Can anyone tell me if this is an RT2 MX head and barrel.
No proper numbers on either part , just #400 on the head ,no decompressor , there's a reed valve and adapter and a rather sturdy exhaust spring holder. 

Yes does look like it. Now im jealous 'as'. Need pics all around & one over the top but yes its conclusive in my mind. Funny how things improved over the years & the reed block is the same as a YZ80 from about 1980 even though numbers might change--still same as RT2 DT2 & all that. YZ80 had the nose where the reeds close sharpened up a bit pointy rather than blunt nosed but nothing fancy. I just noticed the RT2 flange carb mount as original was rubber push in carb type. What bore size is it on. Head fins should be quite high on those & cylinder fins quite wide & square-ish. Exhaust flange shape is a clue too.
Had a look on Partzilla just now & RT2MX in "72 is 10V for reed block & 1980 YZ80 is 10V also.

Photos of a NOS RT2mx cylinder I had -  and still have a couple of used heads. Photos attached but just wondering where the 400 is on the head?

Yes it is . I gave it a good soak and clean as it was scabby picked away at the number and there it is .
Only just it's a 2 not a 4 and i can just make out 32200 . Nothing on the barrel though.
I have scraped the clay and oil off the motor. It's in a state . The tacho has a plastic blank with a proper wire routing clip fixed on top. It also appears to have been black crank and side cases.
I think the outer cases are off an enduro though as the have Yamaha embossed on them and i think the bolts holding them on are from a Honda ( 8mm hex )
I think it has the wrong piston in though. Two rings and it has no windows . I think it has the initials JL cast on it on the pin boss.
Maybe aftermarket .
Oil pumps gone, i think that's due to enduro cases being on and the clutch has too. I have a spare clutch assembly for the 360 so that's okay. I imagine it would be pre mix on an MX bike.
Generator end crank taper has seen a broken woodruff and some jerk has had a hammer on the threads.
The stators seen better days but i have spares. I also have two spare back plates . The one on the motor has three coils .
I would have thought two for that but i haven't looked at any details. Engine numbers there and it starts RT1.
I'll measure the bore RT and take more pics. Also, the reed to carb adaptor has been put on by the same person as the outer cases. The Honda and Allen screws are the give away 
Dave

DT2MX looked the same. I had one new & my boss had the 360. DT2MX will only have the 4 long bolts & not the 8mm studs on the head. The mag cover on both motors will be a slim one as use a small rotor mag on 250 & cdi on 360 & painted black. Sounds like you have a complete motor but interesting they've fitted the flange type carb manifold. Possibly the rubber one was stuffed so fitted that with a small rubber carb mount. Anyway--doesn't matter, wish it was mine haha.

I do think there's been a degree of pissing about with the extremities on this. It's possible someone's tried to convert it to road use and that's how they've spun the rotor . Too heavy , the powers come in and sheered the key.
It would need a cargo plane to land at your place RT as the postage would be a little hefty as is the motor.

 


Like this then ?

You posted photos while I was typing - so deleted what I typed. Looks like aftermarket weight added to internal rotor ignition. Any more photos from side?

No shifter shaft has RT2 type cover with the nipple .
Yamaha logo stamped in not standing proud.

Hahaha, we're typing over each other.
That's an engine i just looked for which is for sale here in the UK . I was answering a suggestion by RT325.
£700 or near offer it's up for .
I'll take some pics tomorrow.