Hi All, Some time ago I came into possession of some Donnerbüchsen or Thunder Boxes, Märklin items 4313,4314 and 4315 which were no longer usable as the axle bearings had worn out causing the wheels to rub on the bottom of the coach chassis, making the drag on the locomotive so great the engine stalled and burnt out the motor. This train was used in a display where it was unattended for long periods of time. I repaired the locomotive for the owner and the coaches were put into my to do basket to repair when I had some time. Living in Australia the options to get replacement coach chassis with the correct coach lettering is difficult and time consuming so I decided to see if I could do a repair to the coaches as a challenge, nothing ventured, nothing gained as the saying goes. Lubrication before Use Warning On the box Märklin suggest oiling the car wheels before use but I prefer to use HL657 White Grease with Teflon marketed by Woodland Scenics as I don t get oily deposits on the wheels and my wheels remain much cleaner for better operation. Link to my Lubrication Article I must say that this is the worst case of axle bearing wear I have seen. Before running any rolling stock I heed Märklin s suggestion and lubricate the items before use. My rolling stock is run on a regular basis and over a twenty year span I have never had any problems. The Problem Without lubrication the axle had cut the axle bearing down (red arrow) and the wheel interfered with the coach chassis (orange zone) You can see that there has been some attempt to fix the problem by filing the slot for the wheel flange but the wheel interfered with the coach chassis also in the yellow zone. http://members.ozemail.com.au/~rossstew/rms/marklin.html 1
The Problem (continued) Looking at the end of the chassis with the wheel fitted you can see that the wheel axle centre line (orange) is further down towards the chassis and the moulding for the wheel bearing centre line (red) is above the axle Even with the filing modifications the drawbar pull was well over 30gm for the three coaches and with a small locomotive the effort at slow speeds was too much causing the locomotive to stall. The Challenge I wanted to be able to raise the axle centre line back to the centre line of the moulded bearings without any visible damage to the coach chassis. New bearing surfaces would have to be inserted to prevent further wear. Drilling was not possible because I couldn t maintain a straight angle to the bearing axis and finely the wheels must have free movement. As a last challenge I wanted to do this with simple tools that I had in my tool box. Warning: - You undertake the following modifications at your own risk. The cutting of small parts and heating plastic is required. The Solution After much thought the solution fix proved to be quite simple to do. In fact the planning took me longer than the implementation. I first measured the wheel axle length at 24.4mm For the positioning of the new bearing locations I cut a 1.5mm diameter brass tube to a length of 25.0mm Each end of the tube was chamfered. 24.4mm 25.0mm http://members.ozemail.com.au/~rossstew/rms/marklin.html 2
The Solution (continued) Cutting Bearings I needed to be able to cut very small lengths of the 1.5mm diameter brass tube safely for the new bearings. I chose a 100mm length of 8mm square wood to aid as a cutting jig. Using a pin-vice with a 1.5 mm drill I drilled the hole at one end of the wood to a maximum depth of 2mm as shown in the cross section below. I tested the depth of the hole with a line marked on the brass tube until I obtained the correct depth. Next I drilled a 1.0mm hole on the edge of the 1.5mm hole to allow extraction of the small brass bearing by inserting the drill back into the 1.0mm hole to push the brass out after it had been cut. 1.5mm Hole 1.8-2.0mm 1.0mm Hole The flexible shaft of my Dremel is held in the vice with a cutting disc to allow both hands to hold the cutting jig and brass tube. First I chamfered the end of the brass tube then inserted it into the hole in the wood. Holding the jig and brass tube as shown above I positioned the wood on the left side of the cutting wheel then carefully cut the tube. I repeated the process until I had made twenty bearings. Using a round needle file I then de-burred the cut ends as this will be the bearing surface with the needle point of the axle. http://members.ozemail.com.au/~rossstew/rms/marklin.html 3
Bearing Hole Position I inserted the 25mm length brass tube as shown above. The wood spacing height of 4.65mm raised the new bearing location back to the centre line of the moulded bearing in the chassis. As you can see the wheel holder has been bent quite some distance and it took some pressure to insert the brass tube. The Scary Part This is the point of no return as heat will be applied to melt the plastic. With the chassis on a flat surface I squeezed the wheel holders together as I applied my soldering iron (300 deg.) I made sure I heated both sides of the brass evenly until the chassis had resumed its normal straight position on the flat surface. It is most important that the brass tube is parallel to the chassis. Once the tube has cooled down it can be remove from the chassis. Bearing Placement I inserted a brass bearing into the new holes, chamfer end first then fitted the wheel to see how tight the axle was in the bearings. In all cases I needed to insert the bearings deeper into the chassis and to do this I used the soldering iron with a small tip and applied heat direct to the bearing being careful not to move the bearing sideways. As luck would have it, the excess plastic came out of the hole in the brass tube which I removed with a 1.0mm drill. I repeated testing the wheel axle to ensure I had a little side play. With the tube holes clean the wheels could spin very well. http://members.ozemail.com.au/~rossstew/rms/marklin.html 4
Final Results I was very pleased with the final results as the wheels spun very well and there wasn t any visible damage to the outside bearing detail on the chassis. With some HL657 White Grease with Teflon applied to the bearings the wheel spin is very smooth. I think I can say I have resurrected the three coaches for future enjoyment. As always enjoy your hobby. http://members.ozemail.com.au/~rossstew/rms/marklin.html 5