1925 Steam Wagon Crankshaft fitting detail
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  1. #1
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    Default 1925 Steam Wagon Crankshaft fitting detail

    Hi

    Attached is part of the factory drawing for a 1925 Steam Wagon crankshaft. I want to make a new reproduction crankshaft.

    The crankshaft is made in two parts. It has to be 2 parts because eccentric cams to drive the valve gear are fitted on the shaft between the crank webs. Very occasionally the crankshaft will need to be disassembled for maintenance/rebuild.

    The drawing shows the end crank and web attached to the shaft with a key (circled in red). The drawing does not define the fit between the web and the shaft. Most likely a press or shrink fit.

    My question: Is there a better way to connect the two parts of the crankshaft?? Perhaps a tapered fit clamped in place with a screw and washer down the centre of the shaft. Is there a better alternative to the key?


    crankshaft-detail.jpg

    Dazz

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    Curtiss Wright liked the clamp fit deal on flying machine radial engines

    The bolt was tightened until the specified STRETCH was obtained
    Attached Thumbnails Attached Thumbnails crank-direct-drive.jpg   wright-bolt.jpg  

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    Quote Originally Posted by johnoder View Post
    Curtiss Wright liked the clamp fit deal on flying machine radial engines

    The bolt was tightened until the specified STRETCH was obtained
    I can see the benefits of the Curtiss Wright clamp. It is not obvious from the drawing of the steam wagon crankshaft but right where the clamp bolt would pass is a threaded hole in the crank web that connects the eccentric to the crank.

    I basically need a solution that will fit within the current shape/form of the crankshaft. Any significant changes will have a domino effect. Change A requires changes to B, C and D etc.

    Dazz

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    Lots of old cars have built up cranks...Bugatti GP engines had roller bearing big ends on the rods......
    They used a tapered flat cotter like a bicycle crank cotter only bigger.
    Pin is applied at right angles to the crank pin. Applied using a press and 8-10tons, then a retaining nut applied to hold everything in place....
    Crank phasing is controlled by carefully grinding the taper on the cotter...

    Other cranks are just done with self locking tapers and a center thread to pull it up tight....
    Generally have a key , but that is just for timing and ease of assembly.....the taper does all the work.


    Assembled crank shot....note the retaining nuts and the end of the cotters



    Another shot of an assembled crank. Webs between rod and main pins are rectangular blocks cross drilled fro the pins

    Cotter (used)



    Tapered flat...adjust angle to "phase" throws.



    Cheers Ross

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    Quote Originally Posted by AlfaGTA View Post
    ...

    Other cranks are just done with self locking tapers and a center thread to pull it up tight....
    Generally have a key , but that is just for timing and ease of assembly.....the taper does all the work.

    ...

    Cheers Ross
    This looks like the best option for the steam wagon crankshaft.
    Rather than using a key for alignment, I am thinking of using a dowel. I can phase and fit the crank, then drill the hole for the dowel in a single op. Easier than cutting two key ways.

    Dazz

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    Quote Originally Posted by johnoder View Post
    Curtiss Wright liked the clamp fit deal on flying machine radial engines

    The bolt was tightened until the specified STRETCH was obtained
    The old Triumph (bike) twins big ends were torqued to a stretch figure, I'm probably wrong but 0.015'' rings a bell.

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    Quote Originally Posted by Limy Sami View Post
    The old Triumph (bike) twins big ends were torqued to a stretch figure, I'm probably wrong but 0.015'' rings a bell.

    April 1934 Manual sez .005 minimum and .005 maximum stretch. But then that is one whopper of a bolt - if I recall, had to acquire a 1 9/16 box end to fit the hex. It was one of those wrenches that was sold with a fitted cheater bar - so you could lean like the dickens on its 4 foot length

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    Erm-no it doesn't. Several makers fitted the eccentrics between HP and LP cranks. Split Eccentrics instead of split crank.

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    Quote Originally Posted by TedinNorfolk View Post
    Erm-no it doesn't. Several makers fitted the eccentrics between HP and LP cranks. Split Eccentrics instead of split crank.
    And I've made a full size split eccentric for a steam engine / pump and it's matching strap, …………..long long time ago and it was a replacement part ...and while I can't remember what it was for exactly, ………though I'm almost certain it would have been for one of the Kent Thames side papermills, as they were about the last bastions of steam.

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    Quote Originally Posted by TedinNorfolk View Post
    Erm-no it doesn't. Several makers fitted the eccentrics between HP and LP cranks. Split Eccentrics instead of split crank.
    The plans show solid eccentrics. They are too narrow to split, and there isn't the room to make them wider.
    The need to keep within the existing part envelope allows for a very limited range of solutions, no matter how good they might be.

    Dazz


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