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Tuning Tips for the Aster 

Precedent Class 2-4-0 'Jumbo'


by Andrew Pullen, Aster Hobbies, UK



The Aster 'Jumbo' has proven to be a good and lively runner on the track and capable of pulling a decent load of 4-5 bogie coaches.  The general opinion is that the Aster 'Jumbo' will run well straight from the box in the case of a factory built-up model or after a successful kit construction.  My experience indicates that the Aster 'Jumbo' has no major vices. A little bit of adjustment may be needed and these notes indicate what may be done to give your loco an ‘edge’ over its peers.


1. Running-in.  A period of ‘running in’ under steam either on bench rollers or on the track with a light load will benefit your model.  Ensure the cylinders get plenty of oil during this period (see Tip No.2 below). 40 to 60 minutes in 2 or 3 sessions should be about right.  Check regularly for tight spots and any binding and correct.  Lubricate all moving parts regularly during the process.  If you are able to run-in your kit built chassis using a stationary boiler prior to fitting the loco's boiler, then so much the better since any fine adjustment to valves or timing can be more easily made.  Remember that long runs on compressed air can be very damaging to small live steam models.


2. Oil.  The Aster 'Jumbo' is very economical on oil.  In fact it can appear that there is insufficient oil getting through since loco and train may not be covered with the stuff!  However, be sure to leave some headroom in the oil tank when filling.  This will allow the 'displacement' process to get underway. During the winter months use of a lighter grade of steam oil may be wise.


2a More Oil.  If you are concerned that insufficient oil is getting through even after following the advice above, then try this idea supplied by Geoff Calver.  Place the oil filler cap in the three jaw lathe chuck and bore a hole in the underside of the cap going as deep as possible without breaking through the top and as large as possible without interfering with the threads - carefully measure the job before starting. Fill the lubricator full of oil and fit the modified cap. The air pocket in the cap will get the oil flowing.


3. Burner. It has been found that a better fire can be had with less tendency for the fire to self- extinguish if the wick tubes are reduced in height by 3-4mm and the wicks cut back by the same amount. I also found that the number of strands could be usefully reduced by 2 or 3 per tube from the recommendation. 


However if you cut back your wick tubes then you must increase the length of the fuel tank breather tube by a similar or greater amount. If you don't do this, then alcohol may flood from the wick tubes and a track fire will result. Lengthening the breather tube can be done by either soft soldering a brass or copper tube over the existing breather tube or slipping over a length of suitable plastic tube.


Do not forget to cut the extension to 45 degrees like the existing breather tube.  An extension of 5-6 mm should be fine since the tender alcohol sump is quite deep.  However, before carrying out this procedure, test your loco on the track with the original wick tube and breather tube arrangement. If all is well then disregard the above.


By the way, a full tank of alcohol should last at least 20 minutes (including lighting up) on a well run-in model.


4. Water. The axle driven pump is very efficient indeed and can fill the boiler from almost empty to over-full in a short distance and knock back boiler pressure very quickly too!  A steady run will repay careful application of the by-pass valve.  A just ‘cracked open' setting will give a good balance but do experiment with your model to find the best setting. I have found that the loco runs best with a fullish boiler so try to maintain levels without too much priming.


Secondly it is possible that some water leakage into the tender sump area may occur.  Water can find its way into the sump and cause a weak fire due to 'wet wicks.' This is because water may seep between tender top plate (9-15) and the front of the water tank.  A thin bead of sealant along this join will cure this problem if it occurs.


5. Pistons and Cylinder Block. Recent correspondence with my good friend Jerry Reshew of Diamondhead, Mississippi indicates that pistons pre-inserted into the cylinder bores as presented in the kit, may have been so done for good reasons. It is possible that the piston has been matched to the individual bore. If they are accidentally mixed up then performance may be affected.    I am checking this situation with Aster Hobby Co. Inc., but in the meantime please watch this point.


6. Smokebox Seal.. Although the kit instructions mention the importance of good seals to all areas of the smokebox, it is worth checking that factory built models also complies. Use plenty of sealant around the base of the smokebox, around the gap between boiler and smokebox and around the door opening and hinge. Any air leakage into the smokebox will spoil the performance of your model.


7. Steam Feed and Clack Valve. Input from Maelor Davis from Kentucky USA (but actually a Welshman) suggest that ensuring that the main steam feed pipe is pulled right up into the dome is a worthwhile operation. This ensure that only steam gets through to the regulator / blower unless the boiler is totally full off water. It may also help prevent that asthmatic wheeze that can occur when a little water gets drawn into the cylinders with the steam.  Maelor has also had problems with the clack valve (ball not seating, ball too small). Please contact Aster Hobbies Ltd if this occurs for free replacement parts


8. Petticoat Pipe.    Some comments in a recent G1MRA Newsletter suggest the mounting of a flared Petticoat Pipe into the lower end of the chimney. Results have been inconclusive. Customer’s experiences are welcomed.


9. And Finally….    Experienced runners will know this ‘tip’ but the tyro may not so let me remind you that it is a good idea to slightly crack open the loco’s regulator and blower controls as the machine cools down after a run. If you don’t do this then the controls may ‘freeze’. If you try to loosen them when they have ‘frozen’ then you may unscrew the regulator (or blower) body in the boiler. This can be problematic. Should you forget this ‘tip’ then don’t panic, relight the fire and the controls will magically ‘unfreeze’. This effect is all to do with the differential expansion of brass and stainless steel but can lead to a very irritating strip-down and rebuild if forgotten!


Appreciation for permission to reproduce Aster Tuning Tips for the Jumbo  on SouthernSteamTrains.com is expressed to Andrew Pullen, author © 2002 Aster Hobbies Ltd.


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