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Engine Probs (2nd broken skirt maybe, oil pan is off, hissing noise) HELP!!!!

Discussion in 'The Garage' started by dawson444, Nov 28, 2003.

  1. dawson444

    dawson444 1/2 ton status

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    Alright, here is the deal.....

    A few months ago I pulled my engine out (less than 5k miles on it, its a GM 350HO). There was a broken skirt on a piston, I replaced the piston, GM parts guy said he thought it was just bad casting. Well, now the kock is back.

    I have pulled off the oil pan, and it looks like a skirt might be broken off again, except I can't remember which piston I replaced (stupid I know), it might be the one that is broken again, I'm not sure. The thing is though the "break" on it looks so clean and straight, like it suppose to be there, but I don't think it is. I also can't find the piece. I didn't find the piece of the other one though until I had the enigne out for a few days and had taken it 1/2 apart. Any tips?

    Also when I turn the engine over by hand I can hear some hissing noise coming from the bottom end b/c the oil pan is off. I don't think this is normal.

    Sorry for the novel, any ideas? Thanks!
     
  2. RustBuket

    RustBuket 1/2 ton status

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    I beleive the hissing would be compression escaping from the ring gaps...? Sounds like you're not having much luck and that the piston itself may not be your problem. Is your engine maybe badly out of balance? Detonating on that cylinder? Just shooting off some ideas. /forums/images/graemlins/confused.gif
     
  3. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Did you ever mic that cylinder? Sounds like excessive piston to wall clearance is making that piston rattle in its bore enough to break the skirt.

    I'd be returning that for a warranty motor if it's knocking. I would have never fixed it in the first place.
     
  4. dawson444

    dawson444 1/2 ton status

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    Thats what I'm wondeirng that it might be. I tried the warranty thing, but since it was a performance engine, it only had a 12mo 12k mile warranty. I had had it for 18 months when it happened the first time, but only 5k miles, the dealer wouldn't do anything.

    Any ideas on the hissing noise? Is that normal? Thanks!
     
  5. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Hissing noise is fine
     
  6. HarryH3

    HarryH3 1 ton status Author

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    The hissing is just compressed air leaking past the gaps in the rings. Nothing to worry about. /forums/images/graemlins/cool.gif
     
  7. dawson444

    dawson444 1/2 ton status

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    This might be a stupid question, but all 8 of the pistons should all be 100% the same right?
     
  8. SF87K5

    SF87K5 1/2 ton status

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    Yes they should be all the same size. Whats up with your pistons now Dawson??
     
  9. dawson444

    dawson444 1/2 ton status

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    I think i broke a skirt off of another one. I wish I knew it is was the same one, I just can't remember which one I replaced for the life of me. I was thinking about just throwing the oil pan back on there and dealing with it later, but I think I am going to pull it and I guess strip it down to the block and take the block to a machine shop and have them look at all the cylinders, esp. the one that the broken piston came out of. /forums/images/graemlins/mad.gif
     
  10. 84_Chevy_K10

    84_Chevy_K10 Banned

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    You could always just pull the head and piston and mic it yourself.
     
  11. dawson444

    dawson444 1/2 ton status

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    But after I mic it, what then???
     
  12. 84_Chevy_K10

    84_Chevy_K10 Banned

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    [ QUOTE ]
    But after I mic it, what then???

    [/ QUOTE ]

    If this is not the same hole that you had problems with before, it's likely that you just got a bad batch.

    If it does turn out that there is too much piston to wall clearance, I suppose that's where you'd have to decide if it was time to take it to the machine shop to be bored.

    I think since all the GM PP blocks use NEW blocks, its pretty unlikely that someone over bored or honed it before it was assembled. I'm sure anything is a possibility, but I at least think you should check out your options before you spend the big bucks.

    You could always put a forged piston in that hole. They swell more. /forums/images/graemlins/eek.gif /forums/images/graemlins/rotfl.gif
     
  13. dawson444

    dawson444 1/2 ton status

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    Alright, I have been looking around in there some more. BOTH skirts are boken on one of the pistons!

    The things that I don't get are...

    1. Where did the pieces go???? I haven't pulled that much metal out of my pan, and the magnet always just has a little.

    2. WHY did this happen??? What can I do to fix if when I pull it, I don't think slapping another piston in there is gona cure it, but I don't know where to start besides putting a mic on it. PLEASE HELP!!!

    Thanks!
     
  14. SUBFAN

    SUBFAN 1/2 ton status

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    I would have the bores checked, and put 8 new Keith Black pistons in there....

    Look it over upon dissassembly, and try and determine what went wrong....
     
  15. sandy78

    sandy78 Registered Member

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    I know it's only a 350, but could the piston skirt contact the cranshaft counterweight when heated to operating temp? When I built my 383, I had to custom contour the counterweights to clear the piston skirts. I used large paperclip wire as a "feeler" and haven't had any problems in 2 years of running.
     
  16. dawson444

    dawson444 1/2 ton status

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    Thats a REALLY good point to point out, b/c even with part of the skirt broken, it comes VERY close to the crank. So, now my usual question, what should I do to check that? Thanks!
     
  17. sandy78

    sandy78 Registered Member

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    I used a piece of wire (paperclip) about .030"dia. to check for clearance between the piston skirt and the crank at their closest position.
     

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