Bad Big Ends
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Thread: Bad Big Ends

  1. #1
    Fellow Frogger! WAUTY205's Avatar
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    Icon4 Bad Big Ends

    Hi all,

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    Just asking anyone who might know the cause of this sort of damage. They are the bottom big end bearings but the top bearings are just scored! Very strange I thought. It's been about 6mths since full rebuild. Oil pressure was OK until now. Frequently at high revs I imagine. We have some ideas but any help would be appreciated.
    It's out of my cousins friend's car, I won't say what, as it's not French .
    -Will
    Attached Thumbnails Attached Thumbnails Bad Big Ends-bearing-failure-1.jpg   Bad Big Ends-bearing-failure-2.jpg  
    1990 205Gti
    1976 504 rally car (currently out of action)

  2. #2
    1000+ Posts Gamma's Avatar
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    It looks like they were not fitted correctly in the first place.
    The RHS shell has been hammered and could be indicative of being too loose.
    It is hard to tell from these photos as to the extent of heat damage or oil feed failure, as the worst of the damage could have occurred at the time of failure.
    Was it only one set or are they all like this.
    If it is only one bearing shell set, then I would guess single oil gallery feed failure, (read-crap in hole to bearing).

    If a new engine has had the [email protected] revved out of it before having been properly "RUN -IN" then this could result in premature failure, (but you would expect signs on other parts. Was the bottom end fully re-built with the rest of the motor, (often a re-build can mean rings only or may include big ends and or Mains to).

    How are the Mains?

    Interesting!!!
    Last edited by Gamma; 12th July 2005 at 04:17 PM. Reason: The other Left.
    /// 1986 SII 505 GTI
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    Moderator Alan S's Avatar
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    Name the oil they were using in it...if you're game. It looks like it's been run on water

    My guess would be a total lack of lubrication that has caused the white metal to almost melt, although normally I'd expect the metal to be looking a bit blue and showing signs of rolling up in the direction of the engine's rotation.

    At face value, you'd have to say the bearing was left out in the weather as it almost looks like corrosion, but another thought is, were the holes in the conrod aligned with the ones in the bearings?


    Alan S
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    1000+ Posts Haakon's Avatar
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    crank ground and the wrong size oversize bearings fitted? Top shell has power stroke forces to keep it in contact with crank more, and left most of hammering from what would be excessive clearances confined to the bottom shell. And if the crank has been ground, not cleaning out the gallery is a big no no - there always swarf and crap in them when you get it back from the engineering places..... I always take the crank to the car wash and seriously blast them out (and very quickly dry it!) before it goes in the motor.
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

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    1000+ Posts robmac's Avatar
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    Default cause

    Quote Originally Posted by WAUTY205
    Hi all,

    Just asking anyone who might know the cause of this sort of damage. They are the bottom big end bearings but the top bearings are just scored! Very strange I thought. It's been about 6mths since full rebuild. Oil pressure was OK until now. Frequently at high revs I imagine. We have some ideas but any help would be appreciated.
    It's out of my cousins friend's car, I won't say what, as it's not French .
    -Will
    HEAT

    OIL STARVATION

    Probably amongst the worst I've seen....

  6. #6
    Fellow Frogger! 123abc's Avatar
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    hmm, whatever caused it, (lack of oil/contaminated oil) looks like it got bloody hot.

    reving out a new engine will destroy it quickly, those bearings need to be babied for a while to allow everything to settle in its place.

  7. #7
    Fellow Frogger! WAUTY205's Avatar
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    Thanks for all the help guy's!
    Just got an email from my cousin & it turns out that the realy bad bearings were the rod end bearings not the cap end after all. THat makes a little more sense. Turns out the workshop who did the rebuild had to grind the crank heaps & had to use the thickest bearings available, or somthing like that. We are assuming they were still a little oversize.
    -Will
    1990 205Gti
    1976 504 rally car (currently out of action)

  8. #8
    1000+ Posts Haakon's Avatar
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    Quote Originally Posted by WAUTY205
    Turns out the workshop who did the rebuild had to grind the crank heaps & had to use the thickest bearings available, or somthing like that. We are assuming they were still a little oversize.
    -Will
    Sounds a bit dodgy to me.... You either use the RIGHT bearings, or you get another crank. You DONT use a "she'll be right mate" closest thing you've got... Time to find a reputable engine builder...
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

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    Gone Fishin' Ray Bell's Avatar
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    Originally posted by robmac
    HEAT

    OIL STARVATION

    Probably amongst the worst I've seen....
    This is oil starvation... left to right is one pair of shells... they were more or less okay. Next is the pair from No 3 big end, starting to pound after running dry and losing all their bearing material.

