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Thread: crank nut

  1. #1
    Rods 'n' Sods Junkie supateach's Avatar
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    crank nut

    Hi all
    Hope everybody is keeping safe and well, have not posted for a long time, diagnosed with prostate cancer earlier this year, had it removed and have got the all clear now.
    Started to get a rattle from he top end recently, engine is '73 M30 BMW big six, thought it was tappets but when I checked timing chain was sloppy and adjuster is as far over as it goes, so I need new timing chain, sprockets ect. That isnt the problem, the crank nut will not have been off for more than 40 years so will be a b*tch to get off, and locking the engine while I swing on a massive bar to loosen it is the problem, there is a special tool which bolts on the bell housing and engages with he flywheel teeth. Dont want to just ram a screwdriver into the flywheel teeth, any suggestions as to how to lock the engine to get the nut off without a special tool,and any advice on getting the nut loose.
    Thanks
    Tony

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    Off the Xmas card list kapri's Avatar
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    Just make the tool, especially if you already have a picture of it ? The tool is normally bolted through a bell housing bolt and has a drop down V ( piece of angle iron) that locks into a couple of teeth.

    Sorry to hear about diagnosis and treatment but when caught early enough it is very survivable . Friend of mine hadsdone 12 years since diagnosis and he chose not to have surgery.
    Last edited by kapri; 12-07-2020 at 16:34.

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    Old school way was to take out a spark plug, turn the engine backwards and get the piston about halfway on the upward part of the compression stroke. Feed a long length of nylon rope into the spark plug hole and then continue turning the engine backwards until the rope jambs between the piston and the combustion chamber.
    https://www.youtube.com/watch?v=916MesBuShI

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    Official RnS Addict Magman's Avatar
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    Quote Originally Posted by NMNeil View Post
    Old school way was to take out a spark plug, turn the engine backwards and get the piston about halfway on the upward part of the compression stroke. Feed a long length of nylon rope into the spark plug hole and then continue turning the engine backwards until the rope jambs between the piston and the combustion chamber.
    https://www.youtube.com/watch?v=916MesBuShI
    That works really well.
    I used that method at a VW show many many moons ago when I’d broken a valve spring over-revving in 2nd on the strip. Fed a guy rope in, wound the engine over and it locked the valve in place so I could get the spring off without any fear of the valve dropping into the chamber.

    A method we’ve used a few times recently, and it only works if you’ve got plenty of access at the front, is to used a deWalt 950nm rattle gun. If you can borrow one of them it’ll spin the nut off without the engine turning over cos it has monster torque that will break the hold the bolt has before the engine can move.

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    Off the Xmas card list kapri's Avatar
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    Quote Originally Posted by Magman View Post
    That works really well.
    I used that method at a VW show many many moons ago when I’d broken a valve spring over-revving in 2nd on the strip. Fed a guy rope in, wound the engine over and it locked the valve in place so I could get the spring off without any fear of the valve dropping into the chamber.

    A method we’ve used a few times recently, and it only works if you’ve got plenty of access at the front, is to used a deWalt 950nm rattle gun. If you can borrow one of them it’ll spin the nut off without the engine turning over cos it has monster torque that will break the hold the bolt has before the engine can move.
    One my Rover 75 tdi ( BMW engine )we had to use a commercial vehicle wheel nut remover! Something like over 200lbs torque required.

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    I'm a grown up member now !
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    AustinHarley is offline
    I second the use of an impact wrench. Shouldn't need to lock the engine at all. Torque back up you'll probably still need to lock it though.

    I used one on an old VW crank that still had the flywheel attached.

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    Depending on how brave you are......

    I use an impact socket and a 3/4" drive "T" bar, and while I hold the socket in place with the bar about 6" away from either the chassis or the floor, I get someone to flick the starter. The bar spins that distance, hits the solid floor/chassis and undoes the crank bolt. If you remove the plugs you get even more of a spin. You definitely don't want the engine starting. I've never had this method fail, and i still have all my fingers. Only engines it won't work on are some Hondas, as they rotate anti-clockwise, anything that rotates the normal clockwise from the front will work. If it fails the first time, move the bar a bit firther away from the solid object.

  10. #8
    Rods 'n' Sods Junkie bully's Avatar
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    If you can't get hold of an impact wrench this may sound like a bit of a bodge but it should work put an impact socket on the crank nut and a breaker bar down to the floor and try to start it (you will need to work out which way it turns) it may take a couple of go but it will shock the nut of (just a side note I would remove the rad just it case the bar fly's of )

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    Rods 'n' Sods Junkie bully's Avatar
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    Should have typed quicker

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  13. #10
    Rods 'n' Sods Junkie supateach's Avatar
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    thanks, have ordered the parts, will try to get the nut off as soon as they arrive. Will let you know how it goes

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