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possibility of a bottom end screw up breaking timing chain ?

Discussion in 'The Garage' started by R72K5, Oct 21, 2003.

  1. R72K5

    R72K5 Banned

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    how possible could it be for something like a broken rod- or anything else that could stop a bottom end from turning only at one spot- to cause a timing chain to break ?
    ive got a '90s 60 degree v6 engine in which the timing chain broke during cranking and ive removed one cylinder head only to find no bent valves so far, and the engine still turns by hand at the crank only so far to the same spot and locks solid, engine ran fine and did ll this during restart just after being parked, was daily driver and reliable

    i measured and compared height of all the valves and all of them are all the way up, none are stuck down, in either head.


    so hmm..

    whats anyone think ?
    bottom end screwed up ?

    thanks
     
  2. 99firehawk

    99firehawk 1/2 ton status

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    Coolant in the oil? how do the plugs look, things I would check before I started to tear off the heads (less there was a window in the block) But if your turning the crank and not the cam you couold be getting piston to valve contact.
     
  3. SWAMPRNR

    SWAMPRNR 1/2 ton status

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    Had a similar problem happen to one of my cars.
    The top of the piston came apart and turned sideways in the bore.The lower half was still on the rod so it just locked the motor when that piston came up.
    She had just went to the store came out and it wouldnt turn over.
     
  4. R72K5

    R72K5 Banned

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    [ QUOTE ]
    Coolant in the oil? how do the plugs look, things I would check before I started to tear off the heads (less there was a window in the block) But if your turning the crank and not the cam you couold be getting piston to valve contact.

    [/ QUOTE ]

    no, cam still turns fine, i tried turnign crank over by hand with chain removed and does same thing,b ut if i move cam a little bit then crank will clear and turn restof way, which made me thing valve bent, but one head is off and other head has valve retainers at correct height- all way up with rockers removed, no valves are bent,
    no water in oil, no bad plugs, no nothing, it ran perfect until warm restart that day, said he heard bang and noise when crankign engine, i assumed chain breakage did that, but apparently soemthing caused that to happen.



    so hmm..

    thanks
     
  5. R72K5

    R72K5 Banned

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    [ QUOTE ]
    Had a similar problem happen to one of my cars.
    The top of the piston came apart and turned sideways in the bore.The lower half was still on the rod so it just locked the motor when that piston came up.
    She had just went to the store came out and it wouldnt turn over.

    [/ QUOTE ]

    crazy stuff.

    thanks /forums/images/graemlins/laugh.gif
     
  6. MarcS

    MarcS 1/2 ton status

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    How about pulling the plugs out, get a piece of wooden dowel,(say 1/4 inch by 6 inch long)and put dowel into plug hole onto the piston. Have somebody turn the crank again and see if the piston is pushing the dowel up & down. Then try the next cylinder. At least this way you don't have to pull the heads and it might help determine if a rod or something is broke /forums/images/graemlins/thinking.gif
     
  7. R72K5

    R72K5 Banned

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    welp, i got the ":rear" cylinder head removed just now,and well i see whats wrong now,

    #3 exhaust valve head busted off and flippedover and imbedded into the piston, also took a chunkout of the cylinder head at end of the spark plug threads.

    how in the heck can a valve break off in aperfectly good running and clean engine ?? theres very little tiny amountof carbon in the engine, was taken care of you can tell by looking around inside,

    my next Q is about fixing this, would there be anything wrong with just repairing this by getting another std piston and std bearings for that rod, and another cylinder head and gasket set ?

    and are 3.1L head bolts re-usable, or one time stretch only ? store says that bolts come with head gasket set, so i assume one time use only ?

    another engine would cost morethan i want to put in this car, fixing this engine wouldbe about half that, ive got enough in the car already.

    thanks
     
  8. kennyw

    kennyw N9PHW Premium Member

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    Last engine I had that did this had a bad rust spot on the cylinder wall. It would turn over until the rings hit the rusty spot.
     
  9. R72K5

    R72K5 Banned

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    thats pretty crazy
    that engine must have been sitting in direct rain, or ?

    hmm
     
  10. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    GM was notorious for using selective fit bearings. If there are selective fit bearings in that engine and you replace them with standard bearings you will probably have low oil pressure and or a low end knock from excessive clearances. Yes that engine uses torque to yield bolts and must be replaced when removing the heads.
     
  11. mudjunkie 82

    mudjunkie 82 1 ton status GMOTM Winner

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    maybe the valve seized in the guide and the piston hit it or the valve timing was off?
     
  12. R72K5

    R72K5 Banned

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    [ QUOTE ]
    GM was notorious for using selective fit bearings. If there are selective fit bearings in that engine and you replace them with standard bearings you will probably have low oil pressure and or a low end knock from excessive clearances. Yes that engine uses torque to yield bolts and must be replaced when removing the heads.

    [/ QUOTE ]

    selective fit ?
    so this is beyond just normal std., .010, .020, .030 ?

    i want to find out more about this selective fit bearings thing

    thanks
     
  13. R72K5

    R72K5 Banned

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    [ QUOTE ]
    maybe the valve seized in the guide and the piston hit it or the valve timing was off?

    [/ QUOTE ]

    the only way valve timing could be off is if the chain was broken or gears not aligned right, i figured that maybe a valve or two or more could bend over when timing chain was broken, but to have a valve head just break off the stem ?

    wierd..

    thanks
     
  14. 99firehawk

    99firehawk 1/2 ton status

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    [ QUOTE ]
    but to have a valve head just break off the stem ?

    wierd..

    thanks


    [/ QUOTE ]


    how about this pic1
    or this pic 2
    Pictures off my 4000 mile all fordged dart headed blower motor that just had a valve brake off at the stem, killed a piston, a rod, the cam, 2 push rods, the block, the head the oil pump, 2 lifters, and my intrest in my car.
     
  15. R72K5

    R72K5 Banned

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    [ QUOTE ]
    [ QUOTE ]
    but to have a valve head just break off the stem ?

    wierd..

    thanks


    [/ QUOTE ]


    how about this pic1
    or this pic 2
    Pictures off my 4000 mile all fordged dart headed blower motor that just had a valve brake off at the stem, killed a piston, a rod, the cam, 2 push rods, the block, the head the oil pump, 2 lifters, and my intrest in my car.

    [/ QUOTE ]


    damn....
    crazy
     
  16. mudjunkie 82

    mudjunkie 82 1 ton status GMOTM Winner

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    [ QUOTE ]
    [ QUOTE ]
    [ QUOTE ]
    but to have a valve head just break off the stem ?

    A guy in town here built a bad-ass harley motor and had the same thing happen, It was a manley valve,the head came right off and totaled the whole motor....


    [/ QUOTE ]


    how about this pic1
    or this pic 2
    Pictures off my 4000 mile all fordged dart headed blower motor that just had a valve brake off at the stem, killed a piston, a rod, the cam, 2 push rods, the block, the head the oil pump, 2 lifters, and my intrest in my car.

    [/ QUOTE ]


    damn....
    crazy

    [/ QUOTE ]
     

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