split my casing and found this pics added

wots the best thing to do just sand it down a little. and y do u think its happend

 

the image doesn't show enough of the location to know if its somewhere important or not. Stick up a picture of the bigger area

 

Why did you strip the engine down?

It looks as if maybe a piston ring has snapped and some of the fragments have fallen down under the crank which then ground them into the case causing the marks.

Either way its not important...you could sand it if you like but its not like anything will be touching the surface when you put the engine back together.

I'd say ignore and clean the outside of the cases instead!

 

something has let go in the past and this has been striped and rebuilt before, other than the marks the orange instant gasket is a dead giveaway.
i really wouldnt worry about it as long as where the bearings seat is nice and clean you should be ok :good:

 

got to agree...they're not a problem. Remenants from some debris...probably a piece of piston ring dropping into the bottom when the top end has gone bang.

Just make sure all the gasket surfaces are clean and give the casings a good wash out before reassembly :good: