I was able to buy a '67 GTO for $75 (back in 1980) because the owner thought it had a bad crank. It made noise similar to what you describe. Guess what it was? Yep, cracked flex plate.
Last time I had a SBC knock ,I found a loose rod cap. I was lucky , got away with only replacing a rod bearing. Jack
A cracked flex plate is generally loudest on the inspection cover, but it still doesn't jump out at you its very subtle. Sort of a "diagnosis by exclusion."
It might have spit out a cam bearing. I don't know how common that is with a SBC, but I know some engines do it.
Well...... replaced the flexplate. My old one looked okay, but I figured what the hell. I have to remove the body to get to the transmission, so having gone that far, I HAD to do something! Button everything up, replaced my plug wires, as one looked bad. Fired it up and........ same fu*king noise! I listened real good and I still can't pin point the source. It seems to come from the top end, then maybe in the middle, but sometimes in the front. It's almost as if I can hear it where ever I want to. What's killing me is, the engine runs and revs great. Good oil pressure. Doesn't miss. It's just that damn HARD KNOCK! So, any ideas? Timing chain slapping? Is that even possible and would the noise be that loud? Guys, I'm at my wits end. I'm hoping the engine isn't dead. Money is VERY tight right now. If it's an engine rebuild, I'll be down for the summer!
You said you checked the fuel pump push rod but how about the return spring in the pump? Did you run it once with the pump off to count it out? Could also be a broken piston skirt.
Broken piston skirt or wristpin bad maybe? But usually pulling the plug wires like you already did will usually tell you something. Lippy
That's what I was thinking. I did that again today and no change. I guess I'll check the timing chain tomorrow as planned. This has really got me scratching my head. ON THE SIDEWALK!
Damn......You've got a tough one there. Sounds like you've tired everything that doesn't require tear down but that might be where this is gonna take you. Sometimes it's easier to just bite the bullet and start pulling stuff apart.I sure that's just what you want to hear at this point.
Timing chain can do that as I had a 283 do the same thing. Pull your dis. cap off and turn your crank till you see your rotor turn, then turn your crank back the other way to see how long it takes to move again. If it is sloppy you should be able to tell. My engine ran great also, after replacing the chain it pinged like crazy until I reset the timing. Also I know off one case where the chain wore a hole in the timing cover. You can also remove your belts to help locate the noise from your engine accs. then start.
I own a really great tool to pin point noise and vibration it costs around a 100 dollars. I had one that I used at a GM dealership that cost a lot more but this little guy is great and works just as well. http://www.tooldesk.com/automotive/STL97170-Engine-Ear-Elite-by-Steelman.aspx Also rent a scope and look into each spark plug hole for carbon buildup that the Seafoam may have not gotten rid of. These two tools save all of the headache and guess work out of locating the source.
Ok, I only read the 1st page but I had a "knock" in a stock 350 in my '77 work truck. Started out as a light tick that slowly worked its way into a "broken piston" bang. was loudest when it was idleing, would quiet up a little around 1500rpm. Turned out a rocker nut had backed off enough to let the rocker it the valve cover. Don't know if that'll help you at all, but my knock didn't sound like it was coming from the top end, sounded like the bottom end was going to come apart, but still had great oil pressure.
No. But I got to thinking about what I had done just before this all started. I had to change out a motor mount on the right side. It had come complete a loose. It was so bad, the motor was tilted a little. So, I installed the new mount and about 3 days later, KLANG.... KNOCK. That's why replacing the flexplate made sense. Also, when I got reaady to bolt the converter to the flexplate, I had almost 3/8" to 1/2" of space. So, I pulled the converter up and bolted it down. Something must have happened when the mount broke. But what? I'm to the point that I'll PAY to know the answer. Maybe make a contest about it. No one should have to go through this.
If it still has the stock GM sprocket on the cam, with the nylon capped teeth, it can knock if two or three (in a row) lost the nylon covering off of them
I know you're goin' nuts. Speakin' of nuts...did you maybe lose a nut when you changed the motor mount? And is there any way it may have found its way into the engine?
I was one that was figuring it was the flex plate. When you said that did not fix it I got to thinking back on a small block Chevy that nearly made me pull my hair out. When I finally found it the baffle in the oil pan had broken loose on one end ( the front I think) it was intermittently hitting the crankshaft. I brazed it back and all was good. Didn't happen to hit the pan on the frame or something when the motor mount broke did you?
Oh boy! I would be thinking seriously about pulling the pan and timing cover off and giving everything a good going over. Check the chain, the rods and mains too. Better to find the noise now before it makes that final BANG and makes a mess on the road.
My friend bought a 86 chevy c10 and it had a clanging noise. We changed and checked everything and the noise wouldent stop. It drove my friend so nuts he started tearing the motor apart and when he pulled the head off there was 13 pennys in the number 6 cylinder! Cleaned the pennys out and no more noise. You would be surprised what things end up in an engine...
I had one like this back in the eighties. The noise was there, but you just could not pinpoint it. I started pulling the engine and I noticed that the pivot pin in the nose of the starter had lost a clip and had backed out. This allowed the starter gear to float a little bit. Damn thing was bouncing off of the ring gear on the flexplate. I was prepared to tear the engine apart and it turned out to be the friggin starter.
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