OK, let's play name that noise ?

I will start with qualifying the project with some info I posted in a previous thread,

I recently took a 1996 LT1 Coupe , started a major tune-up, You know the usual, spark plugs, wires, optispark. When I got in that far I decided what the heck and went ahead with an LT4 Hot Cam kit.
The kit includes cam, springs, caps and keepers and 1.6 roller rockers. I also decided at this time to by a new GMPP lifter kit.

So after taking my time, (several months) got it all back together and it ran great for a few miles. realized the stock pcm WASN'T doing it so I ordered a new PCM programmed for the upgrades. Installed NEW pcm and still ran fine.

Took it out and ran it hard a couple of times, still all was OK.

One day I went out for a leisure drive, nothing hard. Shut off car, came back out an hour later and NOW I had a ticking noise.

Previous thread, I found this to be a bad lifter (new one at that )
Changed it and that ticking/clatter noise went away and solved that particular problem.

NOW, I have a knock.
The car still runs great, idles great and accelerates great.
The Knock IS NOT there at idle.
The Knock IS NOT there when cold.

Once warmed up, The knock occurs around 1500 rpm and up.
Most predominant in the 1500 to 2500 range.

Used a stethoscope and cannot hear anything unusual in the top or bottom end.

Next I started to cancel cylinders by disconnecting injectors.
When I disconnect cyl #8, I now hear the knock at idle. Plug the INJ back in and knock goes away until 1500 rpm or so.

What does everyone think this may be ?

I have had a tough time adjusting the preload on the lifters, they seem right but the rockers still just seem loose to me. Mainly the last one on Cyl #8.

Another bad lifter ?
A bad rocker ?
or worst case , do you think I spun a rod bearing ?

I do not know yet, but want opinions before I make a major decision.

 

I don't think you spun a rod bearing...you hear that all the time...I 've spun a few to many. I'd go back and look at the stuff you just changed out and pay particularly close attention to the rockers and valve stems for the proper or unusual witness marks.

 

Removed spark plugs they look perfect, Removed Rockers and pushrods and I cannot see anything wrong with them other than just seem to be loose when checking their movement side to side. Valve stem top looks ok, I cannot see anything that looks abnormal. I looked at valve springs and do not see any thing wrong, but may pull them off to check anyway.

What is your take on the knock occuring at idle when I disconnect the fuel injector and going away at idle when I re-connect it.

 

I think you need to scan it to see if it is showing up on the KS.Anything loose around the exhaust area banging it?Anything loose around the serpentine belt area?

 

Already did scan and the knock count goes to 20k plus fast. BUT oddly the PCM DOES NOT back off timing.

What could be loose on or around exhaust that would act this way ?

Haven't looked at the serpentine area since noise seemed to come from the back.
But thanks for the heads up I will check into that.

 

It is interesting about the injector, maybe this is the area to look at.
I was amazed at the video clips (sticky posts on this forum) where it actually showed the injector working ok when cold, then failing at operating temp, and at different operating RPM's.
an injector can go south at anytime.
Tom

 

I once moved the location and also changed out a new injector thinking it was a very noisy one, but it sounded like a lifter, and turned out it was a noisy fuel pressure regulator. Tapped like he*l. That was on a '92 LT1 and the P/R sits right over #8 injector.

 

If you think you have an intermitantly failing injector then take a closer look at them or ohm them out. Improper valve lash may also be a concern those lifters use oil to take out that slack in the lash that you mentioned you were not likeing....if the lash is too loose you could get valve train noise from the slop. I only put a 1/4 to 1/2 turn preload on mine....the books will tell you otherwise...but this is me.

You check ed to see that all your plugs were good...how about the plug wires to the plugs..maybe strap a timming gun pickup on each one to see it they are all good.

 

A bad injector or spark plug should throw a mis-fire code on a 96 ODDII.

 

I remember your last thread, I'm going through the same deal. The one thing I have not read about are the valve covers. I have read where the stock LT1 valve covers have drip tabs that need to be removed when going to 1.6 rockers. Perhaps you have already done this, but I just thought I would throw this out there.

Perhaps also you could readjust those rockers. Sometimes new parts need a little retightening after a few miles.

Also don't rule out a leaky exhaust gasket. Do you have headers or stock manifolds?

If your pcm was tuned the timing retard may have been pushed back or eliminated. But if you had spun a bearing the noise be a definite "Oh Sh@t" noise.

 

Well that tells you it is at least transmitting through the block. That is a lot of counts and yes there should be some timing pulled. Might be part of the cause if it isn't. I wonder about the PCM timing.What kind of gas are you using?What injectors do you have in it? I could be wrong ,but loose lifters( a little if that) should not cause knock. Tap yes but knock no.

