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Thread: 4 Bolt Mains.

  1. 17th July 2009, 10:16 AM #1
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    4 Bolt Mains.

    I was having deep discussion with another RR/LR nut the other day and the topic of 4 bolt mains came up.
    Can any one tell me the reason for them. I always thought it was purely for strength but this person suggested it could be to make the engine smoother.
    What RR/LR engines had 4 bolt mains?

    Dave.
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  2. 17th July 2009, 10:20 AM #2
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    I think the 4.0 and 4.6 had the 4 bolt mains.

    Therefore Disco 2 and RR P38 engines.
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  3. 17th July 2009, 11:22 AM #3
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    The D2 has them in the V8...I thought it was only for strength.

    Cheers
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  4. 17th July 2009, 11:35 AM #4
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    I also thought the 3.9 V8 changed to 4 bolt mains in about 97 - if so does anyone know what engine number the change happened with?

    Garry
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  5. 17th July 2009, 08:32 PM #5
    Bigbjorn
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    Four bolt caps, or cross bolted main bearing caps are used to add rigidity to the block-crankcase-main bearing carrier assembly. This helps stop crankshaft whip, keeps everything going up and down , round and round in proper alignment when using angry throttle openings.
    URSUSMAJOR
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  6. 18th July 2009, 03:25 PM #6
    RoverP6B
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    garycol wrote,..
    I also thought the 3.9 V8 changed to 4 bolt mains in about 97 - if so does anyone know what engine number the change happened with?

    Garry
    Hello Garry,

    The interim 3.9 litre engines from April 1994 till October 1998 featured 38A style main bearing caps, and the blocks were cast with cross bolting in mind, but the blocks were never factory drilled and the cross bolts were never fitted. Only the two verticle bolts were fitted.

    Ron.
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  7. 18th July 2009, 05:32 PM #7
    Traco
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    Problems with the bearing registers alignment and cracking around the bolt holes were evidently an issue with the earlier two bolt blocks, though in reality I don't think many failed because of it that were not being used in competition.
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  8. 18th July 2009, 05:49 PM #8
    Bigbjorn
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    Quote Originally Posted by Traco View Post
    Problems with the bearing registers alignment and cracking around the bolt holes were evidently an issue with the earlier two bolt blocks, though in reality I don't think many failed because of it that were not being used in competition.
    Has anyone ever fitted main bearing cap bridges, sometimes called "strongbacks" to them as an alternative to four bolt caps? This was normal practice with hghly modified sideplate Holden sixes.

    Chev small blocks with two bolt mains can be readily converted to four bolt mains by any decent machine shop. I have the drawings if anyone needs them.
    URSUSMAJOR
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  9. 19th July 2009, 12:52 AM #9
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    didn't the late moddle series 3 2.25 have 4 bolt mains?
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  10. 19th July 2009, 02:32 AM #10
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    sorry a little bit more resurch said that its a 5 bearing
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