I am in the process of a motor swap project – stuffing a YZ400F motor into an Aprilia RS50 chassis and I have some questions and concerns that I thought some of you might be able to address for me: I bought the motor used and right now it is torn down except for splitting the cases. I am awaiting a rebuild but I am undecided about a few things. Everything loks pretty good and I haven’t found any problems. I plan on replacing most of the seals and bearings as well as the piston and cam chain but is there anything else in particular that I should be weary of on this motor? I have plenty of experience wrenching on two-strokes and larger, multiple cylinder four strokes but this is my first thumper rebuild. As far as pistons go, are any brands far superior? I am planning to go with a Weisco 12.5:1 kit but am considering the 13.5:1 kit. My primary concern is reliability because this motor will be run on the street, is the extra power from the 13.5:1 kit worth it? Does the 13.5:1 kit really need better than pump gas? Anything special to look for when examining the head and valves? I will need the motor to charge a small battery and power a few lights. I was given a stock WR450 flywheel from a friend and was hoping to be able to use it and a WR450 stator to run the electrical. Are the WR450 stator and flywheel compatible with the YZ400F motor? Are any special changes needed (timing, etc.)? The exhaust system will be custom and most likely based on whatever I can find a decent deal on at the time I am ready to install it. I don’t care about it being loud (actually I prefer it) but are there any systems that don’t hold well under stop-and-go traffic or extended high RPM highway usage? Which systems don’t seem to be bothered as badly by reshaping the header and midpipe? I do plan on using some kind of auto-decompression exhaust cam but am unsure about if I want to go with a YZ450 unit or a hotcams unit or hotcams intake and exhaust cams. Any input on what would be best for street use (I want lots of low end hit without losing top speed)? Since the motor with be covered up with beautiful Italian fairings, I will not be able to get to the choke and hotstart knobs. Do you know of any kits to relocate these to the handlebar? Thanks a lot !!!