noisey vortec

[Boog]

Hi guys. I have a 97 with 305/auto, 178,000 miles. Well kept truck, uses no oil, no leaks. One day ago it made a loud metal like pop upon first startup but started real quick as normal but a minute or so after that it started making a light hammering noise. Not as hard as a rod knock but not as crisp as a lifter peck either. Oil pressure is normal, temp is normal. No recent work has been done on it. I just took a look under the valve covers and rockers, springs and pushrods are all fine. Using the old screwdriver to the ear method I tried narrowing it's location down but could not. It appears to be in the #2 or 4 cylinders. As I said there is no abnormal vibration or misfires or SES lamp.
The oil is fresh and still clean.
Do the Vortecs have any history of broken roller lifters or pistons,etc? I am wondering now if carbon buildup on the pistontop is the cause. Each cold start it is quiet but within 2 or 3 minutes it begins that noise again.
I welcome any ideas and suggestions any of you might have.
Right now I'm thinking a round of SeaFoam might be in order just in case.

[airdale94]

Might have broken a piston skirt. Some year Vortecs are known for piston knock, but I think it's on cold start then goes away when warm.

[tompotts]

One thing that happened to mine was a worn out timing tensioner and chain. It sounded like lifters ticking but it was a worn timing chain tensioner.

[Kevin45]

Two things you can also check. Pull the belt off and check the belt tensioner and check the alternator. I had an alternator go bad that after it would warm up the bearing was trying to seize. I had a belt tensioner do the same thing. When I would shut the truck off it would come to an abrubt halt with a clunk. After it cooled it would start with no problem. At first I thought I throwed a rod by the way it acted.

Kevin

[Scott68-93-97]

Originally Posted by airdale94

Might have broken a piston skirt. Some year Vortecs are known for piston knock, but I think it's on cold start then goes away when warm.

Vortec trucks dont have piston skirts there skirtless pistons thats what the cold knock is its the piston slapping in the cylinder until it gets warm enough for the piston to expand, all vortecs 305 and 350 are this way not sure about the 454

[Boog]

Well I have more or less babied this thing around for most of a week and over the weekend it seems to have quieted down just a bit. Not nearly as noticeable as it was. I was going back in to readjust the valves next but I think I'll wait now. I am of the idea that it just might be carbon buildup causing this noise. I did put a can of SeaFoam in the tank a while ago. I keep checking the oil and it still looks good. Let's see if the foam does anything to help. I appreciate the ideas fellas.

[ChevLoRay]

Boog, whassup???

I have some piston slap on my 69, but never noticed any on my 96, but it's a V6. Check with Ellis Baker at Judsonia.....he's knowledgeable. Just give him my name (not screen name) when you call him...if he doesn't hang the phone up...No, I don't owe him any money. His son, Doc, may be of help.

[Boog]

Hey Don. How's it goin?
This thing started out all of a sudden last monday morning at first startup. I've babied it for a week now while checking some things and haven't found the cause yet. At first start today it isn't nearly as loud as it was so I am leaning toward carbon buildup. I will give the Foam a few days to do it's thing before I do anything else. Of all the 305 and 350s I've owned I've not had this happen to any of them.
Doc know anything 'bout Chevys? I thought he was a Chrysler Hemi man. LOL

[Scott68-93-97]

The piston slap knock usually only happens for the first few seconds to maybe a minute the truck is running and has to be completely cold and the noise is not loud in fact its barely noticable, and the 4.3 has skirtless to its a modular motor to the 350 same rods pistons valves etc. ( its a 350 with 2 cylinders knocked off)

[Boog]

True. And mine acts just the opposite. It's quiet for the first couple of minutes and then begins to make the noise. You can hear it in the exhaust head pipe by leaning down behind the right front wheel. Still there but not quite as loud. I'm going to blow it out good on the freeway and see if that helps.

Tompots. when did GM start putting timing chain tensioners on the V8's?

[Scott68-93-97]

Definatly might be a carbon knock, I used to run a little water through the carb on older cars to get rid of the carbon but that doesn't work well or easily with the fuel injection plus when you have a cat the carbon can clog it up once it leaves the motor when using water to do it, you said you ran some seafoam through it correct

[Boog]

Yes, I put a can in the last fillup. I plan to put another can in with the next fillup. It hasn't been out on the highway for over a month so I plan to get it out there and run it up there pretty good for some miles and see if it will burn off some of the carbon. It doesn't get very hot running around town.

[get me on the road]

Boog I would suggest, if you think the noise is loud enough, to get the engine warm so it makes the noise your hearing. Then turn the engine off and turn it with a breaker bar to see if you can hear the noise, maybe even pull the plugs and valve covers to see if it makes it easier to locate the sound. With the valve covers off and turning the engine by hand, if you have a good eye you should be able to see if there is anything unusual in the movement of one of the valves. Just something I thought of, let me know if it helps.

[dh81k30]

Boog,

May sound crazy, probably has nothing to do with the problem, but check your starter mount bolts. I had one break and then sounded like your description.

HTH,

[Boog]

Well I never considered that. Thanks, I'll give it a look.

[Hog]

Here is some info on startup knock for the 1996-2003 Vortec 350 and 305 L31 and L30 engines.

http://home.comcast.net/~cliff_scott/99-06-01-003.pdf

It seems that incorrect main bearings were used in some trucks. I dont think this is your problem however. since your noise starts AFTER the truck has started to warmup rather than immediatley upon startup.

peace
Hog

[Scott68-93-97]

Nice find Hog, haven't heard of that being a problem in these trucks but I have heard of it in other GM motors including the 6.5 diesel. The newer motors have a similar knock like this also 5.3, 6.0 I wonder if its a similar problem with the crank knock

[Boog]

Well it's been quite a while now and thought I'd post an update on my truck. Instead of pouring the Seafoam down the intake I elected to pour it into the gas tank instead. One can treats from 8 to 25 gallons so I put one can in about 12 gallons and ran that through then did the same thing again. I feel like a long term cleaning could be better than a flood and flush. I can't say it has cured it but the engine is definately quieter and all I have done is run the Seafoam through it. Still no SES lamp and still runs great. I'll keep my fingers crossed on it. Thanks everyone.

[Tubbed]

The first thing I would do is to run a compression test on all 8 cylinders. If one cylinder is lower on compression than the others, I would check the valves for that cylinder. If comp. is good on all 8 then you can most likely look somewhere else for your problem. Good Luck.