, who kindly offered us the loan of a spare Westinghouse 3CV50 compressor – it turns out the same type was used on the Class 27 as well as 37. However, identifying whether the faulty compressor was indeed a 3CV50 proved a challenge. The loco’s original BR documentation only specified the 3CV50 compressor, which is the low duty original and a 3 cylinder unit. The faulty one had two cylinders and no obvious model number on it! After scraping the paint off the maker’s plate, it was finally found to be a Westinghouse 2EC38B. We were learning a lot but not fixing the problem!

The breakthrough came when Mark tracked down some suitable rings from, wait for it, Estonia! God bless the Internet. They were sold as suitable for Westinghouse lorry compressors but the dimensions looked spot on for our 2EC38B large loco compressor. And spot on they proved to be! After fitting the rings, reassembling the high pressure stage and refitting the compressor to the loco it made the correct air pressure straight away! The nose end was given a good clean, as were both cabs. It was then everything crossed for a test run on May 5th, which was passed with flying colours. Big grins all round! (photo by Pete Coole)

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All that’s needed now is a fettle of the bodywork if we can find a dry day to apply polish!

A brilliant result of which we are all very proud given the numerous challenges the loco has thrown at us over the last 2 years. A massive thank you to all who have lent their support – physical, technical, financial and moral!

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