I just said full rebuild if it is a problem with a shot wrist pin as getting to that would require pulling the engine and the head... you'll already be half way there. You didn't even mention this was already rebuilt. What makes you think this was a well built engine? Have you listened to the noise yourself?
The "common" causes of ticking and knocking in the 7M is bad valve lash (a constant, light ticking which increases with the RPM), injector ticking (sounds a lot like the valve tick) and rod knock. It could be a wrist pin or piston slap, but they're not common. Another thing worth checking is to make sure all of the belt pulleys are securely mounted... a loose harmonic damper makes a lot of racket.
To diagnose it yourself, get a stethoscope and track the sound. If it's bottom end noise, start pulling plug wires to find which cylinder has the problem; top end, listen directly to the injectors and then pull the valve covers and inspect the cam clearances.
If you're unfamiliar with diagnosing these things you should just take it to a mechanic you trust for a solid diagnosis; Especially if this is going to be your only car.
|