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Tuning Tips – Aster LNER A3

by Andrew Pullen, Aster Hobbies, UK


My Tuning Tips for the Aster Precedent Class 2-4-0 'Jumbo' proved very useful for kit builders and owners of that particular model and so I thought it might be useful for customers to have something similar for the new Aster A3.


These notes will be updated from time to time as more information and experience comes to hand. You are invited to add your tips and ideas for the benefit of all.


Please keep in mind that tips for both kit builders and for owners of ready to run models are included below. 


1.  Wicks. As supplied the wicks may not be entirely suitable for supplies of the poor quality ‘Meths’ supplied to the UK market. Generally wick replacement with either traditional material or the newer carbon fiber or mineral wool materials may be desirable. With the right wick, the boiler should steam like fury.  Ultimately some reduction to the height of the wick tube maybe be desirable – your comments appreciated.


2.  Oil. I have found that the use of the oil pressuriser is only required, if at all, very occasionally if a medium grade of oil is used. If the loco sounds a little ‘hoarse’ then a quick on – off application of the pressuriser gets oil moving again. Remember to close the regulator when using the oil pressuriser.


3.  Loco / tender coupling.  The coupling bar between loco and tender is very rigid and may, on a bumpy track, cause the tender to lift. To correct this I suggest the careful enlargement of the slot in the tender draw beam by 2 mm. Only the top edge needs to be filed carefully. Alternatively fit a new drawbar made of a thinner material.


4.  Regulator freeze.  Experienced runners will know this 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.. Should you forget this ‘tip’ then don’t panic, relight the fire (ensuring there is water in the boiler) and the controls will magically ‘unfreeze’ when temperature is up to operating levels. 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!


5.  Cylinder beats. My own production example and other production models I have seen working clearly demonstrate the ‘six beats to the bar’ of a three-cylinder loco. If you can only hear four and two ‘whooshes’ of steam then perhaps the valve on the inside cylinder may have dropped-off the port face. Too much boiler priming may push the valve off but it should snap back quickly.


6.  Water feed union.  I like to run my Aster A3 close coupled to the tender. However, the water feed union part 10-11 may foul the tender. I suggest exchanging part 10-11 for LN5 on the water return pipe 10-38 in the tender tank. Reference to the drawings makes this clear.


7.  Dummy Ejector Pipe.  Where this pipe crosses the smoke box it should be painted black. A small point but worth doing.


8.  Wheels.  In reality the wheel rims and hubs are black with a fine white line separating green from black. Please refer to a photograph of an A3 in LNER livery. Aster Hobby Co Inc are very proud of their polished rims etc. I leave it to you to decide if you make this adjustment. Tender wheel rims are plain black.


9.  Notching-up’. A number of runners (including myself) have found that the Aster A3 works best with the reverser about three full turns back from full forward gear. Clearly some experimentation with your model is required but having seen when building a kit how much valve travel occurs in full gear, some reduction seems very sensible and gives more even beats and a smoother performance.


Several kits have been successfully built and the following points should be noted


1.  Drawing two is drawing three and vice-versa.  Labels will be found in the back of the instruction book to correct this.


2.  When fitting the crosshead to the piston rod, be sure to fit the slide bars to the crosshead first. If you follow the instructions you will find it difficult to do this after you have ‘lock-tighted’ crosshead to piston rod.


3.  Extra care taken on getting the valve timing right will be rewarded by a great running loco.  The part of the construction is the most challenging but the drawings and instructions are quite clear. Near enough is good enough does not apply to this section. Get it right from day one!


4.  To help in this regard, make yourself a small protractor from card (or clear plastic) with an angle of 34 degrees. Place the chassis on a flat surface and using your protractor get the return crank angle set precisely. Time taken here will be rewarded later.


5.  Boiler. Having fitted the regulator and blower into the boiler, be sure to fit the dummy back head in place before adding the various back head fittings. A dry run with parts will establish the correct order of assembly.


6.  From Jerry Reshew of Diamondhead USA.  In order to get a mirror finish on both the cylinder port faces and valves themselves, I switch to 1500 grit paper after doing the requisite polishing with the supplied 1000 grit paper. About 100 strokes of wet and light pressure should really give you a superb finish. The absolute mirror finish really does make the locomotive run beautifully in the case of the Mikado and the Jumbo.


7.  When assembling the exhaust steam pipe from inside cylinder 3-24, to exhaust steam pipe 3-9, it may appear that the blast nozzle 3-25 will be out of alignment. Do not worry; this will be corrected in Section 5 when part 5-31 is fitted.


8.  The lengths of the flexible tube (BT5) is reported to be reversed in the drawing. The feed should be 180mm and the return 160mm, please check this

9. Most kit builders will agree that the Aster A3 is one of the best Aster kits for ease of construction and accurate fit of parts. However the tender axle guards can be very frustrating.  Small spigots attacked to the dummy springs may not locate properly in the holes provided in the tender frame. Either file of the spigots or enlarge the tender frame holes (3.5mm drill).


10.  Let me re-emphasize the important note on page on page 24 of the Aster A3 Operating & Instruction Manual. The operating of any small model under compressed air is for valve setting as described in the manual and should be applied for the minimum time possible.  The use of compressed air for other proposes is positively discouraged. Unlike steam, which has a lubricating effect and will draw oil into the flow, compressed air will blow out any lubricants in the steam ways, valve chests and cylinders. Damage caused by over use of compressed air will not be covered under warranty.


Appreciation for permission to reproduce Aster Tuning Tips for the A3  on SouthernSteamTrains.com is expressed to Andrew Pullen, author © 2002 Aster Hobbies Ltd.


A3 Tender Coupling Modifications

a suggestion from John Garrett


Loco / tender coupling.  The coupling bar between loco and tender is very rigid and may, on a bumpy track, cause the tender to lift. To correct this I suggest the careful enlargement of the slot in the tender draw beam by 2 mm. Only the top edge needs to be filed carefully. Alternatively fit a new drawbar made of a thinner material."


If you go the enlarged slot route be prepared to make a new coupling pin.  The smaller diameter portion of the pin will have to be moved up 2 mm so that the bar does not slide off the pin.  This may present a problem for those who do not have access to a lathe.


I had trouble with one of the copper tubes twisting when tightening the compression nut.  This would not have happened if I had used a drop of steam oil on the tube and nut.





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