: 03 4.6 Loud engine knock caused by roller rockers



ltmax
09-03-07, 11:35 PM
I started hearing a very loud knocking noise coming from the engine, especially when cold that sounded like a rod bearing or carbon, and the car started missing and was way down on power.

Tried all the usual recommendations for removing carbon etc but nothing worked. When I finally gave in and started tearing the engine down, I discovered three of the four roller rockers were not in place under two cylinders on the exhaust valves on rear bank of the motor.

The rockers weren't damaged and nothing was loose or worn, and as soon as I loosened up the exhaust cam and placed the rockers back in position and put it all back together, the noise was gone and it runs great again.

Has anyone else experienced this problem? I don't understand how these roller rockers could come loose and get spit out from under the camshaft.

eldorado1
09-03-07, 11:50 PM
That would point to a problem with the lash adjusters. Could be a blockage in the oil feed line, preventing them from getting oil pressure. Or even something as simple as bad oil... Don't be surprised if it comes back.

AJxtcman
09-04-07, 08:31 AM
It will be back.
was it #5 or #7?

ltmax
09-04-07, 10:52 AM
I'm not sure how the northstar cylinders are laid out numerically, but it was both roller rockers on the exhaust valve for the third cylinder in counting over from the passenger side, and one roller rocker from the second exhaust valve over.

What do I need to do to make sure this doesn't happen again?

The motor only has 75k on it and no signs of wear on anything and it runs great.

Highline Cady
09-04-07, 01:33 PM
You can fix it by putting in new pistons. That's the GM fix for that. Then it'll knock all the time though.

ltmax
09-04-07, 01:43 PM
Maybe I'm misunderstanding something, I don't understand how roller rockers coming off inside the cylinder heads equates to needing replacement pistons, do you mean the lash adjusters under the overhead cams or do you thing that the pistons are hitting the exhaust valve and causing this?

AJxtcman
09-04-07, 01:44 PM
rear head?

ltmax
09-04-07, 01:49 PM
yes, rear head middle two exhaust valves, both rockers on one and one on the other

ltmax
09-04-07, 01:50 PM
yes, rear head middle two cylinder exhaust valves, both rockers on one cylinder and one of two on the other

AJxtcman
09-04-07, 02:54 PM
We have had just a few with a strange rattle at times. Comes and goes. The last one I had I did a carbon treatment and the engine blew up right after. I had troubles turning the engine over by hand with the plug out before I started it after the carbon treatment. We have a sucker machine and I kept sucking crap out of #7 until it would turn over by hand. Then it poked a hole in (I think) the head. So that got an engine. I think that was #3 for this strange noise.
This brings me up to last Thursday. I have an engine apart currently. I found a similar noise as before. I have no misfires. I think the Exhaust valves on #5 cylinder are hanging form time to time, but I have NO misfires. That would be very odd. If the Exhaust valves hang the followers would fall out. I will keep you posted on my findings.

Highline Cady
09-04-07, 08:13 PM
Honestly I scaned this thread, I also have an 03 that knocks, and was told by the dealer the fix would be new pistons, maybe my knock is different than your knock, but that then it would knock all the time. That's all. Just relaying what I was told, like I said my knock might be diferent than your knock. Good luck either way.

AJxtcman
09-05-07, 07:53 AM
Honestly I scaned this thread, I also have an 03 that knocks, and was told by the dealer the fix would be new pistons, maybe my knock is different than your knock, but that then it would knock all the time. That's all. Just relaying what I was told, like I said my knock might be diferent than your knock. Good luck either way.

This is like that noise from the SLS that I was working on that blew up the day you were over. It was a few months ago. The motor expired in the shop. It had something floating around in it.

ltmax
09-05-07, 08:43 AM
I'm glad I caught mine when I did, there was absolutely zero damage to the top end, I just hope that we can figure out how to prevent this from happening again.

codewize
09-05-07, 09:41 AM
Someone should at least, for education purposes, tell the guy that there are not rocker arms in a 2000+ N*

They're described as cam followers. It's not the same. No pushrods, no lifters.

ltmax
09-05-07, 11:26 AM
Oops, guess I'm showing my age, not quite up to speed on the OHC terminology. Thanks for the info, I added cam followers to the search thread and I'll try to edit the description thread if I can.

AJxtcman
09-05-07, 02:37 PM
Someone should at least, for education purposes, tell the guy that there are not rocker arms in a 2000+ N*

They're described as cam followers. It's not the same. No pushrods, no lifters.

I call them rocker arms all the time, but I Know what they are. If you ask a part guy for a rocker arm they give you a follower. They do rock, so why not allow it?

The valves are actuated by roller finger followers pivoting on a stationary hydraulic lash adjuster per GM.

Highline Cady
09-05-07, 03:23 PM
This is like that noise from the SLS that I was working on that blew up the day you were over. It was a few months ago. The motor expired in the shop. It had something floating around in it.

Oh ya got ya AJ, yep that's a different type of knock.

Glad you caught it early. Happy to hear you don't have any damage. That SLS popped good.

ltmax
09-05-07, 08:39 PM
Thanks for the info and if you ever run across a similar situation or recommended fix please let me know. For now since I've already decarboned the pistons and heads I'm just going to change the oil and keep my fingers crossed that it was a one time fluke. But somehow I doubt it....so if it happens again, I'll pray there is no damage and go ahead and replace the hyd lash adjusters or whatever those things are called on the OHV engine.

codewize
09-05-07, 10:21 PM
I wasn't saying anyone was right or wrong I was just educating. They do work differently and I was trying to enlighten the unknowing. If you have the cutaway pic I bet he'd be interested in that.

codewize
09-05-07, 10:21 PM
No need to change anything man it's all good.


Oops, guess I'm showing my age, not quite up to speed on the OHC terminology. Thanks for the info, I added cam followers to the search thread and I'll try to edit the description thread if I can.

AJxtcman
09-05-07, 11:32 PM
No need to change anything man it's all good.

I am too old. If you get me going on the down pipe I may blow my top. LOL

codewize
09-06-07, 12:17 AM
Dude. I'm older than you are, stop whining and tell me when I can dyno my car again.


I am too old. If you get me going on the down pipe I may blow my top. LOL

Ranger
09-07-07, 06:54 PM
I wasn't saying anyone was right or wrong I was just educating. They do work differently and I was trying to enlighten the unknowing. If you have the cutaway pic I bet he'd be interested in that.
Someone once posted a VERY NICE cut away picture of the roller follower. Might find it with some searching.

JimD
09-07-07, 07:13 PM
Photo credit to JimD.

Display engine credit to GM Cadillac Division.

http://s70.photobucket.com/albums/i101/JimDphotobucket/?action=view&current=DSC00563-2.jpg

ltmax
09-07-07, 07:56 PM
nice picture, anyone else had these come out of place?

Ranger
09-07-07, 08:09 PM
Never heard of it before.

codewize
09-07-07, 10:44 PM
That's the photo I was referring to. Thanks again.


Photo credit to JimD.

Display engine credit to GM Cadillac Division.

http://s70.photobucket.com/albums/i101/JimDphotobucket/?action=view&current=DSC00563-2.jpg