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#633646 - 07/11/05 10:10 PM Telling the Difference between Rod Knock and Lifter Noise
Jim 5 Offline


Registered: 05/25/05
Posts: 4009
Loc: Calgary Canada
When I start my '98 chev k1500 with the vortech 350 I hear a ticking/knocking sound when I drive away cold for the first block or so I travel in my neighborhood. This goes away after shortly thereafter.

My truck suffered the typical intake manifold leak which was fixed about 40k miles ago. At that time, the service manager told me to listen for "rod knock".

The truck now has 170k miles on it.

How do I tell if this is lifter noise vs. Rod knock?

Can anybody give me some advice?

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#633647 - 07/11/05 10:15 PM Re: Telling the Difference between Rod Knock and Lifter Noise
Quest Offline


Registered: 12/19/04
Posts: 7355
Loc: beaver land EH?
sounds like piston slap to me, not lifter noise/rod knock

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#633648 - 07/11/05 10:15 PM Re: Telling the Difference between Rod Knock and Lifter Noise
Drew99GT Offline


Registered: 10/11/02
Posts: 21520
Loc: Colorado Springs
Sounds identical to my Dad's 4.3L Blazer with 180K that, yup, had a leaky intake manfold gasket [Mad] Lifter noise is more a tick tick tick, where as rod knock is more a heavier clacking/knocking sound. The rythem of rod knock will usually be twice as fast as lifter tick as the camshaft is turning half the speed of the crank. My Dad's does it only on cold starts in the fall through winter. And his is definetally not a lifter! I've been told that it could be a crankshaft thrust bearing. Most people say that rod knock won't go away after the engine warms but I dunno.

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#633649 - 07/11/05 10:16 PM Re: Telling the Difference between Rod Knock and Lifter Noise
Drew99GT Offline


Registered: 10/11/02
Posts: 21520
Loc: Colorado Springs
Piston slap is more a clacking sound, not a solid knock. When it's making the noise, does it get louder when you give it a bit of throttle?

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#633650 - 07/11/05 10:41 PM Re: Telling the Difference between Rod Knock and Lifter Noise
Jim 5 Offline


Registered: 05/25/05
Posts: 4009
Loc: Calgary Canada
It gets louder when you give it a little throttle. You can't hear it if the motor is just idling.

It goes away after a block of driving every time. It goes away faster if the truck warms up a little before I drive away.

The 350 vortech's aren't known for piston slap like the 99 and up 5.3L vortechs.

Crankshaft thrust bearings typically fail in standard transmission applications due to pressure from clutch engage disengage. This truck is an auto.

I would call this a ticking sound bordering on a clatter, but not sounding as deep or loud as a knock (It's pretty hard to describe a noise).

Anyhow, I'm running an ARX treatment (halfway through clean phase) and am hoping if it is a lifter, it could be unstuck by the ARX. I'm smelling coolant again and it looks like it's about time to R&R the intake manifold gaskets. This time I'd do it myself, and with the Intake manifold off, it's not much more work to remove the rockers, pull out the pushrods and replace the lifters.

On the other hand, if it's a rod bearing, the repair sounds like a real pain, and I'd be more inclined to try and get my hands on a low mileage vortech 350 (and change out that intake manifold gasket)from a wrecked pickup.

Please keep the comments coming...I appreciate the advice!

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#633651 - 07/11/05 10:48 PM Re: Telling the Difference between Rod Knock and Lifter Noise
427Z06 Offline


Registered: 12/06/03
Posts: 7409
Loc: Austin, TX
A UOA might help determine which it is. High copper/lead = bearing. High iron = lifter.

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#633652 - 07/12/05 01:01 AM Re: Telling the Difference between Rod Knock and Lifter Noise
Jim 5 Offline


Registered: 05/25/05
Posts: 4009
Loc: Calgary Canada
good point 427z06.

I would have thought that should have been my first thought having spent some time in BITOG!

I'm running M1 5w30, which I understand generates higher iron numbers. I guess the tip-off would be a high copper/lead number.

Would a loose con-rod bearing eventually stop wearing because it's loose, or would it continue to wear faster because of the additional slop between the con-rod and the crank shaft?

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#633653 - 07/12/05 01:48 AM Re: Telling the Difference between Rod Knock and Lifter Noise
Ironduke4 Offline


Registered: 05/07/04
Posts: 182
Loc: Chicagoland illinois
A piston slap is caused by excessive clearence between the piston and cylinder and that causes the piston to rattle in the cylinder and sounds kinda like a diesel engine when the engine is cold but the sound gets quieter or goes away as it warms up.
A rod knock will be heard down low in the block and the clacking noise will speed up as the engine is reved up and will usually get louder as the engine warms up and the oil thins out.
A lifter or rocker arm noise will be heard up higher and will usually sound like it is coming from under the valve cover.
A loose rod bearing will wear faster because of the pounding the rod journal gets when that cylinder fires.
This will eventually result in the connecting rod being kicked out the side of the block (thrown rod).

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#633654 - 07/12/05 02:01 AM Re: Telling the Difference between Rod Knock and Lifter Noise
HerkyJim Offline


Registered: 08/11/04
Posts: 189
Loc: The cool green NW
disable ignition to cylinders one at a time. If your knock/tick goes away that's your rod culprit. But a tick is more likely a lifter or exhaust leak or something else. if it goes away its most likely an exhaust leak or lifter. My MOPAR 318 does this sometimes...lifter noise that goes away after warms up a bit or I can usually stop it right away by simply shutting engine down and restarting it

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#633655 - 07/12/05 05:50 AM Re: Telling the Difference between Rod Knock and Lifter Noise
1sttruck Offline


Registered: 03/20/04
Posts: 4378
Loc: Camas, WA
VWs use to 'throw rods' often, due to running hot from being air cooled, a small sump, no filter, and typical neglect. When one was starting to go you'd hear a 'tick tick' that as others mentioned increased with rpm, it'd get louder as it got hot, and would be most noticeable when letting off the throttle after putting a load on it. It would get worse with time, evntually making a 'Whack Whack Whack' at low speed. I've seen blue rod caps and badly chewed crank journals. Really bad rods make a 'KAWAANG SCREECH CLUNK CLUNK CLUNK' noise, and then it gets stays quiet :^)

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#633656 - 07/12/05 06:21 AM Re: Telling the Difference between Rod Knock and Lifter Noise
Chris142 Offline


Registered: 06/05/03
Posts: 13975
Loc: apple valley, ca
quote:
Originally posted by Quest:
sounds like piston slap to me, not lifter noise/rod knock

how bout a wrist pin?

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#633657 - 07/13/05 03:49 AM Re: Telling the Difference between Rod Knock and Lifter Noise
michael harris Offline


Registered: 07/02/05
Posts: 79
Loc: nampa, idaho
overthinking.......
lifters / valves by 70-80% i'd bet. do ya park flat, slight uphill or slight downhill. ?? if ya park nose up try backing it in and be nose down and see if that helps or vice versa..
44H

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