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Thread: strength of ally v steel

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    Default strength of ally v steel


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    Question for those steeped in metalurgy knowledge and wisdom ....

    I have a couple of engine mounts on the AT made from ally. They bolt to the engine and frame. The ally is 5mm thick - how thick would steel have to be to match its strength?

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    Should Get Out More Derek Badger's Avatar
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    Default Re: strength of ally v steel

    My first question would be...why are you changing them? Manufacturers chose materials for other reasons than strength. Stiffness for instance, which will have an impact on the flex in the chassis and in turn the ride characteristic.

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    Should Get Out More Julian_Boolean's Avatar
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    Default Re: strength of ally v steel

    About 3mm, but it depends on what grade of steel you use.
    What's wrong with the ally mounts?
    Have you lost one?
    Also ally has less flex than steel, you're question is a bit "I've got 7 beans, how many bananas do I need to replace them?"

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    Default Re: strength of ally v steel

    I suspect someone with enough knowledge of the application and materials could give an accurate answer.

    I suspect there's about nine types of 'strength' and more types of steel and aluminium alloy.

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    Default Re: strength of ally v steel

    Thicker than some nice Ti

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    Default Re: strength of ally v steel

    Quote Originally Posted by Derek Badger View Post
    My first question would be...why are you changing them? Manufacturers chose materials for other reasons than strength. Stiffness for instance, which will have an impact on the flex in the chassis and in turn the ride characteristic.
    Because they are made of Honda cheese and corroded beyond reasonable use. I can form steel easier than ally.

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    Default Re: strength of ally v steel

    In that case if it were me I'd use steel the same thickness as the alloy, it'll save having to compensate for the gap left.

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    Default Re: strength of ally v steel

    Quote Originally Posted by futter View Post
    Because they are made of Honda cheese and corroded beyond reasonable use. I can form steel easier than ally.
    To be honest, unless you're an engineer by trade (and if you're asking about material properties I'm wagering no) I'd replace with genuine. After all they are a pretty crucial part.

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    Default Re: strength of ally v steel

    Try cmsnl or David Silvers for old Honda parts
    David Silvers has the disadvantage of being at Leiston

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    Default Re: strength of ally v steel

    Quote Originally Posted by Derek Badger View Post
    To be honest, unless you're an engineer by trade (and if you're asking about material properties I'm wagering no) I'd replace with genuine. After all they are a pretty crucial part.
    What's the worst that could happen?

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    Default Re: strength of ally v steel

    Quote Originally Posted by Horse View Post
    What's the worst that could happen?
    Dunno, but we need to make sure he wears a GoPro on the shakedown run!

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    Default Re: strength of ally v steel

    Quote Originally Posted by Derek Badger View Post
    To be honest, unless you're an engineer by trade (and if you're asking about material properties I'm wagering no) I'd replace with genuine. After all they are a pretty crucial part.
    Quote Originally Posted by Horse View Post
    What's the worst that could happen?
    Quote Originally Posted by Derek Badger View Post
    Dunno, but we need to make sure he wears a GoPro on the shakedown run!
    Having done this sort of thing on occasion, and having done the calcs a few times, there are a couple of things to keep in mind. First off, the strength isn't going to be an issue, it will be the stiffness. A piece of 5mm ally is ~150% stiffer than a 3mm piece of steel, because there's a d^3 in the stiffness equation that overcomes the difference in Youngs modulus (the material stiffness). Whether or not that matters depends on the geometry of the mount and which way it's designed to support loads. Fatigue is the other big variable, ally will eventually fail, steel won't IF you keep the stresses below the endurance limit. It's usually fatigue that kills bike parts, especially around the engine. The worst that could happen is the mount starts to crack, if you keep an eye on it the safety risks are trivial, and lower than using badly corroded OEM items, which are likely cast, and will generally have worse material properties than plate.

    If it was me, I would go with 3mm steel and see what happened, if it was a bit vibey (due to lack of stiffness) I would weld in a new web or remake in heavier plate with a few lightening holes. Use some cardboard for templates, and don't leave any sharp re-entrant corners, because that's the sort of detail that starts cracks. Chuck a pic up if you want a bit more detail, but a single failed engine mount isn't going to kill you even if you get it really badly wrong.

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    Default Re: strength of ally v steel

    Quote Originally Posted by Big Pete View Post
    ...a single failed engine mount isn't going to kill you even if you get it really badly wrong.
    What about two failed engine mounts?

    Quote Originally Posted by futter View Post
    ...I have a couple of engine mounts on the AT made from ally...

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    Default Re: strength of ally v steel

    Quote Originally Posted by saga_lout View Post
    What about two failed engine mounts?
    It's not going to kill him, I once raced someone elses CR250 and found out afterwards that the engine was only held in by jubilee clips and the swingarm pivot bolt.

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    Default Re: strength of ally v steel

    It depends on the grade of ally and the grade of steel, the heat treatment state, etc. As a rule of thumb ally is half to a third the strength of steel of the same gauge and less fatigue resistant, though in 3-dimensional structures it can be as strong or stronger per weight due to the stiffness of the structure spreading the load. In your place I'd either get them powder coated or look into home anodising of the standard bits.

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