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Thread: 420 chain FAIL

              
   
   
  1. #1
    teddillard
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    420 chain FAIL

    OK, there's been a lot of discussion back and forth about 420 chain, and I know a few people I really respect use it, and have had no issues with it, in spite of a lot of heavy use.

    Still.

    Obsessed as I am with weight, I can understand the effort to cut weight by using 420 chain, but I don't feel it's a safe place to do so. I don't know of any motorcycle over 100cc that used 420. I can't understand why people feel they can skimp on this area, when the consequences of failure are so dangerous. (Ever seen a chain break on a bike? I have.) At the very least, the smaller chain wears faster. Maybe not too fast for your use, but it, undeniably, wears faster.

    I have been fairly content to sit back and chalk it up to opinion, until I saw this:



    This is from a Ninja 250 conversion with an AC20 and lipo, and it happened in normal use, on the street, while "hitting the throttle up to around 600amps". I think it was a McMaster Carr sprocket, but it really doesn't matter. If the type of sprocket is critical while using a drive chain size, then to my thinking, the drive chain is too small.

    ...and that, kind sirs, is my opinion.

  2. #2
    Senior Member jonescg's Avatar
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    It is a rather small sprocket isn't it. Personally I would never go lower than 428 pitch chain. 520 for any big bike.

  3. #3
    Senior Member picaroon's Avatar
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    I'm guessing but it looks like it could be an 11 tooth sprocket, which means there could also be a good argument to have a larger front sprocket. A 12 or 13 tooth sprocket would have to be a larger diameter and so its wall thickness would be greater and have more strength.
    Which broke first? Chain or the sprocket?

    sounds like a chicken or the egg question!!

  4. #4
    Old EV Racer EVcycle's Avatar
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    600 amps! well of course.

    Each application needs what is best. I would not run 420 chain on a 600 amp unit
    (and most likely a 400+ pound bike?) either.

    I would not waste 530 on a 320 pound 400 amp max motorcycle.
    We ran 530 on the drag bikes as that was what that application needed.

    I also do not consider this skimping. I researched what was best for OUR project as
    everyone should do for their project. I see 420 on the production EV motorcycles.

    Are they just being cheap?

    630 for everyone!
    Last edited by EVcycle; 28 June 2012 at 0754.
    EV Ed
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  5. #5
    Senior Member Remotecontact's Avatar
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    That's my sprocket up there. My bike weighs about 315lbs. This was caused by an undersized front sprocket. It is an 11-tooth http://www.mcmaster.com/#cadinlnord/6280k654/=i6b77q . This was a design error by me and the chain is still in good shape. Look at the CAD of the sprocket. With the step down in the hub for the chain combined with the keyway there is about 1/16" of steel there. I don't think they should even sell those 11 tooth #40 sprockets with a 7/8" bore. Upping it up to 12 or 13 teeth greatly increases the amount of meat above the keyway (where it broke) http://www.mcmaster.com/#cadinlnord/6280k674/=i6b8br . Also this was a standard unhardened mcmaster sprocket.

  6. #6
    Senior Member billmi's Avatar
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    So the chain size is why the wall of the sprocket's base (which is a similar thickness between sprockets of different size) split in two?
    I would think if the chain was too small or weak, the chain would have broken instead of the sprocket and it's base.
    Maybe I'm missing something in the big picture.
    Sensei - Electric Ninja 250

  7. #7
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    Maybe we should use the size chain and sprockets on a 60" HD Agric tiller I'm working on today at the fab/repair shop:
    Picture.jpg
    It's a 1.5" pitch chain. Compare it to the 41 chain and sprocket, also in the pic.

    The tooth faces of the smaller sprockets are usually heat-treated(hardened) to reduce wear. Sometimes, the treatment on the smallest sprockets extends through to the bore-making it more brittle and prone to this kind of breakage.

    This is another reason, along with increased wear, noise, and shaft/bearing loads, not to use too small of a sprocket.

  8. #8
    Old EV Racer EVcycle's Avatar
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    Now that is a MANLY chain!!!!
    EV Ed
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  9. #9
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    I've split 12t front 420 sprockets like that. The sintered sprockets are fragile, the ones machined from bar-stock don't split and last a long time.

    A fresh renthal #420 chain lasts a single event with my bicycle before it's worn out. Start out the day taking it out of the wrapper all beautiful and factory greased, and connect it up, end the day with a chain so worn out it sags on rear sprocket. It also requires re-tensioning after about every session, and it wears the little areas the pin's ride enough to grow and get sloppy after each 10minute riding session. (I run about 3-4x the power through it than it was designed for, it lasts fine at lower power levels) Kinda a pain in the neck the constantly have to be replacing and fiddling with, but going to #520 (which would last forever) would add a lot of weight and sprocket diameter.



  10. #10
    teddillard
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    Quote Originally Posted by billmi View Post
    So the chain size is why the wall of the sprocket's base (which is a similar thickness between sprockets of different size) split in two?
    I would think if the chain was too small or weak, the chain would have broken instead of the sprocket and it's base.
    Maybe I'm missing something in the big picture.
    Small chain = small sprockets, right? Yes, I'd think that too (that the chain would break instead of the sprocket) but I've never heard of a motorcycle sprocket breaking before. ...kind of my point.

    Exactly, Luke- for a race bike, it only has to last one race. For a daily ride, it's a different set of goals.

    Looking back on this post, maybe my title seemed more strident than I intended. (I was going for wit, but it's hard to come by at 5AM.) However, it is a very important thing to discuss I think, and I appreciate the contributions...
    Last edited by teddillard; 28 June 2012 at 1347.

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