S.A.C. Martin wrote:And yet it must be telling that Peter Grafton - the only writer out of the hundreds out there - goes into more detail on the work done to 8579 than the rest (which normally equates it simply as a Gresley build and fails to mention Edward Thompson entirely, without saying to what extent modifications were made and how).
Grafton's book seems to be fairer and more balanced than any other book I have read on Edward Thompson, giving both sides of the equation. He mentions with reference to the B12 that Thompson "paid particular attention to the valve modifications. A full sized mock up of the valve gear was made and housed in Stratford works and Mr English relates how he spent many afternoons working out the valve events from the mockup up with Thompson enthusiastically turning the handle which operated it". (Page 26 of my edition. There's a lovely photograph of the preserved 8572, albeit in original condition, and 8579 next to her).
Getting OT for this thread but worth understanding that Grafton bases his discourse on Thompson's walks to Paddington station and listening to the sound that GWR locomotives emitted, attributed to sharp valve events with long travel, high boiler pressure, and a small smokebox.
1. Stratford and A.E. English already had experience with the valve events and long travel valves. Following the Locomotive Exchanges Gresley had already learnt this lesson and was applying it - including to the batch of N7/2s built during 1926/7, most of which ended up at Stratford and before Thompson took up his duties there;
2. B12 8525 was experimentally fitted with Lenz valve-gear in 1928 and then the batch of 10 further B12s ordered from Beyer Peacock in 1928 were specified to have Lenz valve-gear. This proved unsuccessful in that cam shafts were prone to fail due to twisting and monobloc cylinder castings cracked;
3. B12 8559 was the first to be fitted with long-travel valves in December 1930, the design work being carried out at Stratford, so the first stage of the 'secret' modification was not made to the same locomotive as Grafton states;
4. Improvements to the GE permanent way finally allowed an increase the permitted weights of engines, which factor provided for the more extensive rebuilding to what became B12/3, and 8579 was the first in May 1932 - one of the 1928 Beyer Peacock engines that needed attention due to the faults arising from the Lentz valve gear - the penultimate B12 constructed and barely 3.5 years old.
5. It is worth noting that neither the boiler pressure nor cylinder size were changed, so the tractive effort remained unchanged and thus one of the factors attributed to the GWR locomotives (high boiler pressure) was not introduced during the rebuild.
Note that Grafton writes 'It is likely that he [Thompson] proceeded under his own initiative..." but the evidence elsewhere does not support his version of events.
References - the relevant RCTS Parts, and FAS Brown's and Dr. Geoffrey Hughes biographies of Gresley.
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