Mark,  wish i could figure this picture link out.  

definitely a 2 no question 

I was questioning the 3 vs 8 until i decided the 8 would have equal circles, this one does not, lower circle larger. 

unfortunately, at the 10 oclock position of this 8 / 3 is gone. 

I may have taken it off cleaning the carbon off.  

gotta get this mic set, check the diameter around the skirt, get a bore gauge in the cylinder and hope i dont need to get it bored.   Would be nice if it was in tolerance and a honing is all it needed.  

Thanks for your input.. its valued 

Drac

Have a read of this previous thread.

A few ideas on how to post IMGUR Pictures - Vintage Enduro Discussions

Piston doesn't really tell you much except the general size.

The important thing is the bore size, taper, and out of round... 

The factory bored and honed the cylinders to "spec", say 80mm on a production line. (It would be cost-prohibitive to have a machinist hand size each cylinder to clearance the piston as is done with a rebore.)  The "9" number on a new Yamaha standard piston for these bikes is the size.  A "96" on a piston made for a 80mm nominal bore meant the piston was 79.96mm.  Then it was a simple task to measure the new cylinder and select the correctly sized new piston to get the clearance correct.  (The factory often had more standard sizes than were sold as spares).  So if the new bore size measured at 80.02mm, and the piston is 79.98mm, the clearance is 0.04mm.  If the new bore was exactly 80.00mm, then a 79.96mm piston would be selected if the target clearance is 0.04mm.

Factory new cylinder sizes the piston to the fit bore size.  Oversize bore repair sizes the bore to fit the piston.

If your bore is still in spec, you can often do the same thing by sizing the new piston to get the correct clearance.

On some Yamaha models , not all , standard pistons were offered in a couple of sizes .
Usually .96 and .98 . The variations can sometimes be found , but NOS stock is likely
rare for the larger option after all these years . The size variation was added to the end of the part number ,
a Oceania market RD 400 F piston ( standard oversize ) is 3J7-11631-00-98 .