I've been searching out a knock for a few weeks now. The motor is a 350TPI, and I had the engine in another Z28 at one time. The motor was perfectly quiet in the previous car.

I pulled it a couple months ago and scrapped the car, and put it in a 91 Z28 5-speed that of course had a 305. The only thing I changed on the short block was to add a new high volume oil pump.

Anyway, I get a knock at startup. When the engine warms, at idle the knock goes away. I hear it at 1100 rpm at about 6 times per second. slowly I increase the revs, knock goes away until about 2500 rpm, where I hear it 8-10 times per second. (hard to count when the rpms go up).

I replaced the lifters, push rods and rocker arms with brand new comp cams stuff. still there.

I put a stethescope on the motor. It's not the bottom end, (I know what that sounds like anyway because I've spun mains in 2 305's). Even with the stethescope poked everyplace I can get it, I am still having trouble finding it.

I'm wondering how fast the oil pump spins in relation to the engine speed. Is it 1/3? Anybody ever had a new oil pump that knocked? Seems unlikely, but I'm running out of ideas.

 

Oil pump runs at Camshaft speed- 1/2 the speed of the crank.

If your oil pump was out of whack to the point you heard a noise it would chew itself up in no time at all.