Cold engine knocks at idle *movie*

[Johny Bee O]

Hi all

When my engine is cold i hear a metal knocking and it goes away when its complete warm. But after a short shut down, its knocks also when its warm but not so loud as is cold.
Im guess it can be the lifters but im not sure... i have this problem since 40kmiles and now i want to fix it. I removed the valve covers and take a short video. How i can test the lifters? Its hard to put a screwdiver between the valvesprings and the rocker. The frequenz of the knocking is slow, so i guess it must be the vavle train and not a rod knock. With more rpms the knocking will be quieter and after 2000 rpms i cant hear it.



Any suggestion or advices what i can do?

[SMWS6TA]

It sounds a lot like piston slap.

[Johny Bee O]

Thank for you advice scott. I checked some piston slap movies on youtube and it sounds very similar but also a bad valve train ( bent pushrod) sounds very similar... I live in europe and a engine rebuilt is expensive so i think its better choice get another engine. But first i would like get more information about the klacking sound, where its comming etc. After i removed the valve covers the sound is different as with the covers...
I used a screw driver and pushed the valves down between the rockerarm to check the lifter but i cant push it far in so i tried this on all rockerarms. After that i start engine and the sounds was gone and come back few seconds later so theres a chance the problem is there, but im not sure...

[SMWS6TA]

I say piston slap because you stated this

When my engine is cold i hear a metal knocking and it goes away when its complete warm and this - With more rpms the knocking will be quieter and after 2000 rpms i cant hear it.

Classic piston slap.

It could be bad rockers but I doubt that, the more you rev the faster and louder it would get if rocker's were an issue.


I've been reading that some guys have been installing a better oil pump and swapping out the lifters (using LS7's) and getting some positive results.

[Johny Bee O]

Update:
Engine cold, i started it and use a stethoscope and listen at the oilpan and there was no knocking or ticking so i hold it on the rockers and there was much louder. After that i used only the tube of the stethosope for better local dececting, and push it in the dipstick tubeline and there was also nothing from the knocking. Next spot was in the near of the pushrod holes in the head and there was a loud knocking, what i think about it ?

PS: My engine use 0w40 and or 5w30 and it consume very less oil and at start up it doesn't smoke after start...

[SMWS6TA]

Well you have a couple of things to do.

Take off the rockers and inspect them (do one at a time and put back in the same place you removed them from) Look at the trunnion bearings make sure none are missing or stuck. They should move freely.

Next pull the push rods out and roll them on a mirror or flat glass. This will let you know if one is bent. If ok reinstall.

Now tighten the rockers back to 22 ft lbs while the cylinder is TDC. You'll have to turn the motor over to get each one TDC.

After you have them all tighten down run the car again.

If you still have the noise then I would say that a stuck lifter is the next candidate.


Now the bad news. If the above doesn't work then you'll need to pull the heads to check for a bad lifter or bent valve.

Once you get the head off and pull the lifters the roller should be smooth and roll freely. The top where the push rod sits should depress slightly when you press a push rod on it. It it doesn't then it's bad.


To check for a bad valve, unless it is so obvious, then a shop will need to look at it.






For the record you have all the signs of piston slap IMHO.

[Firebirdjones]

I agree, sounds like a classic case of piston slap. Very common among the LS1's unfortunately. It's nothing too terrible to worry about. However pistons rocking in the bore, however mild it may be, affects the rings ability to control compression and oil. So some oil usage (blowby) is usually a result. Not necessarily seen as smoke, but low oil on the dipstick between change intervals would be considered mild. Over time it may get worse, but will likely go 10's of thousands of miles before something needs to be done.

The only real cure is an overbore and new pistons. The problem with the LS1's are their lacking ability to be bored much at all. .010 over is about the limit, but with piston slap part of the equation it's likely the bores will be egg shaped to the point that a .010 overbore won't clean it up, rendering the block useless unless you want to go through the expensive resleeve process. Short answer, start with a new block.

[pajeff02]

Agree with everything posted above. Certainly will not hurt to look into it a bit more though to rule out the things that Scott mentioned. What kind of oil pressure do you have on cold startup?

