1993 Chevy Blazer Full Size 5.7L V8 knocking lifter

After an accidental redline, while truck was in Park, a lifter became damaged, and my truck starting knocking.  There are limited parts that can cause knocking, and one can usually identify by the location and tone of the knocking, where it is coming from.  While it was easy to identify that if was a lifter, it is difficult to identify which one without disassembling.   Best practice is replace all of them, while you;re already under the intake manifold.

A hydraulic lifer, typically found on gasoline engines, sits in a shallow pool of oil, and is essentially a mini pump.  In the case of a GM 5.7L V8.  The lifter sits atop the camshaft, and due to the camshafts shape, it’s rotation causes the lifters to move up and down at specific intervals as the camshaft rotates.

Right over the lifter sits the push rod which serves two functions.  It pushed the rocker arm, and also allows the lifter to pump oil into the upper valve heads.  The lifter has a piston inside, and spring, as well as a hold on the bottom end, and a hole on the top end:






The push rod is hollow and allows oil to squirt up through it.  In essence:

The camshaft pushes the lifter up
The lifter pushes the push rod up, while sending a oil through the rod
The rod pushes one side of the rocker arm up as well as dispersing oil
The rocker arm pivots and pushes down on the valve which allows fuel in or exhaust out depending on the valve.

Here’s a short on what my engine sounded like with a failed lifter:



So after hearing the noise, I was all like, “time to identify where it’s coming from”.  The best tool for this is the stethoscope:


By the sound being louder when checking the engine block, versus anything else moving around the engine, one can infer that the problem is within the engine block.   Eliminating any issues caused by the pulleys, belts, or anything being rotated by the engine crank.  The next step is to figure out if the noise if closer to the top or bottom of the engine, this can be done by listening to the engine block, then valve covers, then oil pan.

In this instance, the location and frequency of the sound, identified the problem as one of the lifters.  Usually the lifter’s spring will fail, or the bottom will fail, creating enough slack that camshaft “knocks” the lifter into the push rod.


The lifters on the 5.7L are located beneath the intake manifold.  So the valve covers, intake manifold, distributor, and heads must be removed to access the lifters.  This is a good time to check for other problems and refurbish the heads.  This is basically known as an upper engine rebuild.  The engine does not have to be removed.  I didn’t do it, but I probably should have.  Here are some pics for reference.    Please note that for the distributor pic the engine is in TDC (top dead center).  This means that the number 1 piston is all the way up and in firing position.  Also, when removing the distributor, it is normal to see it rotate a good 45 degrees counterclockwise on it’s way up.  The same must be reversed when it is installed.  This is due to the fact that the gear at the end of the distributor is a helical gear.

Comments are closed.