Isuzu G-series Twin Cam

ok im determined to find this rattle, atm my motor is quiet when cold but as it warms it develops a rattle/tap that raises with engine speed. Now ive checked cam clearances and they are to spec, compression is an even 135 psi across all four, run the motor without the belt to make sure the alternator etc wherent tapping all to no avail. It seems to be deffinately coming from the topend but i cant pinpoint it, i did notice when the tappet cover was off that the dizzy drive gear has a piece missing off one part of the gear.
The motor runs perfectly despite the noise.

Any ideas?

Cheers,
Danny

timing chain?

I'd expect a cam chain noise to be more from the side rather than the top.

The broken dizzy tooth could explain it. Otherwise it's pretty hard to say - buckets, valve seats, crap in chamber (old splug electrode or broken ring though rings probably ok if its 135psi even, though 135psi is low and worthy of as re-ring etc).

An experienced person with a stethoscope (read: screwdriver) might be able to pick it. (I used to be able to, but not the last time I tried...)

turns out its probably just an exhaust leak right under the head. found the manifold flange to be snapped between 3-4, weirdest sounding exhaust leak though as it resonates through the head.