Cam shaft sensor (speed sensor) => broken magnet
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  1. #1
    Senior Member johnste1960's Avatar
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    Cam shaft sensor (speed sensor) => broken magnet

    Hi all,

    Was doing the upgrade to the new sensors. Got the old one apart with no problems. carefully removed the magnets and placed them in a safe location (was warned by a fellow forum membe cautioned me not to break the magnet) WHen I went to put the part back together, I retrieved the magnets only to find one had broke almost exactly in half. There is a little alignment hold drilled partially in the magnet and the crack was right at that position. Not sure how it happened,




    a) If anybody has a spare magnet or a source where to obtain these, please give me a shout. THese are not even an individual part on the parts list as they are part of an assembly.

    b) Can I use the magnet as is with it broken, when I place them on the mounting bracket, they stick down good and I can push the two together so you can not even see the crack. when I put on the sensor, and put in the screws, they will stay in place. Howeer, I have been talking and researching magnetism theory. I am getting an understanding, but am not 100% certain of the effect. any input in this area would help.

    c) The new sensors come with a bracket and a magnet. you slide the sensor off of the bracket and iscard it and remove the bracket from the old sensor and slide it in. Can I just use the magnet that comes with the new sensor. It is about half the length, and rectangular instead of semi circular, but I think it will fit. The hole spacing is such that the holes line up with one of hte holes and the second hole goes right over the alignment dimple. what do you think

    New sesner removed from metal insert


    Here is the new magnet on the plate, Magenet is not quite as long, but I think it will fit, I probably could grind off the magnet to make it rounded, but not sure that is necessary as I think it fits in the housing this way.
    Last edited by johnste1960; 01-02-2017 at 07:48 PM.
    Current Bikes: cx500t1, cx500t2, cx500t3=UK version, cx650t 1979 CBX zx750E1 (750 turbo#1), zx750E2(750turbo#2 -parts bike but planning to completely rebuild), zx750E1(750turbo#3 -high performance build, shooting for 150HP), 1973 H1-500, 1974 H1-500, 1974 H2-750, 2014 BMW K1600GTL-Exclusive, 1984 Honda Interceptor 1000:blob10:


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  2. #2
    Super Moderator ramprat06's Avatar
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    Regarding your magnet question, I found this at Questions and Answers - What happens when a magnet is cut in two? Does the strength of an electromagnet depend on the number of turns of wire? If you have two magnets...

    A couple of different things can happen when you cut a magnet in half.If you do it gently you can end up with two magnets. You can think of a magnet as a bundle of tiny magnets, called magnetic domains, that are jammed together. Each one reinforces the magnetic fields of the others. Each one has a tiny north and south pole. If you cut one in half, the newly cut faces will become the new north or south poles of the smaller pieces. You could keep slicing smaller and smaller slices like a loaf of bread and keep getting thinner magnets, each with a new set of poles. Remember, I did say though you only get two magnets if you cut them gently. The magnetic domains in a magnetic material can be knocked loose, by bumping or vibrating the magnet (like when sawing it in half). If knocked loose, the domains are no longer arranged neatly, so they do not reinforce each other. If they are in a random orientation, with their fields pointing all over the place, they cancel each other out.
    Since the magnet is now two different poled magnets, even if you put them back together visibly, they will not have the same characteristics as a single magnet would. I don't know how much this would affect things at this level, but you are probably best served with the new ones.
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  3. #3
    Senior Member Pim205GTI's Avatar
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    The Goldwing GL1200 Aspencade has the same magnets and pickups



    Although Ramprat has a point. Because the North-South pole direction is going vertical / steel plate to steel plate and not going through the crack I think it will still work. But I am not sure........
    Last edited by Pim205GTI; 01-03-2017 at 04:07 AM.
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  5. #4
    Senior Member reclinedrelic's Avatar
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    Do the two broken pieces "stick" together? I.E. one face of the crack has become a S pole and the other a N pole. If that is the case the pieced together magnet might still work.
    Mike

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  6. #5
    Senior Member johnste1960's Avatar
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    Quote Originally Posted by reclinedrelic View Post
    Do the two broken pieces "stick" together? I.E. one face of the crack has become a S pole and the other a N pole. If that is the case the pieced together magnet might still work.
    Actually, with the break, each becomes two individual magnets. If you try to put them together the same way on say a wood table, they repel each other at the break acting like a S-S pole or N-N pole. If you force the two together, you still get a dipole magnet with one end of the piece being north and the other end being South. I found some info on the internet (if you can beleive that) from someone who seemed to be in the know that explains some sort of pole reversal. Personally, I have yet to understand this.

    I am an electrical engineer at an aerospace company and it brought about quite the discussion at work today. While electricity and magnetism are closely related, The courses I had many many moons ago (basic physics) either did not get into this sort of thing or I simply do not remember, LOL.

    Supposedly, I read on the internet that the magnetic strength of two magnets put together this way is 1/2 of the strength of the original magnet. If you want to take two magnets like this and get more field strength, supposidly you are suppose to put them together top/bottom versus side/side. Please do not have me explain it, this is what I am reading. Being an engineer, I am compelled to try to understand it deeper, LOL

    PIM205GTI states that the north south pole are going plate to plate, To be honest, that is something I did not condsider. I have to think about this. This may help explain and make me better understand the observations I am seeing.

