Sanded motor

I just returned from a dune trip & found sand inside my boys motor on a 88 lt80. I thought he had blown another head gasket but it was 1 of the carb screws that had come loose. Anyway, there is less than 1 hr. on the new piston & rings & I am wondering if I need to pull the motor & split the case to clean it good so that I don't trash the crank. How big a deal is this? Any help would be greatly appreciated.

I usually just wash it out good w/gas.
I would pull the head/jug/piston to do it tho.
Clean it all up and you'll be good to go.

Thanks!