Modifications to Duke’s front end
UNIQUE BR 8P 4-6-2 No. 71000 Duke of Gloucester is receiving modifications to its front end to improve its reliability and ease maintenance.
As part of the Riddles Pacific's overhaul to main line standard at Tyseley Locomotive Works, the design of its pistons, slidebar mountings and lubrication system have all been altered to tackle design flaws – which meant that the Duke and other Standards suffered from heavy piston ring wear.
In common with all of the larger BR Standard classes, except for the Caprotti-geared 5MT 4-6-0s, No. 71000's slidebars were affixed only to brackets from the frames instead of being attached to the rear cylinder covers – meaning that any flexing between the cylinders and slidebars would increase the piston ring wear.
The Duke's slidebars will now also be attached to a bracket incorporated in the rear cylinder cover casting, which will provide better support for the crosshead and pistons.
The main cause of the heavy wear, however, was the lubrication system; Cowlairs Works found that the Caprotti-geared 5MTs, with their slidebars fixed to the cylinders, suffered only 10% to 15% less piston ring wear than their classmates with Walschaerts valve gear.
The main weakness in the BR Standard lubrication system was that it fed oil only to one end of the cylinder; on the Duke, it will be modified to reflect the LMS design, which delivered oil to both ends.
In addition, No. 71000's piston heads will now be separate cast iron fittings, instead of the piston head and rod being a one-piece steel forging as on the original design. This will make replacement of the heads easier, by removing the front cylinder covers and drawing the pistons through the cylinder.
“As the originals wore, you had to build them up with weld,” explained Trevor Tuckley, chairman of the locomotive's custodians, the BR Class 8 Steam Locomotive Trust. “But in that environment, that's the worst thing you can do, because weld is very hard and if it starts to break up, it scores the cylinder.”
They will also have three piston rings instead of the original two – this time copying the rebuilt Bulleid Pacifics. “They didn't suffer from anything like the same degree of wear that the Duke did,” explained Trevor, “and we think that was for two reasons – firstly, they've got a shorter piston stroke, but also because they've got three rings.”
Trevor concluded: “These are all the modifications that we believe Riddles would have done if he hadn't been told ‘forget steam, we're going for diesel'.”
Trust volunteers have also fitted a kitchen to their newly-acquired support coach, BR Mk.1 Brake First Corridor No. W17015, and cleaned the paint from its roof in preparation for its imminent move to Rampart Engineering at Barrow Hill for overhaul.
The trust's appeal to overhaul the coach is just over 60% of the way to its £40,000 target, while 80% of the Duke's superheater flue tubes and 56% of its small tubes have been sponsored. To support any of these appeals, visit www.theduke.uk.com or write to: The Duke, BR Class 8 Steam Locomotive Trust, Aurora House, Deltic Avenue, Rooksley, Milton Keynes MK13 8LW.