How did sand get into the sump?

Hi,

I was out riding my friend's CRF450 (2003) :ride: through the desert and after bogging down a little in a dune (not by much, just enough to get down to the rear axel) and so I tear off again and no more than 1 minute later it's miss firing.

We take the bike to the shop and they say there is sand in the sump and it got up to the cams and messed with the timing. How did that happen? Is it possible for the sand to get to the sump so easily on a four stroker?

I'm on a bit of a guilt trip as I feel like maybe I was at fault, but my mate reckons it must have been poor servicing in the past.

Appreciate any feedback

OK, I'm not too hot on the mechanics, but I can see some small amount getting past the rings. But how does a four stroke engine let it go round via the exhaust? (aren't exhaust ports exclusive to the 2 stroke?),Seriously, I'm not that smart so any further expanation is good for me, Thanks for the post