403,a tricky one
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Thread: 403,a tricky one

  1. #1
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    Default 403,a tricky one

    Searching for a coolant leak I noticed a plug or some sort has dropped out of the block on the RHS below the rear pipe of the exhaust manifold. As access is difficult I am having trouble identifying the thread so I can plug it up.Please can anyone help?
    Woody

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  2. #2
    WLB
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    The coolant drain plug isn't screwed in. It's just a plug with a rubber washer that is held in by spring pressure. The 'spring' is a long steel rod that pivots lower down the block, and the plug slides on it. The top of the rod is located in a J-shaped slot in a metal plate near the manifold. It's very clever. You just slide the end of the rod around in the slot to take the pressure off the plug and it moves outward to allow draining. It's prevented from dropping out and sliding down the rod by an X-shaped inner end which doesn't normally come all the way out of the block. The plug is alloy and can corrode.

    I haven't looked at or worked on a 403 since the late '70s so this is all from memory.

    Check that you haven't accidentally moved the top of the rod in its slot, thereby releasing the inner pressure and pulling the plug from the hole.
    Check that the plug hasn't corroded and lost the protruding end the locates it in the hole in the block.
    Check that the rubber seal is still good.
    Check that the rod isn't bent and lost its springiness.

    Of course a previous owner may have removed all this original stuff, tapped the hole, and screwed in a conventional plug. In which case it's anyone's guess.
    But if it was me, I would have chosen an 1/8" or 1/4" BSP(tapered) brass plug as that is what would commonly be used in such an application.
    These are readily available from a plumbing and gas-fitting supplier so you could try one.
    Thread tapping bits are readily available if the thread is damaged.

    The ISO metric system for pipe thread sizes adopted the British BSP standard and the only difference is that its size is given in mm instead of fractions of an inch. For example, an ISO 25mm pipe thread is the same as 1" BSP.

    Good luck.
    Last edited by WLB; 23rd August 2014 at 10:59 AM. Reason: fix typo
    pugnut1 likes this.

  3. #3
    1000+ Posts Peter Chisholm's Avatar
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    You could be referring to the block drain plug. If so, it has no thread but seals due its rubber gasket being sandwiched between the spring loaded valve and the block.
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    1000+ Posts fnqvmuch's Avatar
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    WLB i must say that takes the cake as an answer; says it all and then some ...
    please see the att. as gilding the lily.

    noting this is the 203 type but near as dammit ...
    Last edited by fnqvmuch; 23rd August 2014 at 01:11 AM.

  5. #5
    1000+ Posts Peter Chisholm's Avatar
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    Glad that all seems sorted then!

  6. #6
    WLB
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    Thanks fnqvmuch, but if you'd seen me this afternoon trying to remember how the drive belt on my mower threads around all the pulleys, you might have reconsidered your opinion of my powers of recall. Thanks for the drawing.

    Peter, it looks like we both posted at virtually the same time.

  7. #7
    1000+ Posts Peter Chisholm's Avatar
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    Yes, mustve been typing together!
    As to why recall is good for old stuff, I have no idea but I am, obviously, not alone.

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