Loud knock noise that goes away after 1 min cold start
#1
Launching!
Thread Starter
Loud knock noise that goes away after 1 min cold start
* I know this is not piston slap*
My 148k mile 1998 LS1 has a LOUD knock from the lower end that will last anywhere from 20 seconds to 1 minute on a cold start. Then after that the noise completely goes away. The oil pressure is always great
I suspect carbon build up or a rod bearing
Im am pretty sure its not the pushrods
Could be a lifter concern?
I dont think a flexplate since it goes away after the short time
Since the oil pressure is good is a spun rod or main still suspect?
My 148k mile 1998 LS1 has a LOUD knock from the lower end that will last anywhere from 20 seconds to 1 minute on a cold start. Then after that the noise completely goes away. The oil pressure is always great
I suspect carbon build up or a rod bearing
Im am pretty sure its not the pushrods
Could be a lifter concern?
I dont think a flexplate since it goes away after the short time
Since the oil pressure is good is a spun rod or main still suspect?
#2
On The Tree
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Join Date: May 2004
Location: Iowa
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* I know this is not piston slap*
My 148k mile 1998 LS1 has a LOUD knock from the lower end that will last anywhere from 20 seconds to 1 minute on a cold start. Then after that the noise completely goes away. The oil pressure is always great
I suspect carbon build up or a rod bearing
Im am pretty sure its not the pushrods
Could be a lifter concern?
I dont think a flexplate since it goes away after the short time
Since the oil pressure is good is a spun rod or main still suspect?
My 148k mile 1998 LS1 has a LOUD knock from the lower end that will last anywhere from 20 seconds to 1 minute on a cold start. Then after that the noise completely goes away. The oil pressure is always great
I suspect carbon build up or a rod bearing
Im am pretty sure its not the pushrods
Could be a lifter concern?
I dont think a flexplate since it goes away after the short time
Since the oil pressure is good is a spun rod or main still suspect?
#3
Launching!
Thread Starter
It could be, but I dont think it is the typical piston slap that most people complain of. It is VERY LOUD and almost sounds like the engine is about to come apart.
#5
Launching!
Thread Starter
From my experience bleeding lifters typically make a tapping or ticking noise..... This is a LOUD KNOCK
Can the lifters cause a knock on the LS1?
Can the lifters cause a knock on the LS1?
#6
12 Second Club
iTrader: (6)
Well, I guess it all depends on your definition of loud knock. Try posting a video where you hear and then how it disappears. I would think that if you had a bad rod or bearing, that noise wouldn't go away in fact probably get worse. Is the motor stock? Stock pistons, stock rods, stock crank? Any oil pressure issues? What oil are you running?
#7
Launching!
Thread Starter
Well, I guess it all depends on your definition of loud knock. Try posting a video where you hear and then how it disappears. I would think that if you had a bad rod or bearing, that noise wouldn't go away in fact probably get worse. Is the motor stock? Stock pistons, stock rods, stock crank? Any oil pressure issues? What oil are you running?
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#8
TECH Senior Member
iTrader: (42)
Piston slap is the noise sir....I have heard LS1 engines that sould like they have a rod bearing out of them when cold started and low and behold 60-90 seconds later are quiet as a church....I have one with 223,000+ miles on it and it has sounded like that for 8 years...oil pressure is always great and the engine runs perfect...but the first minute after you cold start it you would think that it is junk...
#10
TECH Senior Member
iTrader: (8)
Piston slap is the noise sir....I have heard LS1 engines that sould like they have a rod bearing out of them when cold started and low and behold 60-90 seconds later are quiet as a church....I have one with 223,000+ miles on it and it has sounded like that for 8 years...oil pressure is always great and the engine runs perfect...but the first minute after you cold start it you would think that it is junk...
THIS!!!
Read up on Seafoam and it may help but I have a 210K piston slap motor in my Z-71 and don't think twice about anymore....after 8 years of it...
#11
Thread carefully here.....i don't believe this is piston slap. Make a quick video and post it. Could be so many different things but lifters don't knock and piston slap sounds are not a LOUD knock. It could very well be carbon but if were my engine NOWAY would i put seafoam through it!
Go get some Chevron Techron and run that in the gas, much safer IMO.
Go get some Chevron Techron and run that in the gas, much safer IMO.
#12
TECH Senior Member
iTrader: (8)
Thread carefully here.....i don't believe this is piston slap. Make a quick video and post it. Could be so many different things but lifters don't knock and piston slap sounds are not a LOUD knock. It could very well be carbon but if were my engine NOWAY would i put seafoam through it!Go get some Chevron Techron and run that in the gas, much safer IMO.
Why not??? You ever used Seafoam???
When I first got this truck in 02 I ran it through it twice and it was quiet for 2-3 oil changes each time. Techron won't fix it though that is some fine stuff... It is due to several things but mainly carbon buildup on the piston skirts and loose piston to bore tolerances.....
#13
Misusing seafoam can cause lots of cursing.....and cost lots of money. I personally think the slower decarboning Techron does is much safer. Even after using techron I would change the oil though.
OP if you use seafoam bee dam sure to change oil right after using it.
I use Lucas fuel system treatment in every tank of gas and have ZERO carbon issues, it keeps everything clean.
OP if you use seafoam bee dam sure to change oil right after using it.
I use Lucas fuel system treatment in every tank of gas and have ZERO carbon issues, it keeps everything clean.
#14
Launching!
Thread Starter
Yeah this is not a light slap or light knock.... It is LOUD.... The short block has 148k on it and it has been heads and cam for 12k miles now.
It see's 6800 RPM shifts at times. This winter I was thinking about dropping the oil pan and inspecting and then maybe adding the ARP rod bolts
It see's 6800 RPM shifts at times. This winter I was thinking about dropping the oil pan and inspecting and then maybe adding the ARP rod bolts
#15
TECH Addict
I think it's piston slap. These aluminum blocks can transmit noise in strange ways. Lifters have a distinctive clack to them and piston slap more of a knock. If it goes away completely after 30 to 90 seconds it's a pretty good bet it's piston slap.
#17
Both my LS1 cars have piston slap noise, starts making a light diesel type engine sound after running about 30 seconds then once its completely warmed up it gone. Anything else is NOT piston slap.
Piston slap sounds EXACTLY like a small diesel engine running, If you have a piston actually knocking loud it either broken or WAY out of spec. and piston slap doesn't magicly start after 100k miles.
Piston slap sounds EXACTLY like a small diesel engine running, If you have a piston actually knocking loud it either broken or WAY out of spec. and piston slap doesn't magicly start after 100k miles.
#20
TECH Senior Member
iTrader: (42)
No AIR or EGR or any smog junk on mine .. that stuff is dead weight .. got thrown in the trash long ago.