Engine or tranny knock?

[rockbuggy84]

Put a rebuilt engine and tranny in my truck and know I have an odd knocking sound maybe someone could shed some light on. 90' chevy with tbi, used an early style block (2piece rear seal) that was bored 30over and standard pistons. Has stock tbi heads on it with an edelbrock 3702 cam in it. Trans is brand new rebuild and the converter was rebuilt at the same time.

Now where im lost. When started and engine is cold it sounds great, no knock etc. After warming it will begin to hav what sounds to be a minor rod knock or lifter clatter. As soon as you accelerate the noise goes away, while rapid drop off the throttle you get a couple good knocks. The knocks are so erratic, i cant seem to find the same symtoms through weeks of searching the web. You cant hear it crusing down the freeway, but when you come to a stop it will sometimes be there. Some times i get a constant-knock-knock- until throttle is touched, others erratic-knock-ntohing-nothing-nothing-knock-knocknothing.

I have replaced the camshaft and all lifters with new. Checked all 3 converter bolt and was good there. Cant see any cracks in the flexplate but I can only see so far in there. Im now lost

I have been thinking possibly crank movement, tiny crack in flex plate or if possible something in the converter. Any help would be greatly appreciated.

[ceb0217]

Originally Posted by rockbuggy84

Put a rebuilt engine and tranny in my truck and know I have an odd knocking sound maybe someone could shed some light on. 90' chevy with tbi, used an early style block (2piece rear seal) that was bored 30over and standard pistons. Has stock tbi heads on it with an edelbrock 3702 cam in it. Trans is brand new rebuild and the converter was rebuilt at the same time.

Now where im lost. When started and engine is cold it sounds great, no knock etc. After warming it will begin to hav what sounds to be a minor rod knock or lifter clatter. As soon as you accelerate the noise goes away, while rapid drop off the throttle you get a couple good knocks. The knocks are so erratic, i cant seem to find the same symtoms through weeks of searching the web. You cant hear it crusing down the freeway, but when you come to a stop it will sometimes be there. Some times i get a constant-knock-knock- until throttle is touched, others erratic-knock-ntohing-nothing-nothing-knock-knocknothing.

I have replaced the camshaft and all lifters with new. Checked all 3 converter bolt and was good there. Cant see any cracks in the flexplate but I can only see so far in there. Im now lost

I have been thinking possibly crank movement, tiny crack in flex plate or if possible something in the converter. Any help would be greatly appreciated.

um .30 over bore with standard pistons???? did you hook up the knock sensor??

[g-wizz]

standard pistons, so not flat tops? pretty sure that or something similar is what he meant by standard pistons.

so it knocks at idle? have you tried to pinpoint the noise with a stethoscope? you should be able to narrow it down with that.

[Fredduck]

Originally Posted by rockbuggy84

Trans is brand new rebuild and the converter was rebuilt at the same time.

Checked all 3 converter bolt and was good there.

Are the converter bolts tight and not bottomed out on the converter?
This happened to me, with a brand new install. I torqued the converter bolts down and then fired it up.
It sounds like a rod Knock until you input some throttle and then it goes away and then comes back as you back off the throttle.

[rockbuggy84]

Originally Posted by ceb0217

um .30 over bore with standard pistons???? did you hook up the knock sensor??

Standard as in not forged, pop ups etc. It was not built for high compression or hp, just to be reliable. The knock sensor is hooked up and it will not pop a code?

Originally Posted by Fredduck

Are the converter bolts tight and not bottomed out on the converter?
This happened to me, with a brand new install. I torqued the converter bolts down and then fired it up.
It sounds like a rod Knock until you input some throttle and then it goes away and then comes back as you back off the throttle.

I checked that prior to installing tranny, the bolts will thread all the way down into the converter without the flexplate. I just dont get how it comes and goes? I have had cracked flexplates in the past and it was constant until a touch of the throttle. The noisy is sometimes completely gone at idle and others it wont go away.

[Fredduck]

Originally Posted by rockbuggy84

Standard as in not forged, pop ups etc. It was not built for high compression or hp, just to be reliable. The knock sensor is hooked up and it will not pop a code?



I checked that prior to installing tranny, the bolts will thread all the way down into the converter without the flexplate. I just dont get how it comes and goes? I have had cracked flexplates in the past and it was constant until a touch of the throttle. The noisy is sometimes completely gone at idle and others it wont go away.

Try throwing a flat washer under the head of the converter bolts, if it goes away your converter bolts were too long. there might be just enough slack to let the flex plate shimmy. The flexplate holes are larger than the bolt