YZ 400 motor in a 490 frame????

Here's a weird one for the Group. I have a 78 YZ400 and an 82 YZ490. Right now the 400 is being used as a Hanger Queen (parts bike). However, the 400 motor would probably be better in the woods(smoother power, less vibe,quieter, 5 speed),and it has a clean DG pipe and silencer.

You can see where I'm going with this. Does anyone have experience putting that motor in the 82 frame. I haven't gotten down to serious measuring yet, but the two motors' cases look identical.

Also, how about the 82 490 carb on the 400 motor? I'm still looking for specs, but I think they are the same size.


the motors are different as the 400 has center port exh and 490 has side port exh.my yz400 has twin down tube frame and the 490 has single down tube frame.to monut the motor you will have to fabricate the down tubes on to the 490 frame.

Hi, Jim,

Once I had a chance to look at things it became painfully obvious this wasn't going to work!


the 1978 yz400 is easy to get parts from as earler stuff fits.ebay isnt bad as long as you stay in control.new pistons are aftermarket.my 1979 is gen yam only so parts are harder to get.if your 82 frame is complete look for a it or yz 465 as they run a bit better than the 490 (gas quality) and have 5 speed box.big decision is needed either build the 400 up and get rid of the 82 stuff or build the 82 up and get rid of the 400 stuff or build both.i just bought a 1981 it 465 of a 60 year olg farmer its striped for farm use but in very good condition will take it riding 12 august i then can tell you which i like better 400 or 465.




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