[Johny Bee O]

My oil pressure is good, its on the strip between the 60 and 120 psi mark. After warm up it drops a little but not much... How it can be a piston slap, when i hear with a stetheoscope close nothing on the bottom of the engine?
With a open oil filler cap, its sucks air into the vavle cover, so i guess the crankcase has not pressure from blow by gases. When i pull the heads, its there a area there will be more polish or something else from the piston slap?
And i have this since 40kmiles... so the piston slap should leave traces?

[Firebirdjones]

In a severe case of piston slap you may see scuffing on the skirts and lower cylinder walls. I've seen some that break the skirt clean off and find it laying in the oil pan.
LS engines don't have that much of a piston skirt so you probably won't find much visual evidence of it.

[Johny Bee O]

thats a bad situation. I hear it and i cant see it on the walls so if i pull the head its superfluous? When the engine revs down from 2000 rpm to 1000 rpm the noise is gone... hmm i still hope it would be a vavletrain problem...

[Firebirdjones]

You wouldn't find it pulling the heads. It's a lower cylinder wall issue so bottom end disassembly is required. To really know if there is access cylinder wall clearance would require a bore gauge and calipers. At that point you're in deep and may find yourself rebuilding.
That's why I mentioned if it's not that bad, and goes away when it warms up (classic piston slap characteristic) and if it's not using much oil or affecting performance at all, I'd let it ride.

This was fairly common in the 60's performance engines that used forged pistons, and even sometimes after a rebuild with older forged piston designs. They required as much as .004 or .006 skirt/sidewall clearance, so they usually made some noise when cold, once warm things were fine. Forged pistons have a different expansion rate requiring the large clearance.
With cast or hypereutectic pistons they run a much tighter clearance like .002 for instance. You get quiet cold operation which is why the OE manufactures went this route even in modern performance engines today. So you wouldn't expect piston slap and frankly you shouldn't be hearing it at all. But these LS engines still have it, seems hit and miss. I believe in the 90's there was even a recall for it, for a while.

If you're lucky you'll find something in the valve train, that's an easy fix.

[Johny Bee O]

Crap thats a bad situation... i guess i have tree option now.

1. Do nothing until there is come big problem...
2. Get new heads,cam, vavletrain,injectors,timing chain, oil pump so the complete top is new of the engine still the intake throttle body... and than i hope the knock is gone.. cost $3500- $3800 450-480 hp
3. Get a rebuilded engine as a long block with the same power output. So any suggetion where i should buy it? ebay click link <-- vs. texas speed is 2000$ - 3000$ so a used engine is also welcome...

[Firebirdjones]

Hard to make a decision without being there. In the end what you are willing to spend and the amount of work you want to tackle will dictate how you want to approach it.

Seems to me tossing $3,000+ to rebuild the top end only to see if the noise goes away is somewhat wastefull. Is it really that bad to worry that much about it? None of us can diagnose for sure over the computer.

My best guess is classic LS engine piston slap if it goes away when the engine warms up, in which case as I mentioned, if oil consumption isn't excessive, no codes, no loss of power, and you take care of the car with regular oil changes etc....I'd let it ride. People run these things for years like that.
If it makes you feel better I'd send a sample of the oil to Blackstone for an oil anylis and see if it comes back with any unusual results that might suggest excessive engine wear. If it's fine, don't worry about it.

If you really want a new engine, I'd probably look into Texas Speed or one of the other many LS suppliers and do some price shopping. I tend to lean towards a cast iron 6.0 build to get away from the LS1 engine idiosyncrasies.

[Loser]

I have the same issue with my 2001 WS6. I ended up pulling the heads and changing to LS7 lifters but that did not resolve the issue. I also changed to slightly shorter push rods after I measured them with the LS7 lifters in place. This reduced the noise level by about 20 or 30% but did not eliminate the issue. I have had the problem for over 60,000 miles on this motor which has 195,000 miles on it now. There are a couple threads on here from when I was trying to resolve the issue.

- Tom