 

Manifolds are stock. didn't do anything to the valve covers. If you look at these there really is not any material in the way of rockers.

 

The injectors are the original ones that came in the car in 1996. Gas is pump 93 octane ( at least as they advertise )
Sound is definately a knock. No noise at idle unless you unplug the #8 injector. PLug it back in and noise goes away until you raise rpm.

 

So just to be clear you hear the same knock sound at idle if the injector #8 is unplugged? Have you listened to it with a mechanics stehescope to try and localize it to #8 area? It may or may no be able to do that.Have you done a compression check on that side? I am still waiting to hear from others about wether or not lifter issues can cause a knock. Usually a rod issue or detonation issue.

Engines can make many different noises and people will describe them as knocks, pings, rattles or thumps. A true "knock" is caused by rod or main bearings hitting against the crankshaft. The general cause of that is either too much space between the bearing and crankshaft or insufficient oil pressure to maintain the distance between the bearing and crankshaft. Sometimes you can use a heavier grade oil so that the oil doesn't leak out of the bearing space so quickly. If you're currently using 5 W 15, go to a 10 W 30 or maybe even a 15 W 50. If you can't make the noise go away with that, either the bearings are too worn or it's a different problem. If the engine has less than a couple hundred thousand miles, the only reason for bearings to go bad would be inadequate maintenance.

Other problems that can result in noises like that are:

Piston slap. That's when the skirt (lower part) of the piston is slightly worn and is enough smaller than the cylinder that the skirt "pops" from one side to the other as the engine runs. It's more of an annoyance than a real problem, especially since piston slap typically goes away as the engine warms up a little. It typically takes just a few seconds to go away. If it's piston slap don't worry about it until the engine is rebuilt. Piston slap is quite common among many of the GM 350's, especially in engines that go short distances a lot or don't get adequate maintenance.

Fuel "pinging". That's when the fuel ignites too quickly and causes a sound like something rattling around inside the engine when you step on the accellerator. Use a fuel octane booster or change the engine timing.

Hydraulic lifter noises sounds more like a tapping sound and is usually caused by inconsistent oil changes

That's all I can think of

 

Oil pump?

 

If you suspect a bearing on #8 by placing your listening tool on the oil pan in that area you should get a more pronounced sound. I've changed rod bearings by just dropping the oil pan with the engine still in the car.

Be sure to put the car on Jack Stands before you crawl under.

Jake

 

Removing the injector means less load on that connecting rod. Remove the spark plug and see if it does the same thing at idle. I just can't see any connection between removing the load from the cylinder and lifter, or rocker issues. Any valve train issues would be constant.

Pulling the pan only costs you a gasket, but could answer a lot of questions. Takes about 15 mins to do it and about 30 mins to install.

Could be just a worn rod bearing that quiets down when the oil pressure gets high enough. That's why it happens when it warms up, the oil is thinner and the oil pressure is less.

I hope I'm completely incorrect.

 

Tuff96lt1, my name is jeff rinek. I have been working on my son's 1995 lt1 that is in a camaro. I did the same tune up maintainance stuff as you except I did not change cams, rockers, or even go into the valve covers. Basically, changed water pump, pump drive, timing gears and chain (used lt4) new plugs, wires, opt, had radiator cleaned and pumped. Got the car running great, drove it for about a month. Then after I drove it, and got on it a little bit, the same type of noise that you are describing started happening. It has gotten worse. Originally heard the noise only over 2500rpm then it started moving down and evolved into a full blown knocking sound. I think the area of the sound is within the throttle body. I don't know what could be in there. I can't rule anything out. I am pretty concerned that it is major damage, but as you, the engine runs fine, idles fine, and most importantly there are no codes being thrown. Have you had any luck fixing your issue. Our bang definitely is associated with one cylinder, but when I listen closely it sounds as if it is coming from the throttle body. I put my hand on the throttle body and could feel the bang, and we can feel it in the gas pedal. Any ideas?

 

Sorry Jeff and to all else. Thought I posted the final problem.

After further investigation and research turns out the LT1 has an inherit problem with rod bearings. Evidently the tolerances are a little off from what performance builders use.

In the end I have spun a rod bearing. Some have told me I didn't prime the oil pump before I finished build. Other have said the sitting for 9 months and than a poor prime.
Hard to say which is the real cause, bottom line I spun a rod bearing and am now looking at replacing the engine. Sure I could take it out , rebuild bottom end or rebuild all. But I will probably go with a crate motor and move on. I have looked at Golen Engines as well as Lingenfelter. Too busy now so I have put the project off for a few months.

 

When I spun a bearing on another car, the knock didn't show up till it warmed up and the clearances opened up.

LTX rod bolts are weak. If you overrev it a all, you spin them.