Good news for suspect Napier Power Unit

When D9015 was started up for the first time in 27 years, shortly afterwards, ominous sounds were heard from Napier power unit 417. This had not run since 2005. It had all the symptoms of being dephased – this is where the three crankshafts do not align correctly and which can be caused by a defective (broken) gear wheel at the end of the power unit which marries all three crankshafts to form a central rotating shaft which turns the main generator.

It was a common fault experienced in BR days and involves lifting out the power unit, removing the main generator, then the phasing case cover (both necessitating a crane) to expose the huge gear wheels. Sometimes it is necessary to remover the complete phasing case to access the ‘triangle’ in order to access a possible broken quill shaft. This is, in effect, a safety device like an electrical fuse which fails first to protect other equipment.

The DPS welcomed representatives from Power Engineering Projects Ltd of Wigan who may well be the only contractor left in the UK capable of overhauling Napier power units. This inspection required the removal of the fuel injectors, so a sophisticated camera could look inside the liners and look at the condition of the pistons.  The engine appears to be in good order in respect of the liners and pistons.  A couple of minor faults were picked up on the liners which was put down to age and hours run. 

The power unit was then barred over and the pistons all moved.  All of the fuel cams were checked and the cams are all in time.  This means that the unit is not dephased as first thought, so attention is now to replace all 18 fuel pumps. Once this is done, Power Unit Engineer, Pete Stojanovic and his team will start unit 417 to see if this has cured the rough running of the unit.

DPS volunteers are working on re-instating to working order power unit 430 which last ran in 55008 The Green Howards in 1981. This Napier was earmarked to be fitted into D9015, but as power unit 417 appears not to be dephased, 430 is now destined for 55009 Alycidon. This is the aptly named ‘triangle’. All internal hoses are being replaced. This power unit had multiple leaks from the injector and blanking plug pockets when it was filled with coolant.  It was decided to start again with a strip down of the pockets and start again with new O rings.  The unit now appears to be leak free. The complete phasing case containing all the huge gear wheels is away for overhaul with a South Wales gear contractor, Compact Orbital Gears Ltd, Rhayader, and found to be in surprising good order considering it has been out of use for over 40 years. This is expected back at Barrow Hill imminently for immediate fitting, followed by the overhauled generator which will then permit the complete assembly, weighing some 11 tons 6cwt, to be lifted into Alycidon.

Here is the overhauled main generator, destined to be fitted to power unit 430, after return from the contractor, Dorlec, based at Clay Cross, Chesterfield. A complete strip down, renewal of parts as necessary and testing costs in the order of £14,000.