Zamac Frame Repair
As mentioned on several pages of this site, many of the A1G motive power main chassis or frames are made of Zamac, an acronym that means Zinc Aluminum Metal Alloy Casting. The metal is about 95% Zinc, 3-4% aluminum, and much smaller amounts of other metals such as iron, cadmium, and copper (impurities).
Usually, these castings are pretty sturdy and stable. However, corrosion of one or more of the "impurities" in the alloy can cause the casting to swell and crack. This is because the result of the corrosion is that the volume of the "impurity" and its corrosion increases and, being that zinc and aluminum are not very ductile, the casting swells and cracks instead of accomodating the increased volume.
Of course, once this occurs, the dimensional properties of the casting are altered and this can be disastrous with a casting as small as those used in N scale models. There is usually only one solution offered by most authorities in the hobby - replacement of the casting. This is because the conventional wisdom has always been that the condition (swelling and cracking) will continue once it begins so that any repair will be temporary. While theoretically this makes sense, I have found that it doesn't always hold true.
If the casting is disintegrating into powder, then I would agree there is little to be done but to find a replacement. Or, if the casting is distorted to such an extent that, even if the cracks are repaired, restoring it to useable dimensions is impossible, replacement is the only solution. For example, I have an 0-6-0 steamer frame in this condition. It is severely bowed and fragile.
In most instances in my experience, however, I have found that it is possible to both restore enough stability to the casting and restore the dimensions to make the casting useable.
Identifying a casting suffering from "Zamacitis", as I call it, is usually easy. There will be cracks at a minimum (actually, this would be relatively fortuitous) and usually distortion. Sometimes the cracks will be fairly subtle and you might have to look closely but, for the most part, they will be readily seen. Here, as on the E8 page is the image of a pretty badly cracked E8 frame:
Although it doesn't really show in the picture, this frame is also elongated and warped along the horizontal axis.
Here is the procedure I use to repair frames such as the one above:
Ideally, I like to completely remove all the other parts from the frame, degrease it, and then apply superglue to all the visible cracks in the casting. I use ZAP super thin CA by Pacer Technologies, but other types will work too. However, if removing parts causes pieces of the frame to also be removed, I keep the superglue at hand and reattach the pieces of the casting immediately. This is easier than waiting until the frame is bare and then determining where all the pieces go (although this is the way I did it with my IHB 0-8-0 years ago). Also, if a break is fresh, the superglue will hold before any contamination gets to the joint. Of course, there is always a caveat. If the frame breaks into fairly large chunks (as my original E8 frame did), it is better to wait so you can get the pieces aligned as close to the original configuration as possible.
Superglue seems to work particularly well for this job. It clings very tenaciously to the almost crystaline surfaces of the broken Zamac. In fact, it even works very well between two Zamac surfaces that have been filed smooth. More on this later. Getting superglue into every crack, even the tiniest ones, is the key to stabilizing the casting. Here I will mention the generally accepted idea that repairing one of these castings is temporary. As I stated above, I repaired my IHB 0-8-0 many years ago (25?) and it is still going strong today. Same with my original E8 and that repair was longer ago than the 0-8-0.
OK, after dousing the casting with superglue (and allowing the superglue to cure), it has to be restored to dimensions that will at least allow the locomotive to function again. I have never tried to be too exact with this procedure. I just file the casting so it will fit back into the shell easily and allow the mechanism to work smoothly. This last operation is more critical with steamers than diesels because of the more complex drive. However, even with these, I have found as long as I file the slots for the drivers and the idler gears so they just slide in easily without too much slop, and get the surface the driver retaining plate fits against flat, the locomotive will run acceptably smooth. Of course, it is always a trial and fit situation since no two frames will be warped exactly the same. But it can be surprising how little filing may be necessary. There will be times the opposite occurs. I have some E8 and C-Liner frames that were so elongated that I thought I would never get them shortened enough to fit back into the shell again.
