Plain vs. Roller Bearings
This is a topic that really gets the hare running!
E.S. Cox sets out the problem in his book 'British Railways Standard Steam Locomotives'. He says "Much argument attended the question as to whether the coupled axleboxes should have plain or roller bearings". By the 1950s the evolution of the plain bearing with a pressed in brass bearing, whitemetal lined and generously lubricated had resulted in bearings running over 100,000 miles. Roller bearings promise much higher mileage albeit at much greater expense. The problem was deciding if the greater expense of a roller bearing would be saved by a reduction in maintenance.
Initially it was decided to build the Class 7, 6 and 5 locomotives with roller bearings throughout. In the Class 7 Britannia class, nos 70035-9 were built with plain bearings on the leading and trailing coupled wheels, whereas 70040-9 had plain axleboxes on all coupled wheels and the trailing truck. However, as Cox says, "no superior merit was discernible for one over the other".
So which way for Hengist?
The debate has not changed much since the original design of the Clans - is the additional cost going to provide long term savings versus plain bearings. Some points to ponder.
- A roller bearing has to be fitted to the axle before the wheel is pressed on. If the bearing fails, the wheel has to be pressed off. The Britannia's had problems with wheels slipping on axles which is a very serious problem and can cause expensive damage to the coupling rods. Ideally once the wheel is on the axle it never wants to come off again.
- Roller bearings can be susceptible to brinelling. Brinelling is the permanent indentation of a hard surface. Brinelling can occur if a locomotive is stationary for a long time when the weight of the engine is resting on the small surface area of the rollers. For this reason, it is normal to move locomotives fitted with roller bearings every few weeks or so. However the tender and front bogie will definitely have roller bearings, therefore the engine will need to be moved anyway.
- Roller bearings offer less frictional resistance, especially when setting off.
- Repair of roller bearings will be more expensive.
- Despite problems with the roller bearings on Tornado (believed to be a one off problem), the A1 Trust have ordered roller bearings for the P2 project.
This one is subject to much debate within the group and we shall be consulting with other groups before making a final decision.