Hi all,
12V world of trains is my favourite, I admit it. Signals, decouplers, switches...simply wonderful!
But for a fast run with the children...nothing is faster to build than new PF tracks.

Solid,relatively cheap, one-piece rails, long curves...NO CABLES.

But, apart PF,RC and old 4,5V trains...there's no place for old 12V glories.

I've seen many 12V motors running at 9V, but I prefer to keep them running on 12V tracks.
9V motors and PF motors are great...but look ugly with their narrow wheels on 12v locomotives, plus no connecting rod can be used.

Since new PF motors are nice, fast and still keep the third central hole...here you can find a fast guide to adapt 12V wheels to PF modern motors.

I used three pairs of central 12V wheels. You can also remove the wheels from 12v axles, but be gentle and try not to break them.

Once you have the six 12V wheels, remove the plastic pin from four wheels and keep two wheels with the pin. These will be the central wheels.

Then you'll need to sacrifice two 6-long technic axles. This is the only tricky part of the whole process.

12V axles have a diameter of 4mm. so the two Tecnic axles diameter must be reduced to 4mm at both ends. I used a 4,5V old motor (lots of torque) to keep the axle running and a pair of pliers to model it as you can see in the pictures.

Once the two axles are ready (a bit of trial and error is required), slip the axles inside the motor and apply the 12V wheels without pin (they nicely lock on the axle). 

Ok, now get a plastic band and cut the first part (basically a triangle). You'll create a small plastic lid.

Now analyze a bit the PF motor. Near the two central holes there are two gaps, on both sides of the electric motor. These gaps can be filled with the plastic lid. This lid is important because it will help to keep the central wheels in place.

Cut the lid as shown and try to place the central wheel. It should be aligned with the other wheels already mounted on the axle.
DO NOT CUT the lid too much. It will disappear in the gap...and the wheel will come out. Keep it a bit longer and then adapt it.

Once you're ready with both lids inside the gaps, try to close the motor with central wheel mounted.
Once the motor is closed, try to remove the central wheel. You should hear a "click" and the wheel will come out.

Try again to put the central wheel in place. Another "click" and it should be firmly locked.

Now put all the rubber bands around your 12V Wheels and try to run your train.

For 7725,7740, 7745 this is an easy implementation. For steam locomotives 7710 and 7810 and diesels 7760 7735 and 7755 it is impossible to fit all PF equipment inside the locomotive cab...but you can simulate a 4,5v battery car or fit battery and receiver inside one wagon. 7720 can run on 4,5v directly :)

 "RED MOTOR" trains like 7727 7730 7750 and big 7777 Pacific...well, don't even attempt to replicate a red motor. The risk to break red wheels is too high, plus, the PF motor box will still be black...and won't  fit with red wheels. :) Run them at 9V instead. :)

In order to allow the connecting rods to work on steam locomotives, you obviously must turn the wheels by hand until all holes are aligned. Be careful on this alignment, otherwise connecting rods will fly everywhere!!! :)

Please don't break 12V motors and be careful with tools!
Have fun!

Davide