Just did a rebuild on a Gen VI 454. Engine has about 10 hrs on it. Runs fine up to about 1900-2200 RPMs or so.

New mains, rod bearings, rings, and heads redone.

Oil pressure good (40 to 60)
Temp is about 165/170
Not burning oil

The problem is I get a metal rapping/clanging anything above 2200 -2300 especially on hard acceleration and decceleration. It is not a low tump like mains or pinging sound.

Looking for ideas before I tear it down.

Thanks,

Rick

I had a noise somewhat like that within the first 5 hours. I thought I broke a rocker arm stud or valve spring. Turns out the lower crank pulley had worked itself loose and was rattling around. Double check your pulleys. Jeff Wurl

I am with J look for simple first....

make sure the balancer is tight...if you replaced the timing chain(they have 3) and you used the wrong one and/or did not put reluctor wheel back on the balancer will bottom out and wobble out...GM did it on mine new engine...

I agree with all of the above. Also make sure you dont have something else loose in the bilge that could be rattling under those conditions. I thought I had a rocker going out, had a rattle at 2200 or so. After some digging I found a loose bracket, it's amazing how much it sounded like and engine issue.

Time it.. is it consistent? Once per rev?

Timing was set (grounded out T/bolt ignition). still good. Will check h/balancer. Sounds like coming from port side upper.

Will update when I rip into it.

Thanks....

I had some noise on mine after about 10hrs. Turned out to be fly wheel. I must have forgotten to torque the bolts.

same issue with mine exact same, i didnt do the rebuild a marine mechanic did, and after removing heads he discovered a sprine keepers had gotten down in block some how. i guess i was lucky as soon as the soon started i mean the first hint of a sound i killed it.

spring keeper not sprine keeper lol sorry about that