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big problem need help !!! update 9-10-07 finally see last page

scrappyk5

scrappyk5

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On my way to work this morning I was driving my corvette, and it started missing big time. then i get to my work about a mile later and stop, put it in park its idling irratically and and has a intermittin knock inside the motor, like someone is banging sort of like a deiseling knock when you go to shut a motor
off and it makes that noise. its not overheating and it has oil pressure.
its a 1976 with a 350v8/th350. with hei ignition.
anyone have a clue ?
did i jump timing ?
 
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That certainly sounds like it jumped a tooth or two. I wouldn't drive it any further until you can pull the timing cover or valve covers and verify that you haven't beat up the valve train.
 
amazingly it did it as i got to work. i was thinking the timing chain also,
maybe a guide broke and it jumped time plus the knocking could be the chain hitting. i will start tearing apart to see.
 
Never heard of ANY GM actually jump time. They are nylon toothed gears (one anyways) if they strip off, which I HAVE seen, the timing never stays constant long enough to let the engine run. Even if one tooth completely broke off, there are enough other ones that I can't see the chain "slipping", since it rides on almost 180* of the gear. Is it possible?

Is it perhaps something as easy as a fuel pump that broke? Making noise and not pumping fuel well?

Maybe I thought of that because that's almost exactly what happened to me, minus the intermittent knocking noise. Truck ran bad on the way to work, stalled once, started up, drove in fine, then died on the way home for good from the fuel pump.
 
Well i pulled the no.1 plug and check the distributor and it looks like its where its suppose to be.
I pulled both valve covers and all the pieces are move like they are suppose to, nothing bent,broken or out of whack.
The vehicle at idle is ok but not perfect. once you start giving it gas it seems to sputter and miss. the noise is once every 5-10 seconds or so at idle, but when you give it gas the noise gets more but more irratic.
 
Pull the plugs and see if one looks different than the others. If you have a problem inside the cylinder that might show it faster than anything else. Then its compression test and leakage testing time.

Is the engine original, never been apart for anything? Some mid to late 70's 350's had cam lobe problems. If (wild guess) you lost a cam lobe the pieces drop onto the piston shirts and tear lots of stuff up. The easy way to check this is to see if any lifters have gone out of adjustment and gotten very loose. You will have to turn the engine over a half turn to wiggle all the rocker arms.

Hope any of this helps
George
 
smalltruckbigcid said:
Pull the plugs and see if one looks different than the others. If you have a problem inside the cylinder that might show it faster than anything else. Then its compression test and leakage testing time.

Is the engine original, never been apart for anything? Some mid to late 70's 350's had cam lobe problems. If (wild guess) you lost a cam lobe the pieces drop onto the piston shirts and tear lots of stuff up. The easy way to check this is to see if any lifters have gone out of adjustment and gotten very loose. You will have to turn the engine over a half turn to wiggle all the rocker arms.

Hope any of this helps
George
Click to expand...


I have already pulled the valve covers and started the motor and had it running while looking at the rocker arms. everything looks good.
the missing/sputtering gets worse as you give it gas. the noise gets more
irratic as you give it gas.
the knocking sound is definatley something smacking something but its not steady weather you give it gas or not. the motor is originally from a 1975 truck according to the numbers. it had a small tag on the side you usually see on rebuilds.
i am kinda weighing on dyeager 535 on the fuel pump thing. maybe the arm the rod rides on bent or broke or the spring broke. then if so, the car would not get good fuel pressure and the rod that runs up to the cam has paly in it and that is what the knock is. ?
 
Well i am going to start again today. i guess i will first pull all the plugs to see if anything is wrong there. then i will pull the fuel pump and check that out.
anyone else have any ideas ?:confused:
 
You can always run a compression test, in case there is a bent valve or piston has a problem, etc.

Not going to tell you much, but if it's running poorly, and all your ignition and fuel checks out, might be time to check compression, since there is obviously something mechanically wrong.

Make sure your crank pulley is tight. BTDT. :)
 
update !!!!!!


i decided to troubleshoot a little more before i start ripping apart things.