    The solo pic is No 1... the pounding and heat has led to the steel backing working its way around the edge of the rod, squeezing up between the rod and the crank sides. Very thin, very brittle.
    Attached Thumbnails Attached Thumbnails Bad Big Ends-bearingsclay1.jpg   Bad Big Ends-bearingsclay2.jpg  

  10. #10
    1000+ Posts Haakon's Avatar
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    Quote Originally Posted by Ray Bell
    This is oil starvation... left to right is one pair of shells... they were more or less okay. Next is the pair from No 3 big end, starting to pound after running dry and losing all their bearing material.

    The solo pic is No 1... the pounding and heat has led to the steel backing working its way around the edge of the rod, squeezing up between the rod and the crank sides. Very thin, very brittle.
    Crikey! I bet that was making some good noises...
    I tried to drown my sorrows in alcohol, but the bastards learnt how to swim

  11. #11
    Gone Fishin' Ray Bell's Avatar
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    Originally posted by Haakon
    Crikey! I bet that was making some good noises...
    Funny you should mention that...

    All I ever heard was, "Your engine's siezed! Come and get me!" on the end of the phone.

  12. #12
    1000+ Posts Gamma's Avatar
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    Quote Originally Posted by Ray Bell
    This is oil starvation... left to right is one pair of shells... they were more or less okay. Next is the pair from No 3 big end, starting to pound after running dry and losing all their bearing material.

    The solo pic is No 1... the pounding and heat has led to the steel backing working its way around the edge of the rod, squeezing up between the rod and the crank sides. Very thin, very brittle.
    The only time I have seen this kind of failure the motor was only making a significant hammering noise for about 2 min. I pulled over, (already knowing the problem was terminal), then it stopped as soon as the revs dropped. The only tear shed, was for the lost opportunity, of the date I was to attend, (not my car (company) and a total heap of c%@p at that). A Cup shell had slipped around in the cup causing the bolt to strip and the mains cap to deform, the hammering was the broken crankshaft bouncing around. Surprisingly the crankshaft was still aligned and all the pistons were moving, it only fell apart when stripped.
    Last edited by Gamma; 14th July 2005 at 09:01 AM. Reason: Good to see you back Ray.
    /// 1986 SII 505 GTI
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  13. #13
    Gone Fishin' Ray Bell's Avatar
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    That's not unusual... even in 3-bearing engines... the bits of crank still revolve together most times, from what I've seen.

  14. #14
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Ray Bell
    That's not unusual... even in 3-bearing engines... the bits of crank still revolve together most times, from what I've seen.

    Most times.

    That is until the the the two halves (mostly on 3MB cranks) come out of alignment or flex enough to allow a counter weight to hit the bottom of a liner.

    This usually results in ventilated block, lubricated engine compartment. In the worst case the conrod , after holing the block, keeps rotating cuts the engine half (it stops rotating when it hits the camshaft)

    Collateral damage are a valves embedded into top of a pistons because the cam ceases to time the valves when it stops rotating after the timing chain breaks.

    This sequence of events happened to a 403 engine in my 203c.

    It is not a pretty sight.

  15. #15
    Gone Fishin' Ray Bell's Avatar
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    Where are the photos to illustrate these little experiences?

  16. #16
    Fellow Frogger! Ralph's Avatar
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    I once had a 2.5 PI MkII Triumph that was of the twin crankshaft variety. I was thrashing it through the Bobbin Head Rd. heading towards Mt. Colah when it started making a horrible noise. I turned around and managed to drive it all the way back to my then home at Concord West. The crankshaft had snapped clean through the bearing between no. 2 and no. 3 cylinders. I heard afterwards that this was a common fault on these cars later in their life as the Lucas Mk II fuel injection system used to wear and cause more fuel to be delivered to the rear four cylinders than the front two and cause the crankshaft to weaken at that spot over time. A good solid thrashing would cause it to snap.

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  17. #17
    1000+ Posts robmac's Avatar
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    Quote Originally Posted by Ray Bell
    Where are the photos to illustrate these little experiences?

    .... welly before the days of digital imaging, more in he time of Maymiya, Pentax and Nikon 126 large format cameras.

    Sad to Ray, during those days the joy and heartache was driving and fixin'em rather than "sharing the knowledge" (or disasters)

    But I can assure this did happen to my 203.

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