Droptoplt1ta

* 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?

1NASTYZo6

iTrader: (5)

Based on your conditions. I would think more of Piston Slap than anything. Usually goes away in a few mins to a few secs.

Droptoplt1ta

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.

BAD2000TA

iTrader: (6)

If it was a rod knock, it wouldn't go away. Piston slap is possible, but if it's really loud, probably not.

I'm going to guess that you have a sticking lifter that takes a minute to pump-up.

Droptoplt1ta

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?

BAD2000TA

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?

Droptoplt1ta

148K stock lower end with LS2 chain and Melling oil pump. Oil pressure is great. I used to run the 0W30 GC but that made my engine noiser. I have Penzoil Plat 10w30 in it now.

slt200mph

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...

Droptoplt1ta

Yeah it sounds real bad like it is about to come apart then it is fine. Is there a good oil that can help quiet this down? How about 10w40?

SOMbitch

iTrader: (8)

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...

O2Form

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.

SOMbitch

iTrader: (8)

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.....

O2Form

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.

Droptoplt1ta

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

DaddySS

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.

O2Form

I've had a piece of carbon break off in my 99Ta and it was LOUD but after driving it it slowly went away. Carbon can build up and then break off and make some scary noises. Good Luck

O2Form

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.

Droptoplt1ta

This is louder than a diesel. Could be a piston out of spec..... anything else? Would thicker oil help this loose piston?

O2Form

Something else i just tought of, my 99ta was knocking cold LOUDY once and i tracked it down to the AIR valves. It only knocked cold and it was loud. Check those.

slt200mph

iTrader: (42)

Been running Mobil One 10-40 high mileage oil for the last 100,000 miles ( has 223,000+ now).. it still make the same loud noise for the first minute ... oil will not stop piston slap... when the pistons heat up the noise goes away .. these engines are known for their piston slap ... I always let the engine run for about 5 minutes every moring before hitting the road..the first time I heard it 8 years ago I was worried...but then I found out what it was and have never worried about it since...I have a friend with a 99 T/A that has had this same characteristic and that car now has 175,000 miles on it and runs perfect and has great oil pressure. Like I said it sounds like it is ready for the junk yard on a cold start.

No AIR or EGR or any smog junk on mine .. that stuff is dead weight .. got thrown in the trash long ago.