So i started iit up this morning and it cranked right up good idle, but still the intermitten clank/knock. then ofd cousre i give it more gas and its still running smooth but the noise is more and spurratic. THEN! it warms up and it starts missing and sputtering and the clanking/knocking gets more spurratic.
so i let the cool down for about 15 minutes and then i start it up and it is running smooth again. this time i just let it idle to warming it up and BAM it starts running rough again. i did this four times and all have the same results.
so isnt the timing suppose to advance as your engine warms up?
could my distributor be bad or broken at the end and thats whats causing the clanking/knocking ?
COME ON ALL YOU CHEVY GURUS HELP ME WITH AN ANSWER BEFORE I TAKE THINGS APART I DONT HAVE TO :D
 
I'm tring to tell if your description of "Clanking and knocking" is a description of mechanical noise or of an issue with missfire/backfire etc. You could have a bad distributor cap and be getting crossfire/arcing which would cause a clank/miss noise. You could have carb issues, distributor issues etc. Bottom line is this a metal on metal noise like a bad wrist pin or valvetrain issue, or is it a missfire issue? How old is the motor and how many miles? What is the cold/warm idles oil pressure? What is the cold/warm vacume, and is it steady or does it wiggle all over like a burnt valve or timing issue?

And lastly, have you done a compression check?

More info please:thinking:
 
W7NB said:
I'm tring to tell if your description of "Clanking and knocking" is a description of mechanical noise or of an issue with missfire/backfire etc. You could have a bad distributor cap and be getting crossfire/arcing which would cause a clank/miss noise. You could have carb issues, distributor issues etc. Bottom line is this a metal on metal noise like a bad wrist pin or valvetrain issue, or is it a missfire issue? How old is the motor and how many miles? What is the cold/warm idles oil pressure? What is the cold/warm vacume, and is it steady or does it wiggle all over like a burnt valve or timing issue?

And lastly, have you done a compression check?

More info please:thinking:
Click to expand...

i have not done a compression check, i do not have a guage.
the noise is kinka like a hollow sound.
the noise is not steady in any way and is spurratic.
the vehicle runs smooth till seems to get to a certain temperature,
then all of a sudden its starts to sputter the noise doe not get any worse though whether cold or warm , it just picks up as you give it more gas but its still spurratic and intermitten never steady.
the oil pressure is always around 50 psi till warm up then idles at about
21psi.
the engine came from a 1975 chevy truck that someone had stuck in the vette who knows when. i do not have a clue how many miles are on it.
oh, also , while running there is no type of exhaust smoke.
i do not think its a carb issue.
the sound done sound more to the back of the motor than the front.
i have had it running with the valve covers off and all looks good.
hope that helps some.
oh, on your wiggle question once warmed up, it does wiggle.
would it make that noise if it was a burnt valve?


'
 
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Where in VA are you? I have a compression tester. I'm near fredericksburg.

You can also rent them from some autozone/advanced for a $10 deposit. That's if they have one in stock for rent. I find about 1 in 3 of them have them to give out.
 
Just ruling out that it's not the flex plate bolts backing out. They sound like a rock getting tossed around in the engine. I know this doesn't address the misfire though. Could you have condensation in the gas? Have you took off the dist cap and inspected it for cracks- looked at the terminals underneath?
 
i havent had much of a chance to tinker with it the last couple days but tomorrow i plan on digging in to it. I am going to pull each plug to see if anything is bad there. then i will pull the distributor and check that out.
i am trying to check everything everyone has mentioned but its not adding up.
no matter cold or hot, the noise is there. and its always spurratic never steady.
the car starts quick and idles steady till it reaches warm up, then the engine starts shaking and missing. still the noise clanking or knocking is there still intermitten.
the exhaust blows no smoke at all cold or warm.
so i will update tomorrow evening.
thanks everyone
 
If the noise is consistent hot or cold, I would as suggested check the torque converter/bellhousing bolts first off, make sure the flexplate isn't broken while your there. That was a very good suggestion, loose flexplate bolts (or broken flexplate) can make all sorts of noise.
 
that's what i thought of today, ...you guys beat me too it though..haha. that's right where i'd start for sure. i had a truck that 2 of the 3 flexplate bolts backed out...and at idle you could just barley hear it, but under any type of throttle at all, it sounded like all WWIII was goin on under my truck.
 
01maroonz71 said:
that's what i thought of today, ...you guys beat me too it though..haha. that's right where i'd start for sure. i had a truck that 2 of the 3 flexplate bolts backed out...and at idle you could just barley hear it, but under any type of throttle at all, it sounded like all WWIII was goin on under my truck.
Click to expand...

i will check the flex plate and t/c bolts tomorrow also, but i still have the running all crappy when warmed up.
 
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