Dan,
I'll start by asking you what your goals are in dipping your toe in the p48 waters, echoing some of the concerns previously mentioned about the prototype accuracy of the MTH model. Those goals may have some bearing on the choice of the Railking mp15ac as your first model to convert to p48. While Bob is correct in that there is no explicit relationship between p48 wheel and track standards, and the accuracy of models employing them, there often is a correlation between the pursuit of accurate wheels and gauge and pursuit of more prototypically accurate models in general. So it is something to think about.
More importantly, I also think that there are a few better choices as a gateway model to get introduced to p48, from the perspective of ease of conversion. One of those is the Atlas sw8/9/1200 model. They are readily available on ebay at good prices, there are drop-in replacement wheel sets available, and starting from a 2-rail model will further simplify the entire process. The p48 conversion literally would take 5 minutes. The Atlas mp15dc would also be an excellent candidate for conversion, except they are harder to find in 2-rail. Even models like the Atlas gp9 or rs-1 can be converted to p48 with drop-in wheel sets. So there are many options out there.
All that being said, I'm going to presume that you are starting with the Railking mp15ac because you already utilize the DCS control system, and you already have the model in hand. Obviously, non-MTH locos would require conversion to DCS as well as to p48 if you wanted to use them with your current command system.
Setting those considerations aside for the moment, I'll list out the steps I think you will need to take to convert your locomotive to 2-rail p48 standards. Actually, most if not all of these steps would be the same for conversion to standard 5'-0" gauge 2-rail as well.
I've never owned an MTH loco, but I've read or heard things about the process of converting them to 2-rail, so I'm going to start with the presumption that your loco features the truck block with the captured axles. That means that the blocks can not be easily opened, and conversion will require pulling the wheels from the axles rather than removing and replacing an entire wheel set, axle included.
1) Figure out whether modifications to the truck block will be required for the conversion, due to the narrower gauge of p48. The simplest way I can think of to do this is to measure the back to back (BTB) dimension of the current wheels, and compare that to the back to back dimension of p48 wheels. If the BTB of the current wheels is less than or equal to the BTB of the p48 wheels, then no modification of the block will be needed. If the BTB of the current wheels is greater than the p48 wheels, you will need to then determine the overall width of the truck block and any external gears, and compare that to the BTB of the p48 wheels. If you have clearance, no modifications will be necessary. If the overall width of the block plus any gears exceeds the BTB of the p48 wheels, then quite a bit of modification of the block and placement of gears will be required to make the new wheels fit, which I would consider to be the most significant part of this conversion.
For reference sake, I measure the BTB on a set of p48 loco wheels at 1.100" +/- a few thousands. I measure the BTB on a set of 3-rail freight car wheels (all I have handy) at 1.025" +/- a few thousands. Based on those measurements, and if the 3-rail loco wheels match the freight car wheels, I don't believe truck block modification will be necessary.
If you move forward with the conversion at this point, then you will need to complete the following list of tasks:
2) Remove existing wheels and replace with p48 wheels, with all wheels insulated. The wheels are easy enough to get, but they will need to be sized to fit the existing axles, which may not be as easy to achieve. There are ways to mate up different sized axles and wheels, but this would involve something like fabricating new bushings or sleeves, which would not be an off the shelf component.
3) Remove the roller pickups, and disconnect the track power leads from the truck block and roller, to the motor or board, from the truck end.
4) Fabricate or purchase new power pickups, and figure out how to mount them to the truck block, while maintaining electrical isolation from the block to avoid shorting. Pickups usually consist of phosphor bronze wire or thin gauge phosphor bronze strips, in other words springy stuff, although other methods are available.
5) Connect new power pickups to the existing power leads, so that both pickups on one side connect to the truck block lead, and both pickups on the opposite side connect to the roller lead. If you cross things up, you will have a short. There are typical practices for which leads from which side are the hot and neutral connections.
That is an oversimplified list of the steps involved in modifying your locomotive. Obviously, any of the four steps can get complicated, and if truck block modification is required, the difficulty of the entire process increases exponentially.
In addition to modifying the locomotive, you will need to research what is involved in using DCS with 2-rail track. I know it can be done, and really I don't think it's any more difficult then reassigning the feed from the middle rail to one of the two outside rails. However, there may be specifics about which rail carries the signal or something of that nature, and specific arrangements like that may also dictate the arrangement of motor lead connections in the loco (again, I'm not an MTH or DCS guy so I don't know specifics). Also remember that 2-rail wiring must account for reverse loop polarity swaps.
To answer your other questions in the original post, my instinct is that you won't have to modify the truck block, a phone call to MTH might be required to find specs if you ultimately need them, and lastly I don't think a Stanton drive is the answer here, but I suppose it's a possible solution. Although you would just use the Stanton drive, powered as intended, with p48 wheels, and figure out how to mount it to the mp15ac chassis and connect all the various leads.
I think you need to consider your goals, and your skills and comfort level with this sort of work. Understand that there are potentially better choices for models to start with, although there are trade-offs between ease of conversion, and implementing or maintaining DCS control. Any 2-rail model, or even MTH 3-2 model, will be easier to convert with regard to the wiring aspect. Know that none of the above addresses cosmetic changes to the model like fixing the pilots and lengthening the handrails.
I hope that this summary gives you at least a preliminary idea of what will be involved. If you decide to go ahead with the conversion, I can follow up with more specific information on sourcing vendors and supplies.
Good luck!
Jim
