I think my motor just blew

<< here are the riding terms >>
- sand,hard pack, dirt track (non organized)
- checked fluids on every trip
- changed oil regularly
- not overlly aggressive on the quad
- rolled only once ( was not even going fast fell off in a deep truck rut )
- cleaned and checked for wear

<< here are the problems >>
- no first gear
- shuts down when shifted into 4 th gear
- metallic clankiong inside the block
- constant rattling inside the block at idle

any help is greatly appreciated. I am expierieced with minor to mild motor mods. So if it get to technical I will have to pay for it. Also I am looking for the cheapest way to go. I figured now would be the time to swap on the aftermarket internals so if someone could help me get in touch with knutz and also scooby I would also appreciate it