Knock in engine during start up

I’ve got a 96 Corsica with 118,000 miles and a 3.1 v-6. There is a knock when I first start up and it quits after it gets warmed up. My shade tree mechanic says it’s a rod knocking and I think it’s just a noisy tappet. He wants to tear the pan off and replace the bearings and oil pump. I don’t think it needs it. Any ideas?

What weight oil are you using in the engine?


There’s a big difference between a rod knock and a noisy tappet. Where is the noise coming from? Deep down in the engine or under the valve cover? I’d think a rod knock would be audible more often than just at cold start.

How’s the oil pressure?

Piston slap is another possibility. It can be mistaken as rod knock, and if in fact turns out to be piston slap its something you can ignored if if the noise goes away.

It’s difficult to say as a rock knock and a rattling lifter do not sound alike.
You think one thing and your shade tree mechanic thinks another so you need to get on the same page.

If it’s a rod bearing rap then it should not quieten down after the engine warms up.
Should have added that a bearing knock may quieten down after a few seconds of operation when the oil pressure hits it but should not require 4 or 5 minutes of warmup time.