help to convert mth 2 rail premier daylight to 3 rail

It would be cheaper and easier to take the loss and sell it.  You can’t modify the wheels to deepen the flanges.  It requires a complete chassis change, if you could find one.  And some versions of the same loco (Proto 1 to Proto 2 and 3) can have a different gear ratio which won’t mate with the drive motor.  Most Premier diesels can be changed because the wheelsets are removable, but steams are different.

I think the conventional response would be to sell the engine and find a 3 rail version of it. You could in theory try to replace the wheels with ones with deeper flanges (I know MTH on their 3/2 engines had scale and deep flange wheels you could swap in).

One question, have you looked at the min radius for the 2 rail engine? It could be it requires greater than 36" radius curvers (72" diameter) and the flange is not the issue. Running an engine on a smaller radius/diameter than it is designed for can cause derailments on track and switches. I looked it up and if I have the right model, it says 42" radius curves, which would be O84 diameter, so your O72 would be too small.20-3300-2 is the model I found that seems to match your description.

I seem to recall that with their 3/2 engines, MTH offered deep flange wheel sets you could swap out, but if I have the right engine I don't think that would help. If I am not looking at the right model #, look up the model number on your engine and see what the min is there,I suspect it is going to be 42" radius as well, the ps 3.0 model had the same specs.

GS drive blocks for 3 rail is available thru mthpartsandsales.com ….won’t be a cheap swap, but doable, ….you can leave the pilot truck alone, as it will navigate MOST 3 rail hi rail track,….the trailing truck would require hi rail wheels, or complete truck swap,….again, available,……tender trucks just require axle/wheel swaps, and adding coil coupler, if desired,…wiring for coupler should be present. Locomotive wiring requires some finagling, but again, doable…,….I’ve performed dozens of these swaps. Again, not the cheapest game in town, but doable,….all GS drive blocks have same gear ratio, 2 rail or 3 rail,….I’ve swappped a couple GS’s for folks,….

Pat

I'd love to see a picture....

Like Pat, @harmonyards said, a chassis swap is doable. It'll cost ~$150-200, but you can recoup some of that selling the two rail chassis. The 3 rail chassis is bolt in, so if you have a screwdriver, 5mm nut driver, and two hours of time you can do the swap on a workbench.