Tapping Noise From Engine

[Keith Ulyatt]

Need help and advice quickly, before I decide whether to pull the engine. Whilst the car was laid up for a month I had the silencer off and modified it internally and changed the oil and filter. Then took it out on the road and got a nasty rattle from the engine at revs over 2500 whilst under light load. If I accelerated or lifted off the gas, rattle immediately disappeared. Although annoying, I assumed it was a loose baffle due to my surgery as I had not heard anything prior to my mod.
Yesterday, spent the afternoon playing at a sprint course, so using high revs and power. Suddenly rattle big time developed - more like a metallic tapping at all revs, but no loss of power or oil pressure, but had car trailored home and set about investigation today.
Engine is a 3.2 Carrera unit in an early car, and I rebuilt it just 7000 miles ago. Started it from cold, only occasional tap for first 2-3 minutes whilst idling, then developed to a constant tap frequency increasing with rpm, but occasionally disappearing for a few seconds. It is very loud, and sounds like a machine gun if the engine is revved. Oil pressure at start (idle) initially 100psi dropping quickly to 30psi as warmed. Noise appears to be coming from front of engine, and more towards the drivers side (RHD). Climbed underneath with a listening stick (screwdriver), but cannot determine exactly where the noise is coming from. Pulled the cam covers on this side - all head nuts appear to be present and rockers/shafts all seem OK. Turned the motor without spark plugs in by hand and on the starter but could not hear anything. Disconnected fan belt to eliminate alternator from equation, but it wasn't that.
Allowed engine to warm up and recorded following oil pressures. Temperature 180 deg.C, idle pressure zero on gauge (needle always has been on bottom mark when hot and idling ever since I installed the engine), 2000 rpm gauge reading 40 psi, 3000rpm gauge reading 75 psi, dare not rev any higher due to noise.
What do you think? Is my bottom end now in need of attention, could it be a timing chain tensioner all advice gratefully accepted.

[nhromyak]

Check compression.

Check valve gaps.

Good luck.

[Kemo]

I had a similar intermittent tapping...that turned to constant tapping which got louder and turned into a clanging. it was a failed tensioner. If you could post a sound byte, that might help with the diagnosis. Good Luck.