FPJ Motomaster (Diesel) is a good toy, but I don't think those 4 limbs worth $250...
So this is a tutorial to use existing Hasbro cars to replace them, to save money (of course), to get the old toys from storage, and to get some DIY fun.
This tutorial is inspired by pjx1985625 on AC (
http://bbs.actoys.net/read.php?tid-1863499.html). The original post gave me the idea, and I improved some issues (like using rubber band, part loose, need to modify FPJ part) using Lego parts.
The target is easy, secure enough for any pose and don't change anything in FPJ or Hasbro robots.
Hands are:
Generation Sunstreaker, Sideswipe
Legs are:
TFP vehicon and Knockout (I choose Knockout because it's small and cheap, Knockout is the only one I plan to repaint, since the color doesn't match)
Shoulder parts
1) As show below, since 1 and 2 don't match, use the 3 from lego parts (It's a very common connector part from Lego bionicle heroes).
2) Cut the part a little and put into Sunstreaker's hole as shown, then the FPJ should part can be connect very tight and secure.
Hands
As shown below,connect the red circle on Sunstreaker to Lego parts, it's also fit perfectly, and it makes sure Sunstreaker's legs (Stunticons's arm) won't split.
Also connect Stunticons's hands.
Then the 2 arms are ready
Now comes to legs. It's a little more work, need to drill 3 holes on each Lego boards, so it can fit on Motomaster's part. Then secure long screw on each board, as shown below. Connect 1 to 1 and 2 to 2. Those are the places I found can fit very well and won't be loose after combination.
Then it's done. Let me show some end result pictures here. (The only thing need to do is repaint Knockout, which I might do it later.)