Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Lifter tapping or rod knock

Okay hey guys I’ve made a post about this before but old account wouldn’t let me login so had to make a new one, anyhow I’ve have this knock or tap in my engine that I’ve been trying to figure out for the longest time, it started about a year ago & could barely hear it at all I would have to point it out to my friend because it was so quiet but gradually got louder over time it’s a consistent tap, not clunky or off rhythm ,///when I first start the car on cold start it takes 1-2 mins for it to start tapping then if I turn off & restart the car than it starts tapping immediately, I’ve changed these parts -
This is a 3.400 v6
Knock sensor
Oil pump
I thought it might have been a collapsed hydraulic lifter so I took them apart & cleaned them, I don’t know if that would help a collapsed lifter or not.
Ive also replaces a few other odds and ends
time serts for all rocker arms
All new gaskets from the heads up
I’ve checked the block & everywhere else for cracks all good there flex plate is good it isn’t an exhaust leak, rod bearings seem to have a lil walk side to side to them but for the most part I think they might be okay. The knock or tap seems to get louder From the center, if I run the engine & take each spark plug off one at a time it still sounds the same, but I’m posting a link it’ll take you strait to my engine tapping & you guys can tell me what you think [ ]
That’s idle at running temp & I believe the tapping kinda sounds like it’s tapping half the speed of the crank so that would make it cam related right? Like maybe a collapsed lifter?
Also you can see im running it without the belt on so you can eliminate pulleys,this is also a picture of one of the rod bearings they all looked about like this, no pits or grooves it was really smooth, doesn’t look like it in the pic but they all were, none of theses marks would catch my fingernail

Your feeling about the “half pace cadence” of the sound you are hearing would indeed trigger my brain toward the valvetrain / cam area of things… very logical and valid feeling +1 to that. That is indeed a valid characteristic to notice…

I may be making this up but i believe i read somewhere about the Hokie-ness of some new valve rockers and or push rods slipping out there into the new parts supply

I swear i read it in Hemmings… now i need to go find that edition number but the jist of the story was that there are incorrectly tempered and or cheap metal used in the mfg of a large number of new rockers and pushrods out there in the world…

At any rate this is at least possible and common enuf for the editor mechanic at large to recall this and put it in print in response to a fellow scratching his head in the same way you are regarding new parts and yet still having same prob type o thing…

I have to look into this now… either find that Hemmings issue and or search the net to verify that story

I’ll have to check it out in my opinion they should timeserts each rocker thread In the factory

Indeed… its a shame that we can always have the vehicle in front of us, because that is the only real way to diagnose and repair these types of things.

Another item that can absolutely cause you to hear funny noises etc is the lifters… i thought they were on the replaced list… if not… they should be suspected or one or two of them anyway… when hydro lifters cannot maintin that cushion of oil internally… they essentially collapse in use… opening tolerances and inviting a tap. If u are sure the bolts holding down the rockers are ok… id be looking very hard at the lifters

Lifter collapse will manifest precisely as you described above.

Why did i think u replaced them already? I dunno… if not… they are a very “solid” suspect… eventho they are hydraulic… sorry i couldnt resist…

In another life, when i dealt with lifters much more often… if a lifter were to fail… or fail to “pump up” it would usually be one of the front lifters as they get the lesser of the oil bath and they also are the ones to dry out after long periods of time not running… so the ones that die are usually up in the front of the engine near the crank nose.

There is a way to remove your valve covers and run the engine… you need the oil redirect clips on top of the rockers to do this… but u may find a collapsed lifter thata way… need those clips tho to deflect the oil

1 Like

No knock when cold. Oil viscosity? More like metal parts expanding when hot? New rod bearings help? You hope the bearings have worn vs the crank. But, who knows.

The tapping sound doesn’t come off as a rod knock tho rod knock can be consistent to an extent but most I’ve heard were kinda clunky sounding the tapping noise that’s going on with my engine is way too consistent of a tap to be a rod knock plus it isn’t as fast as a rod knock should be