knocking

[neal90]

got a AMC 258 i6 / 4.2l with about 160k on it. The motor runs STRONG. But it knocks when cold... some times the knocking doesn't start for the first 5-10 seconds its running and some times it won't start knocking for 20-30 seconds. And it lasts 3-5 min and than it sounds like a new motor. Is this just piston slap and if so how long can the motor last like this thanks for the help

 

[IrishCJ6]

What's the oil pressure like? Usually when they start knocking the oil pressure drops. Maybe do a compression test as well to see what the engine's like.

 

[neal90]

the oil pressure is rock solid around 30 psi when cold than 15-20 when hot

 

[IrishCJ6]

At idle? or what RPM? Mine is around 75psi cold at 1200 rpm and then around 30 psi hot +/-5psi. At 2000 rpm hot im at 45psi

 

[73CJ]

A deep knock or clicking?

Deep knock usually a rod bearing.

Clicking is usually normal from used AMC 258 i6 / 4.2l tappets.

Cold mine hits 60 psi on the rebuilt motor. All new bearing and pistons.

20-25 hot.

Compression test will tell you about the pistons and rings. Burning much oil?

If your oil pressure suddenly goes to 0, you've spun a bearing. Pull over and save the bottom end from more damage.

I never heard a knock, but spun a crank bearing. Not too hard to drop the pan and check the clearance with PlastiGage. You're gonna have wear depending on how often the PO changed the oil. . .

 

[neal90]

All the psi are at idle speeds Andy carb is missing the part the controls the high idle at a cold start so it always idles real strong at
Around 700 rpm and its just a loud clicking sound from the
Front top of the motor

 

[IrishCJ6]

It's not just a noisy hydraulic lifter? or a noisy tapet?