The Athearn Chassis

Using and Converting

Description

Athearn are an American model manufacturer specialising in US prototypes. The Americans rightly demand a well built, reliable, smooth and economic power unit for their locomotives, with virtually all US manufacturers obliging. The Athearn chassis is typical of the genré, albeit at the lower end of the market. Having said that, the power unit far surpasses anything we unfortunate British have to put up with from British outline manufacturers. The mainframe is cast metal. Centrally mounted is a large flat can 5 pole motor. The armature shafts leave each end of the motor, to which two very large brass flywheels are attached before reaching the first of two universal joints. From these UJ's, a drive shaft is linked to another UJ on the top of the bogie. The drive shafts are fixed at one end and fit into a larger diameter keyed tube at the other. This accommodates any required lengthening or shortening of the drive shaft as the bogie rotates or swivels. The bogies are of a split frame design with wheels to the RP25 standard. A system of gearing allows all wheels to be driven while the split frame chassis allows all wheel pick-up.Underframe detail such as fuel tanks is also in cast metal. The result is quite a heavy, smooth running unit. Normally one has to buy the complete locomotive and throw away the body. However, this is not as bad as it seems. The last chassis I picked up was an SD9, a Co-Co locomotive suitable for the CIÉ 071 and NIR 111 Class. This cost all of £23.95 at the time. Compare that to a typical Lima or Hornby effort with its three pole pancake motor at twice the price, and this has been imported from 3,000 miles away!

Using the Athearn Chassis

For Irish use, a number of chassis can be used.

071/111 Class. Athearn SD9. This chassis virtually just slots in. All that needs to be done is to remove the the coupling protrusions at either end of the frame. A suitable mounting and fixing point will have to be made.

B121 Class. Athearn SW1500. This chassis is another that just slots in after removal of the coupling protrusions. A suitable mounting and fixing point will have to be made.

NIR 101 Class. Athearn F7A. This chassis is another that just slots in after removal of the coupling protrusions. A suitable mounting and fixing point will have to be made.

201 Class. Athearn SD45. A bit more complicated this, the chassis has to be lengthened or a suitable conversion can be purchased from Eric White.

Other locomotives, such as the A Class, B141/B181 etc. can also use the Athearn chassis and indeed some people have done so. However, I have pursued a different route with these locomotives although I will post details as and when.

Converting to a Different Gauge

One of the beauties of the Athearn chassis is its bogie construction. As previously mentioned, the bogie is of a split frame construction. To achieve this, Athearn have used a plastic axle with the drive gear mounted on it. Into this plastic axle, two metal stub axles carrying the wheels are inserted. To alter the gauge, in my case to 21mm P4 standard, you do the following. Pull the stub axles out of the main axle. You will now have to make new longer stub axles from 2mm diameter silver steel rod, from Eileen's Emporium for instance. The new stub axles are about 10mm long. The Athearn stub axles are 3/32" diameter. You will have to use a conversion sleeve to increase the diameter. Such a sleeve is available from Exactoscale as part number GB016. One sleeve per stub axle will be required. The wheels will be of your choice dependent on gauge/standards. One point to consider here is the method of power collection. The Athearn wheels are solid metal discs, power transfer is through the axle bearings. I decided to use the same method for simplicity. However, most replacement wheels are plastic centred. If you use these, you will have to supply a link from the tyre to the axle. Another solution does exist in the form of the solid disc wheels used in the Black Beetle motor bogie supplied by Branchlines. Upon request, I received a set of wheels only, with 2mm diameter holes turned to the P4 profile. These are an interference fit and have to be carefully pressed into position on the axle whilst getting them perfectly square.

Do take care here, you don't want wobbly wheels. Having done this, the sleeves are fitted to the stub axle tight up to the back of the wheel. The new assembly is then offered into the bogie axle. It will also be necessary to insert some form of spacing washer between the back of the wheel and pick-up plate to prevent the axle bearings drifting out of the pick-up plate. Some slight length adjustment may be necessary to achieve the correct gauge in conjunction with a suitable back to back gauge. One can then test the regauged locomotive. I have not experienced any problem with this method and the same principle can be used for EM gauge. The slight vertical play in the bogie should suffice as a form of compensation. Again, I have not experienced any problem in this area.

Altering the Length of the Chassis

With certain chassis/locomotive combinations, the chassis length has to be altered. Such a case is the IÉ 201 Class/NIR 208 Class, where the SD45 chassis has to be lengthened. Altering chassis length is reasonably straightforward. With the bare chassis and body in front of you, measure the length the chassis has to be in order to fit within the body to a suitable securing point, bearing in mind the bogie centres of the prototype. Make a note of this length. Remove the motor, bogies and drive shafts. A cut will have to be made across the longitudinal chassis members and some suitable brass angle section let in. It is best if you can keep the motor unit and one bogie end complete. This means you will only have to make one longer drive shaft. Having decided on where to cut, use a junior hacksaw to separate the chassis.

Now, position the two parts of the chassis to the new required length. You will be left with a gap between the longitudinal members. Measure this gap and allow some 20mm extra at either end. This means your brass angle section will be the new length plus 40mm. In these 20mm overlaps, you will have to drill two holes large enough to accept some 10BA or similar bolts. When you have done this to each piece, offer them up to the chassis. Mark the chassis where these holes will appear. Drill the matching holes through the chassis. Now it is a simple case of bolting the pieces together with the use of some Loctite or similar to secure the nuts.

Reassemble the motor and bogie units. Now get some plastic tube of about 3mm diameter, Plastruct tubing is fine, and cut a length that will fit the gap between the UJ's. Remember to allow a little extra for bogie movement. When satisfied, a small strip of Plasticard can be used to make the keys that engage in the key ways of the UJ's. Reassemble the whole unit and test. One lengthened chassis! Shortening is a similar process in reverse, but make sure the chassis can be shortened to the length you require first.