Some specific situations:
E8s and C-Liners:
These frames, in addition to cracking, usually elongate to the extent that sometimes the shell will actually be cracked or the frame will be stuck in the shell. Getting the frame out can be an adventure in itself. A combination of pulling, prying (not too hard on the shell), and coaxing may be necessary. After its out and the cracks superglued and/or the pieces fit back together, file the frame evenly at the front and rear until it fits into the shell easily without binding. Shortening at both ends will retain the original relationship between the shell and truck positions, at least close to the original. You may also have to reduce the width of the frame. Caution will have to be exercised in the area of the motor because the frame is very thin here.
Two other things. The protrusions that go into the slots on the lower part of the shell may also swell or elongate and may have to be filed down to fit easily into the shell openings again.
The two ends of the frame on either side of the fuel tank area may bow up in the middle leaving a kind of wavy bottom. Usually this isn't severe enough to cause problems so they can be left alone. On my original E8, however, I did end up having to mill the rear surface flat again so the worm and truck were relatively perpendicular again.
0-8-0s, Pacifics and Mikados:
These frames are similar and affected alike. The frame usually warps so the surface for the driver retaining plate is concave instead of flat. Careful filing is required to get it back to an acceptable flatness and still allow room for the driver axles. The slots for the axles may have to be filed a little deeper. It's not really that hard to do though. I file the slots, put the drivers into them and set the frame and drivers on a piece of track to make sure all the drivers contact the rail while bottoming in the slots. After the worm/housing, gears, and drivers are back into position in the Pacifics and Mikados, I put the assembly on the track and turn the coupling attached to the worm shaft with a screwdriver of the correct width to ensure that there is no binding in this part of the mechanism. This can't be done with the 0-8-0s since the worm is on the motor shaft so the motor needs to be reinstalled and run at low speed to check for smooth operation.
On the Pacific, the front extension of the frame for mounting the cylinder assembly and pilot may warp so that it is angled down toward the front instead of being parallel to the rest of the frame. This can be left as is if not too severe but if it has elongated so the main rods can fall out of the holes in the cylinder assembly, it will have to be cut off, shortened, and refit to the rest of the frame. Elongation can be determined by installing the shell onto the frame after the cylinder assembly is in place. If the steam passage molding on the boiler is rearward of the molding on the cylinder assembly, elongation has taken place. I cut it off right in front of the area where the driver retaining plate attaches, file it shorter (note how much to get it lined back up with the boiler molding) and reattach it with superglue. This is where the superglue seems to work well even though the surfaces may not end up exactly matching. I have used epoxy here too but I used only superglue on one and it is fine.
The frame in the area of the motor mounting in these locomotives is very thin too so use caution when working here.
That's about the extent of frame repair and you will probably want to repaint the frame semi-gloss or flat black after completion. This is especially true of the steamers as some of the frame is visible after the boiler is in place.
If you should decide to replace the frame in a steamer instead of repairing
it, I know there have been replacement frames made by Aztec and, I believe,
N Scale of Nevada. I don't think they are currently being made though, so
you will have to look for them either at meets or on ebay. I have also seen
original frames on ebay, usually included in parts or "junk" auctions.
Of course, in this situation, you want to be sure you're not buying
another frame with "Zamacitis".
Pick a page to go to:
|EMD E8s||FM C-Liners||IHB 0-8-0s|
|Alco RSC-2s||EMD GP40s||USRA Pacifics (4-6-2s)|
|Plymouth WDT Diesels||0-6-0 Steam Locos||EMD SD45s|
|USRA Mikados (2-8-2s)||0-4-0 Locos and Tenders||SW1500 Cows and Calfs|
|Atlas Model Specific Issues||Atlas Locomotive Disassembly||The Rivarossi Motor|
|The Mehanotehnika Motor||Atlas Locomotive Reassembly||AIG Locomotives Around the World|
|The Treble-O-Lectric Main Page||Treble-O-Lectric Locomotive Service||Treble-O-Lectric Documents|
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