MX250 Piston - Gudgeon Width Variation?

[mx250]

I'm playing mix and match (well I thought I was  ).

I've got one running MX250 donk and a not-yet-running donk. To trial the not-yet-running donk's gearbox I thought I would swap the top end to give the  not-yet-running donk a try out.

Apparently the running donk has a YZ D or E piston (judging by the cut out at the back). But it's opening for the gudgeon is 36mm with a 22mm little end.

The other motor is 22mm little end with a 23mm opening in the piston for the gudgeon. This is what I would expect.

But the runner seem to run okay with the 36mm opening and 22mm little end. I would have thought the little end bearing would move across the gudgeon pin causing all sorts of strive.

Whatcha reckon Brains Trust - run it  .

(The camera battery is flat - I'll take pixies if its too confusing an explanation.)

[Iain Cameron]

Standard piston? Ive never seen one with a gap that size, How is the barrel oval? [ possibly later mod piston]

[mx250]

Standard piston? Ive never seen one with a gap that size, How is the barrel oval? [ possibly later mod piston]

It looks a standard Yammy piston but I don't know the history of the motor.

I've assembled it and it seems okay. It was running 'as is' and I won't be running the motor long - just to go up and down the 'box and accelerate it hard in each of the gears to try them out. I'll just run it and keep an ear out for the motor . It was running okay. I can't explain it. It not as I expected it to be.

[Freakshow]

the one on the right is a Wiseco piston, it look like a 464 stamped on it which is the same as the one i use the 234 they suit the motors from 74 to like 79 so there are changes in the 2 series.

the section between the walls is the same if you look on the section next to the inside of the gudeon hole it has a ssection that comes out, this hold the bearing in the same spot as if it was filled in so to speak , but being open it get oil on that side casue its not closed in.  if you pull the gudeon pin out you can see it has this  section it sits on, and the bearing still runs inside that point.    That piston will work fine in that motor dont worry.