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Knock... clang...WTF!

Discussion in 'The Hokey Ass Message Board' started by tfeverfred, Jun 14, 2012.

  1. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    VoodooTwin
    Member
    from Noo Yawk

    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.
     
  2. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    Converter bolts were tight.
     
  3. spooler41
    Joined: Feb 25, 2007
    Posts: 1,099

    spooler41
    Member

    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
     
  4. 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."
     
  5. S_Mazza
    Joined: Apr 27, 2011
    Posts: 363

    S_Mazza
    Member

    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.
     
  6. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    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!:mad::confused: 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.:confused: It's almost as if I can hear it where ever I want to.:confused:

    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!:eek::mad:
     
    Last edited: Jun 21, 2012
  7. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,385

    landseaandair
    Member
    from phoenix

    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.
     
  8. flatheadpete
    Joined: Oct 29, 2003
    Posts: 9,510

    flatheadpete
    Member
    from Burton, MI

    Geez Fred. This sucks! Hope ya get it fingered out soon.
     
  9. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    Yea, I removed the pump totally. Ran it... noise.
     
  10. lippy
    Joined: Sep 27, 2006
    Posts: 4,206

    lippy
    Member
    from Ks

    Broken piston skirt or wristpin bad maybe? But usually pulling the plug wires like you already did will usually tell you something. Lippy
     
  11. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    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!:mad:
     
  12. 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.
     
  13. yup.check for broken flexplate around crank bolts.common.
     
  14. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    Dude..... I replaced it a few posts ago.
     
  15. nutajunka
    Joined: Jan 24, 2007
    Posts: 1,466

    nutajunka
    Member
    from North Indy

    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.
     
  16. nutajunka
    Joined: Jan 24, 2007
    Posts: 1,466

    nutajunka
    Member
    from North Indy

    Did you check the crank end play when you changed the flexplate?
     
  17. amx180mph
    Joined: May 11, 2011
    Posts: 156

    amx180mph
    Member

    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.
     
  18. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    Yea, that sucker was solid. I only have one belt. Took it off and still noise.
     
  19. Nobody reads
     
  20. Nailhead dodge roadster
    Joined: Jun 28, 2004
    Posts: 707

    Nailhead dodge roadster
    Member
    from Cheney Wa

    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.
     
  21. nobby
    Joined: Jan 8, 2006
    Posts: 360

    nobby
    Member

    when you changed the trans, did you drop and dent the torque convertor
     
  22. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    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.:D
     
  23. F&J
    Joined: Apr 5, 2007
    Posts: 13,218

    F&J
    Member


    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
     
  24. Rickybop
    Joined: May 23, 2008
    Posts: 5,921

    Rickybop
    Member
    from Michigan

    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?
     
  25. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    No, but you made me think for a bit.:D
     
  26. henry29
    Joined: Sep 5, 2007
    Posts: 2,811

    henry29
    Member

    Maybe the oil pump pickup is loose?
     
  27. Commish
    Joined: Jan 9, 2010
    Posts: 379

    Commish
    Member
    from NW Ok

    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?
     
  28. Da Tinman
    Joined: Dec 29, 2005
    Posts: 4,226

    Da Tinman
    Member

    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.
     
  29. "T'RANTULA"
    Joined: Aug 6, 2011
    Posts: 658

    "T'RANTULA"
    Member
    from Ohio

    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...
     
  30. 1ton
    Joined: Dec 3, 2010
    Posts: 355

    1ton
    Member

    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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