Bartosz, no doubt you're right. But I am wondering if perhaps your selector arm stopper bearing failed and caused the big mess? This really does seem to be an issue, and should not happen. Especially at your low mileage.

While what you have written is true, I still think that mainly this is a good engine. The selector stopper bearing is obviously something to watch for.

Also, it's possible for anyone to wreck anything. XR400s have a reputation for bullet-proof reliability here in Australia. A friend of mine has >100,000km on his bottom end, another has >60,000km without even a camchain being replaced, yet I have see one fool ruin his engine in about 8000km through brutal abuse. This is not a reflection on you at all, but maybe the previous owner of your bike.

Of course this doesn't help you one bit. I'm just trying put things in perspective. This fed person does understand a hungry one - I had a Ducati dissolve in about 10,000km, and a BMW R100GS which was so bad that the selling dealer wouldn't take it back for any money. Been there, mate, and didn't like it any more than you do now.