nismogirl

I bought a 1989 Nissan 240SX about 3 months ago and it was working fine. Now, it is making a weird knocking sound and I don't know exactly what it is. It is a possibility that it is a rod knocking or a valve, in either case it will cost me quite a bit of money to fix it. Does anyone know if there are any other possible problems that it could have? If so, could you please respond. Oh, I have never been on here before so I don't know what everyone knows, it has a KA24E motor.

Thanks for your help,
Nismogirl