Intermittent rod knocking sound.
01-17-2011, 10:30 AM
#1
TECH Regular
Thread Starter
Join Date: Nov 2010
Location: Your GF's pants
Posts: 443
Likes: 0
Received 0 Likes
on
0 Posts
Intermittent rod knocking sound. Hey all,
In my G8, all mods in the sig and no DoD, I have had this noise before and after I did my cam swap. On SOME cold starts there's a weird like rod knocking kind of sound on the passenger side of the engine. But rods don't just go away. On SOME cold starts it doesn't do it at all. I'll drive it to school, kill it, let it sit for a couple hours, and then come out to it and restart it and it sounds like the rods are falling out of it again, then drive it for awhile and it goes away. And I've rapped it to 6500 numerous times and it hasn't split apart or shown any sign that it's going to. The car is nasty fast and has no sign of mechanical failure in the engine. Just this crazy noise. What are the possible things that could be making this motor make noises like that? A rocker shearing apart, or something in the Cats rattling around etc, etc.
In my G8, all mods in the sig and no DoD, I have had this noise before and after I did my cam swap. On SOME cold starts there's a weird like rod knocking kind of sound on the passenger side of the engine. But rods don't just go away. On SOME cold starts it doesn't do it at all. I'll drive it to school, kill it, let it sit for a couple hours, and then come out to it and restart it and it sounds like the rods are falling out of it again, then drive it for awhile and it goes away. And I've rapped it to 6500 numerous times and it hasn't split apart or shown any sign that it's going to. The car is nasty fast and has no sign of mechanical failure in the engine. Just this crazy noise. What are the possible things that could be making this motor make noises like that? A rocker shearing apart, or something in the Cats rattling around etc, etc.
01-17-2011, 09:17 PM
#4
TECH Regular
Thread Starter
Join Date: Nov 2010
Location: Your GF's pants
Posts: 443
Likes: 0
Received 0 Likes
on
0 Posts
I wish that I could agree and let it alone, but it's not Piston Slap, and it doesn't happen only on Cold Starts..... It'll continue making noise after it's up to running temp unless I jump on it and rack it back, then it goes away. This noise just started as soon as I got it back from the dealership because they did some head work as an E3 Spark Plug broke and knocked a hole in an exhaust valve before I supercharged it. I was hoping that perhaps someone would tell me that it may be the broken pieces that I never found rattling around in the Cats, or that maybe it broke the rocker seats on a cylinder, or anything like that. Sorry I didn't include that info on the first post.
01-18-2011, 09:36 PM
#7
TECH Regular
Thread Starter
Join Date: Nov 2010
Location: Your GF's pants
Posts: 443
Likes: 0
Received 0 Likes
on
0 Posts
The reason I did a whole valvetrain swap and LS7 lifters (No DoD) is because I wanted to make this noise go away. I even did brand new heads. New cam gear. Etc. And my oil pressure is outstanding. SO..... I will try to get a video of it, and thanks for all the suggestions but I know for sure that it isn't lifters. 
Trending Topics
Haha like any of them would.
01-19-2011, 06:41 AM
#9
Launching!
Join Date: Oct 2007
Posts: 266
Likes: 0
Received 0 Likes
on
0 Posts
No way in hell that a rod will knock intermittently. It may knock only under load, but it'll do it consistently. If you had rod knock, you wouldn't have good oil pressure and you wouldn't have done many 6500rpm runs.
Have you checked your flexplate for loose bolts or cracks?
Have you checked your flexplate for loose bolts or cracks?
01-19-2011, 09:08 AM
#10
Staging Lane
Join Date: Jul 2006
Location: Texas
Posts: 55
Likes: 0
Received 0 Likes
on
0 Posts
Had something similar, mostly at cold start until warmup, but would occasionally make noise after warmup... couldn't figure it out, took it to a shop, they said it was something in the block, not valvetrain. Turns out it was a camshaft bearing. And by the time I figured it out, it was coming apart and would have needed work done inside the block. Viewed it as a chance to UPGRADE motor....lol. Good luck finding the culprit, hopefully it isn't anything major.
01-19-2011, 06:50 PM
#11
Noise I work for G.M and piston slap 9 out of 10 times is the culprit.We have had people complain,bring the truck in...nothing.One week later it is slapping again.Just my opinion,I hope it is something simple and cheap for you.We have 3"slappers" in our shop right now.It is usually one piston for some reason.Never two or more.Strange but true.
01-19-2011, 10:47 PM
#12
TECH Regular
Thread Starter
Join Date: Nov 2010
Location: Your GF's pants
Posts: 443
Likes: 0
Received 0 Likes
on
0 Posts
Damn damn damn, ok well here's what I can tell you, when I swapped cams, I checked all the cam bearings. Nothing, they looked like brand new. It's not in the block specifically because my knock sensors won't pick anything up. I'm so confused. By the way the sound is more on the top end on the passenger side. No bent pushrods either. Mains don't go away either do they? If I swapped all the top end parts excluding rockers, wouldn't that mean that the rockers, might have an issue? Ugh I know you guys are thinking I'm ignorant for not taking the advice and suggestions here, but this motor absolutely DID NOT have this noise or any trace of it for the past 30,000 miles until the spark plug broke. It broke so bad that the stock cylinder head had to be sent off for patching. So I'm stuck. If I'm just going to have to deal with it I will, but it's embarrassing....
