Crypto can be very profitable, but you should be aware of it's pitfalls.
You itself mentioned already answered and says repetitive answer this op and others dude. That is his problem whether he want to sell the bike for btc or fiat cash. Both would be money according to me btc users. He just asking conversion of bitcoin for the value 4k us dollars just check in Google and explain him that's it.
The best advice I will give to this guy is to find someone physically to sell the motorcycle to and then use the money he got from selling it to buy Bitcoin and fund his wallet.