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3.4 knock

C

cavell

New member
had a few 3.8 cars and just got a 3.4 nox with bad headgaskets and upper knock? its an 06 so it has roller lifters and rockers. cleaned all lifters and all depress properly. inspected all rockers. motor runs cool now but still has knock. so, i have clean lifters, rockers, good pushrods, valve springs all look good. i removed valve covers and all rockers/rods seem ok. all are tight and i can turn/rotate pushrods at tdc. so, whats next? worn piston pins?
 


Is the knock down low? Do you hear it if you do a quick rev when you let off?

If so..that's rod bearings. On the 3.8's we can't just put in bearings and have it last long, not sure if the 3.4 follows the same rules. May be less cost to pick up a used motor.
 
i have not changed lifters or rockers so i cant positively rule them out. i think it is a top end knock/tap that so many 3.4's are known for. i got the suv for $350 so i dont feel bad putting a little more into it. $40 for headgaskets and it runs but knocks. $60 for lifters for giggles?
 
Having done this repair myself, if you are flipping the car, you might even try "rebuilding the lifters" first. There's a few youtube videos on this and this worked well for me. Personally, I'd replace them if I wanted this for my daily driver. If you pull the heads, take a look at the exhaust valves. They're commonly very worn and or pitted. If that's the case, it never hurts to try your hand at valve lapping though if they're pitted badly, I'd go to a shop to have them re-cut. Then I use degreaser and 800 grit scotchbrite pads to prep the gasket surface and use plenty of copper gasket spray on both sides of the gasket. Good luck!
 
motor is assembled and running. i did take lifters apart and cleaned all bits. they all seemed identical. all had nice tight seal where i had to push checkball to collapse them as you would expect. ran suv for 1/2 hr or so. and noise remained. so, i yanked off upper plenum to remove rear valve cover and checked rear cyls at tdc and all rockers are tight and i can rotate/twist pushrods. no slack or wiggle in rockers. i had heads off of course and did not remove any valves. i ran it on sat and took it apart on sun.
 
too make it clear. i bought it running and noisy. tore it down. replaced head gaskets. ran it this past weekend. coolant temp issue seems gone. but noise remains. if i yank motor i might tear it down for fun and inspect bearings.
 


Took off intake. Seems I got 2 pushrods in wrong. 1 is bent. So, I have an issue now. But why was motor noisy BEFORE I messed up the pushrods? It sounded noisy last week and noisy after I fixed it. Is my 1 bent pushrod the issue or is there still another problem?
 
cavell said:
Took off intake. Seems I got 2 pushrods in wrong. 1 is bent. So, I have an issue now. But why was motor noisy BEFORE I messed up the pushrods? It sounded noisy last week and noisy after I fixed it. Is my 1 bent pushrod the issue or is there still another problem?
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Sounds like you could have possibly mixed up the pushrod order from the first repair? I'd inspect the roller lifter surfaces. I usually dissassembly each lifter, spray the crap out of them with solvent, re-assemble, soak overnight in solvent, then let dry and add a few drops of oil and check that they aren't binding. Sometimes (from long oil change intervals) they get thick deposits inside so they "seem" fine by depressing but it isn't until you take them apart that you can really clean and inspect them. Just don't mix any parts between them and make sure you label them accordingly.

Personally, to be on the safe side, I'd go to the junkyard and grab the rockers, lifters, and pushrods from a donor engine and make sure you keep them all together, then clean the lifters and have another go at it. DON'T over-tighten the rockers! Also, it isn't necessary (and not recommended) to soak the lifters after being "rebuilt".

Good luck!
 
Only been 1 repair. Motor had top end tattle/knock. I pulled heads AND cleaned lifters and put it back together. With the 2 pushrods swapped. And I am pretty sure noise was same at day 1 vs today.
I called boneyard and they will sell me lifters/pushrods/rockers assy for $11 each bank or $22 for all. That's 36 parts. Hmmm. And keep them all in order? Whoa.
 
cavell said:
Only been 1 repair. Motor had top end tattle/knock. I pulled heads AND cleaned lifters and put it back together. With the 2 pushrods swapped. And I am pretty sure noise was same at day 1 vs today.
I called boneyard and they will sell me lifters/pushrods/rockers assy for $11 each bank or $22 for all. That's 36 parts. Hmmm. And keep them all in order? Whoa.
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Ah, I see. Lol it's not as bad as it sounds. I usually I bring and old cardboard box, cut slots for the pushrods and rockers, label them as I remove them, wrapping some stiff wire over top the lifters to keep them from moving, and place the whole small box in a larger one to keep them safe and in order. You really don't need to keep the lifters in order, but I usually do just to be safe. On these engines, I make sure to run a thread chase through all the rocker mounts, clean the holes, and apply a bit of lubricant to the threads, then torque to 15 ft lbs if I'm remembering.

If you're talking $22 for all parts, that's a deal. I'd do the above and just carefully take apart the lifters and clean them in solvent overnight. Make sure you lubricate the rocker needle bearings, pushrod contacts, and any wear surfaces. Do not pre- soak the lifters in oil.

If you still have noise after all that, it's probably coming from the block.
 
I figure different used parts might make a difference. Don't see why the order of lifters is important since I am still using my old cam. All lifters will be running on different lobes. Is my issue due to low oil pressure? Motor guts were very dirty. Have not dropped pan to inspect pickup.
 


Yup. With hydraulic rollers, it doesn't really matter. Only reason pushrods and rockers matter is where they wear together. And good luck. The pan is a gaint pita. I'd rather pull the engine before drop another 3.4 pan in the car. If you've got low oil pressure, you got much worse issues to worry about than top end noise. Lol
 
Ran motor till warm to check temp issue. With bent pushrod knocking away. Dang. Stuff happens. VC are off now and there is plenty of oil on top of heads so I have some oil pressure. Put it together and check oil pressure? Or swap out lifters first?
 
cavell said:
Put it together and check oil pressure? Or swap out lifters first?
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I'd definitely swap the pushrods etc out. If you shatter something, then that engine's toast for sure! Sucks though. I know how much of a pita 3.4s are to tear down.
 
i poured some water into intake ports last night. level had not dropped on the port this morning. might go look at boneyard nox's this week. i know how to take off the intakes
 
Was that just to check sealing of intake valve?

Once you get everything back together, it might not be a bad idea to check compression (even though those rear plugs and icm were located by Satan himself) just to be safe (plus it'll pump up the lifters before initial startup, so less chance of noise, just remember to disconnect icm, fuel pump relay, injectors first).

Can't wait to see a video! Haha
 


i knew headgasket job would be a bit of work. i thought the knock sound was maybe lifters and could check them when heads were off. a number were gummed up good so i thought maybe cleaning them would fix noise. parts wear on all motors and 1 car with 140k miles might be quiet while another is noisy. will different lifters and rockers result in same noisy motor? might be some worn wrist pins or rod bearings. i really dont want to put in a remaned motor but a used motor kinda bites too
 
If you want to know where the noise is coming from buy yourself a $3 stethescope from Harbor Freight and listen to the motor while it's running. You can fairly accurately pinpoint noises with one.
 
Has anyone here ever had a broken flex plate? I mentioned the snap sound when I rotate crank forward/back. Is that just normal timing chain slack?
 
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