Blew up the 454 in the C30

Discussion in 'The BS Topic' started by Da_Raabi, Jun 24, 2019.

  1. wnmech

    wnmech Veteran Member

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    Maybe GM used different suppliers for parts. My 71 was born a Van Nayees car
     
  2. Phil G

    Phil G Veteran Member

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    Every SBC I've ever built got a double roller chain. Some of the originals were cracked between every tooth! Screw the noise...
     
  3. tom3

    tom3 Veteran Member

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    Would the big block be an interference engine? Can the valves actually hit the pistons? Kind of wondering if there's something else going on there. Keep us posted.
     
  4. Da_Raabi

    Da_Raabi Veteran Member

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    Oh yes. Today I verified that the 1986 Chevy 454 is, in fact, an interference engine. The pushrods were all removed so, assuming all of the valves are fully closed due to spring pressure, I attempted a compression test. I pulled all of the spark plugs then started rotating the engine. All three pistons I tested (I gave up after that) would not build any pressure, and you could hear the air POURING through the valves. Literally a loud whooshing sound. It would build a little resistance to the turning, then you could hear all the air let out.

    My assumption is I bent the hell out of a bunch of valves, on top of the bent pushrods I already found.

    It's looking like the next step is to get the engine on a stand and get the heads off. I think I know what I will find though.

    If only I had the $6700 for a GM Performance 454HO. 425hp/500+ torque would be nice.
     
    1980RS likes this.
  5. Shizzle

    Shizzle Veteran Member

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    Damn the 454HO is $6700?
    I paid $4200 for mine back in ‘04 or ‘05.
     
  6. 1980RS

    1980RS Veteran Member

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    I think just the intakes will be bent as the exhaust valves have over .300 with flat top pistons.
     
  7. Mike N

    Mike N Administrator Staff Member Lifetime Gold Member

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    With all the pushrods out, I'd be surprised if any cylinder could build pressure. You're not letting any air in to the cylinder to compress since the intake valve can't open.

    What you really need to do is a leakdown test...... use the adapter from your compression tester and pump compressed air into the cylinders..... see if the air escaped thru the intake or exhaust to determne if the valves are sealing or not.
     
    76z28 likes this.
  8. 76z28

    76z28 Veteran Member

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    This, in order to build compression, you need to have something to compress :)
     
  9. budro6968

    budro6968 Veteran Member

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    My 74 C-20 454 had the same thing happen. When it went I was on the gas. The engine RPM Jumped way up for a couple seconds and then made a funny sound like a cartoon motor as it came to a stop. When I got it home I tore it down. The chain was in the oil pan my cam gear looked like yours and half the teeth on the crank gear were sheared off. None of my push rod or valves bent. I dropped the oil pan and cleaned out the chunks of Nylon and crank teeth. Replaced with a new Timing set. Buttoned it up and it started right up. That was about 15yrs ago. The old girl still runs good for it's age.
     
  10. Da_Raabi

    Da_Raabi Veteran Member

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    Ha! I knew I was missing something with this test. I noticed a loud "whooshing" noise during parts of the rotation. I thought it was air escaping out through the valves, but as you say - there was no air to escape. I wonder if it was actually air being pulled into the cylinder by the piston.

    Looks like additional testing is needed.
     

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