DEISEL REPORT

It feels like I'm writing these reports every week..... not so of course but where is all the time going? We have had a busy time of it lately with our lovely oily machines, they have been working well with a few minor faults here and there but in general all available at some point.

The Class 37 has had an annoying fault since its arrival where the main air reservoir gauge at No. 2 end was always under-reading. This was eventually traced to a corroded pipe leaking air under the cab floor. Not the easiest of places to access. The driver’s seat had to be removed and the floor lifted, but a repair was eventually made with some minor modifications. Not long after another air leak was reported and found to be in the same location but in a different pipe, this time in the driver’s locomotive straight air brake system. The corroded section has been removed with new pipe and fittings now installed. It takes but a few seconds to write that about, the repair took several days. When these locomotives were built, a lot of the pipework passing through bulkheads was welded in place, possibly a good idea at the time considering the intended lifespan of the locomotives, but very prone to corrosion in later life and difficult to repair.

The Class 27 has been out earning a crust on the June Diesel Fridays and now with a working roof fan at last, all credit to Andrew Caldwell for his detective work and persistence in getting that problem sorted. The roof fan maintains the engine lubricating oil at a constant pressure by keeping the engine coolant at an optimum working temperature. The fan cuts in and out, controlled by thermostatic switches located in the water header tank. The fan vents excess heat by drawing air through the radiators and out through the roof opening. When the fan is not working the coolant gets very warm, so the oil also gets hot and the viscosity reduces, meaning the oil does not lubricate efficiently as it is much thinner. Added to this the oil pressure drops, if the pressure drops below 18psi the engine will shut down to protect the moving parts from damage. Now that the fan is working properly the oil remains at a more constant viscosity and pressure. Much better for engine life and reduces the risk of excessive, potentially damaging wear.

All three main line diesels were used on the June diesel days, and all performed excellently, apart from a leaking vacuum bag on the Class 31, a wonky windscreen wiper and a lighting circuit breaker tripping. A good result and testament to the dedication of the group of volunteers who help look after these machines.

One exciting event, in the wrong sort of way, was a small fire in the exhaust of the Vanguard shunter. Caused by a long-time build-up of carried-over oil and other nasties settling in the exhaust, as it heated up this residue ignited with lots of smoke issuing from everywhere. It was quickly extinguished with no damage done. Options are being considered to replace or modify the exhaust system as it was already in a very poor state before the excitement, and we would rather it did not happen again.

Rob Atkinson has been working away with the Barclay shunter engine repairs, he has had a frustrating time lately, a case of one step forward and several back. The engine has been reassembled and started, however Rob noticed bubbles rising in the radiator. This can only be combustion exhaust gases leaking from somewhere into the coolant system. This engine, a Cummins straight six, has the cylinder heads arranged in pairs, one of which was possibly faulty and allowing the exhaust gases to leak. After some more investigation, meaning the cylinder heads were removed and examined, a small crack almost invisible to the naked eye was found by using an NDT (non-destructive testing) dye penetrant method. A red coloured oil-based dye is applied to the suspect component surface, after a short while the excess dye is removed then a developer (basically chalk dust) is sprayed on, this draws any residual dye out of any cracks revealing the whereabouts and extent. Two options are possible to fix this, firstly weld the crack up. The weld is possible but very difficult, in the area of the crack the casting is very thin, and the repair could fail or maybe not last long. The second option is the better way to go, replace the head. Rob has located a company that supplies these and is at present chasing this up. As ever Rob's persistence is admirable, he does an amazing job, not just at the railway but also researching and sourcing parts when at home..

- Dave Green,