    In any event, it is nice to know the magnets are the same as in the goldwing. This will give me more sources to check.
    Current Bikes: cx500t1, cx500t2, cx500t3=UK version, cx650t 1979 CBX zx750E1 (750 turbo#1), zx750E2(750turbo#2 -parts bike but planning to completely rebuild), zx750E1(750turbo#3 -high performance build, shooting for 150HP), 1973 H1-500, 1974 H1-500, 1974 H2-750, 2014 BMW K1600GTL-Exclusive, 1984 Honda Interceptor 1000:blob10:


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  7. #6
    Senior Member johnste1960's Avatar
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    There were a few people that came right out and said the broken magnet will not work. I am interested in hearing how they came to that conclusion. Did they actually try a broken magnet?

    I am wondering what exactly the magnet does. Some at work state it is a BIAS magnet.

    Based on my experience, if this magnet is removed, you will still get a current induced in the coil when the rotor is spinning. My hypothesis is that with the magnet in place, ( you know have a magnetic field in the center of the coil) you will get a larger signal.

    Personally, I am wondering more the signal processing circuitry and the software in the ECU as to what it takes to avoid a fault detection. If the software is comparing the differential signal between both coils, it may throw a fault because the difference in signals from each sensor may exceed a preset value in the Software. (this assumes what I read is correct and the broken magnet is 1/2 of the strength of the other magnet) If this is true, then I am assuming that the signal generated would be different in the coils perhaps in amplitude.

    another test would be that the signal from the individual sensor might be below some predetermined threshold.

    I have a 3rd bike I will be working on later, I may be inclined to run some experiments just to satisfy curiosity, LOL
    Last edited by johnste1960; 01-03-2017 at 06:07 PM.
    Current Bikes: cx500t1, cx500t2, cx500t3=UK version, cx650t 1979 CBX zx750E1 (750 turbo#1), zx750E2(750turbo#2 -parts bike but planning to completely rebuild), zx750E1(750turbo#3 -high performance build, shooting for 150HP), 1973 H1-500, 1974 H1-500, 1974 H2-750, 2014 BMW K1600GTL-Exclusive, 1984 Honda Interceptor 1000:blob10:


    Previous Bikes: CB500T, 1974 Kawasaki 900 z1, 1989 Yamaha Vmax, 2008 HD soft tail custom

  8. #7
    Super Moderator ramprat06's Avatar
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    It certainly is a valid and exhaustively intriguing discussion! Since the earth itself is a huge magnet, who knows what can happen in a given scenario on this scale.
    I would imagine the designers of the ECU (as well as the associated software) must have done intensive calculations to achieve the desired results for the motor. As such, the results have a rather narrow window of success. So any breach of that "window" would cause unwanted things to happen.
    Magnetic science is quite fickle. As my post above noted, a solid magnet is just a compound of myriad tiny individually magnetized particles.

    Have you ever rested a screwdriver or other ferrous object next to a solid magnet for any length of time? It adopts the magnetic properties from the source magnet, and translates those properties to its own molecular makeup. Same when using an electromagnet.
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  9. #8
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    the system is a hall effect so incorrect polarity of the magnet and the hall "gate" wont trigger at all

    if you need more in depth info ask rayman he lives this stuff every day

    HEY RAY care to comment?
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  10. #9
    Senior Member edinlr's Avatar
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    The closest I have gotten to an electrical engineering degree is to pay my light bill. Maybe two magnets will give you a dual spark, ha ha. It sounds like from the consensus it is best to replace it with the closest fit magnet you can get. It seems logical that our Euro buddies will have an answer since a low mileage bike for them is 80,000 km, where most bikes are parked here when they need a triple bypass.
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  11. #10
    Senior Member edinlr's Avatar
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    Quote Originally Posted by johnste1960 View Post
    There were a few people that came right out and said the broken magnet will not work. I am interested in hearing how they came to that conclusion. Did they actually try a broken magnet?

    I am wondering what exactly the magnet does. Some at work state it is a BIAS magnet.

    Based on my experience, if this magnet is removed, you will still get a current induced in the coil when the rotor is spinning. My hypothesis is that with the magnet in place, ( you know have a magnetic field in the center of the coil) you will get a larger signal.

    Personally, I am wondering more the signal processing circuitry and the software in the ECU as to what it takes to avoid a fault detection. If the software is comparing the differential signal between both coils, it may throw a fault because the difference in signals from each sensor may exceed a preset value in the Software. (this assumes what I read is correct and the broken magnet is 1/2 of the strength of the other magnet) If this is true, then I am assuming that the signal generated would be different in the coils perhaps in amplitude.

    another test would be that the signal from the individual sensor might be below some predetermined threshold.

    I have a 3rd bike I will be working on later, I may be inclined to run some experiments just to satisfy curiosity, LOL
    Pim will probably set up a test stand to explore all of the theories we have talked about and give you some really in depth answers. I always have to have him translate it to "Arkansas" so I can understand it.
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