Model Engineering Articles

Loco Maintenance

It is some time now that the workshop has been left to its own devices. An occasional visit just to check that the dreaded rust has not taken hold, but for a variety of reasons I have not felt either the enthusiasm or drive to get stuck in. I have a few jobs still needing finishing but for now I have decided it is better to wait it out. From bitter experience I know that when you are not totally convinced that it is time to start some new engineering endeavour any attempt is half-hearted and usually, in my case, the resultant work ends up in the bin! Years ago I would eagerly send off for drawings and castings for a new project and it would take wild horses to keep me from starting and sometimes in my hurry to get the project finished, mistakes would be made. For me this is just a hobby and if it isn't enjoyable then it's time to give it a rest and find some other pastime to keep me busy in the interim.

Having said that, I have had a rather a long workshop rest-break, that is until recently, when a set of 'castings' arrived. The 'castings' in this case were the return of my 7-1/4" Wren loco. The engine had done yet another summers hard work pulling passengers around the club half-mile track. The engine was completed in 1997 and each year since then has been gainfully employed, and so on its return this time it was perhaps in need of a thorough check-up and a bit of maintenance. For the last two years I have entrusted the job of running and care of the engine to my friend Jack who is very diligent and has looked after the engine with as much care as I would have, so I was confident, all things considered, it would be in reasonable shape.

At first glance the engine seemed fine. The main areas in need of attention was some of the paint-work and the motion parts which were fairly dirty looking but thankfully, not rusty. Jack informed me that he had dutifully given the engine its end-of-day spray of WD40 but that had caused the steel parts to discolour badly and build up a thick film of unremovable crud! As usual his analysis was absolutely correct and I was just happy that the WD40 had at least prevented any visible signs of rust. I knew from experience that once rust takes hold the finish of the steel parts is ruined and the general appearance of the engine becomes rather sad. This rust problem reminds me of how many years ago my fairly new ML7 lathe was not checked for about a month. At that time my workshop consisted of a small wooden shed at the bottom of the garden. The midday sun heated up the felt roof and then at night it cooled down, the ideal recipe for condensation. Despite copious treatments of surface oiling the rust beat me and my treasured lathe was attacked. I can still see, many years later, the remnants of that rust as it created slight indentations in the slideways! Fortunately, I managed to get there before major damage was done. The indentations are only slight and I keep reminding myself that they act as good oil reservoirs but none the less it is there to be seen in all it's horror. These days my current workshop is part of the house and is North facing so the temperature remains pretty much the same and any temperature changes are very gradual. This is the ideal as rust will occur but only after months of neglect and the reason I use a quick spray of WD40 since this seems to protect and is easy to apply.

Back to the loco. The Wren was looking reasonable given the work it had done but the paint on the saddle tank had a few chips and scratches on it and was looking dull. I was not in the mood to start a major paint job but as the saddle tank is easy to remove and I had a tin of matching paint on the shelf I decided to give it a go. The job of spraying was fairly straight forward and was done quite quickly. As with most paint spraying tasks it takes longer to clean the spray gun afterwards than the actual painting. There was however the need for lining! Previously I had borrowed a professional lining tool which did most of the lines but due to my inexperience the corners had to be done by hand. I wanted desperately to design a new lining tool to ensure the finish was acceptable but despite my various thoughts I have not yet come up with anything. The lining was subsequently done using an old ink stencil pen I had from my early days in the drawing office and surprisingly it worked reasonably well with paint instead of ink. I used a permanent marker pen to initially outline the lining tracks so that the stencil pen could paint over the top. If only I could make a paint marker pen perform as well as the bog-standard marker my quest for a new lining tool would be over!

With the saddle tank finished it made the rest look worse than ever. I then decided that rather than go in for a major strip down to paint the boiler barrel and cab I would just touch up the chipped bits and put my efforts into checking out the motion and restoring the steel bits back to their former shiny glory. As the engine had done so much work it would also be an opportunity to check out the wear in the bearing surfaces. And so the motion was stripped down which is not a major task and takes but a few hours. Reassembly is another matter as I prefer to take time doing this. Cleaning all the metal parts is very time-consuming and despite soaking in various solvents the WD40 layers were there for ever! Of course I could use emery cloth and did so for the first coupling rod but even that took some hours and hard work. At this stage my appreciation of WD40 started to change and I vowed that in future another method must be found. By coincidence, I was in the kitchen and using a stainless steel cleaning pad, similar to wire wool of old and decided that maybe this would work on the loco. Notwithstanding the complaints from my better half it proved to be very effective and when used with a mixture of white spirit the steel parts started to shine once more and the pad showed no evidence of scratching unlike the course emery. I now have a few spare pads as part of the workshop essential cleaning equipment.

Having cleaned all the bits it was now time to inspect and either adjust or re-make the bearing parts. At this point I wish to state that the design of this engine by Ken Swan follows full-size practice especially in the case of the rod bearings which are based on a marine-type design. In most cases I reasoned that some judicious scraping and refitting plus some spacers would allow the bearings to fit as initially designed. So each bearing was separated from the rod and inspected for the tell-tale marks of wear grooves and then re-assembled to feel for fit and any slack. Bear in mind this engine has done nine years of constant hard work so I was expecting each bearing would need some considerable scraping and re-fitting. I even bought from Ebay a set of two pristine Moore and Wright scrapers for just this job. After a few hours checking, to my surprise I found that each bearing was just as good as the day they were first fitted! No visible wear grooves and no sloppiness. I merely had to re-assemble the whole motion. Now gleaming brightly I knew it was hopefully good for another nine years! Even the cast iron guides on the Hackworth gear were no worse than expected. These will always have some play in them due to the design of the small bearing surfaces but in terms of affecting the valve timing it was negligible. Finally I should like to re-state that whilst one has to make and fit these parts properly in the first place I think it is largely down to the basic design principles adopted by Ken Swan that have ensured a lack of wear. It is essential that the engine is looked after well and for this my thanks go to Jack Dibnah who has made sure all bearings are lubricated before and during running plus at the end of day cleaning down. As for using WD40, I am not sure. It certainly prevents rust and the de-watering properties work wonders if the engine is put away wet. I am trying various new treatments of oiling which basically consists of a cloth pad impregnated with a mixture of oil and thinners plus a touch of WD40 to drive off the water. Hopefully, this diluted WD40/oil concoction will protect but not discolour the bright parts so badly.

The loco is now almost ready for work, the motion has the new protection treatment applied, the paint-work looks reasonable and will pass for the time being plus the bearings are checked and good to run. It will need another boiler test before returning to the track so that will be the next task and then it's over to Jack's capable hands once more to give rides to the many visitors.

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