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Doubled speed / odometer reading after rotor bolt replacement

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by KenOathcarn, Mar 7, 2015.

  1. The front rotor on my 2009 SM610 was cooked so I took it to a shop to have it machined today. The guy didn't have access to a heat source and destroyed the heads of the four rotor mounting bolts trying to get them out. We ended up having to drill them to get it off and machine it. Luckily, the threads in the hub didn't get damaged in the process and we were able to mount the disc back up with four matching M8 bolts he had at the workshop.

    When I got back on the bike the speedo / odometer were reading almost exactly double what they should have (~120km/h at 60km/h, ~200km/h at 100km/h etc.). When I got home I inspected it thoroughly and couldn't see anything wrong. The manual specifies ~2-4mm for the gap between the magnet and sensor and this was correct. The only thing that's changed is the rotor mounting bolts.

    I used a spanner to check of the bolts were magnetic and it stuck to the magnet firmly, but not any of the new bolts. Then, I took the magnet off the rotor completely and took it for a ride and it's still reading double without it on.

    I disconnected the battery for 30 seconds to reset the dash (I had the speedo fail and start reading 0km/h at one point and that resolved it - known issue with Husky dash), but it didn't change anything.

    Can any of you guys think of anything else to check, or do I just need to get some OEM bolts and try swapping them back over?
  2. Does your manual say anything about damaging the sensor if it is exposed to a powerful magnetic force like from an electric drill?

    The work shop manuals from a couple my bikes warn about this and even things like magnetic pickup tools.

    I would assume the wheel was off and away from the sensor when the bolts were drilled though.

    Is the sensor fouled with iron fillings or anything?
  3. Nah, both the wheel and area around the sensor is good and clean from filings and dust. The wheel came off the bike without any issues and the drilling happened well away from the sensor, although the magnet was still on the disc. As I mentioned, the speedo was still getting a (dodgy, super high) reading even without the magnet on, although I'm not sure if this is normal or not.

    I think first step is getting a new set of OEM bolts. I'd really like a set of titanium Pro Bolt's, but don't want to tempt fate if they're the likely suspect...
  4. Are you sure none of the new bolts are at all magnetic. They might not need to be as strong as the proper magnet to cause trouble.
  5. Sounds like a bunch of cowboys, but lets leave that alone for now.

    Seems likely that you have a sensor issue, or the dash itself. Is the the electrical connection between the two intact, nothing disconnected, no broken wires etc?

    I think it unlikely that a bit of random magnetism in the bolts would be strong enough to trigger the sensor without it being plainly obvious with the spanner check you say you did. However you could check this by taking out all the bolts except the magnetic one, and take the bike for a spin around the block. Obviously you would have to refrain from using the front brake!

    If it is the bolts, then replacing them with titanium would certainly cure it, titanium = effectively non-magnetic.

    Good luck.
  6.  Top
  7. I finally got this resolved today - here's the story from start to finish...


    A few weeks back I ordered a new set of Galfer wave rotors from the US via Amazon for ~ AUD$500 shipped. Shipping took a while so I got to thinking about just getting the work done locally and was recommended a machine shop who quoted $90 to to machine the front disk. Awesome. The guy says come down on Saturday morning and we'll pull the wheel at his workshop.

    So I call up a hard parts store on Friday arvo and ask them for a brake pad price and availability;

    Me: "Do you have these really specific pads for this really specific, rare as hens teeth bike with a really specific caliper setup?"
    Them: "Yes. $40."
    Me: "Are you sure?"
    Them: "Yes. We keep them all in stock."
    Me: "You're really sure? You've got DP Brakes SDP638 in your hand right now?"
    Them: "Yes. $40. Coupla days mate. Beauuuutiful."

    Come Saturday morning I've still got the feeling they were more interested in getting me off the phone than anything else so I call back before I drive down there... "Sorry mate, that's a really specific pad that's basically only used on that bike and we don't stock it." No f...g shit. Thanks for clearing that up.

    I called about 6 other stores and managed to track a new set of pads down and head down to the machine shop. The bolt stripping / drilling nightmare described in my first post ensues. I get back on the bike and the speedo is cactus. By this time it's ~ 1600 Saturday and there's not much I can do.

    On Sunday my car throws the air-conditioning belt and I arrange to take it to a mechanic on Tuesday morning.

    On Tuesday morning I got up early and took to the remainder of the belt with a stanley knife so I could drive the car. I went straight down to Pro Bolt and pick up the only set of M8's they've got in stock that will fit the rotor. They were still a lot bigger than the standard bolts so I wasn't entirely surprised when the speedo still told me I was doing 160+km/h down my driveway.

    I called First Class motorcycles up at Lillydale, who happened to have 3 x silver and 1 x gold bolt in stock to fit the rotor. They express post them down and I put them on Thursday night. The speedo still thinks my driveway is some sort of epic salt flat run.

    By this time I'm thinking maybe the speedo sensor wire is cactus so I pull it out and do all the diagnostics I can think of. Cable tying it up on the fork leg wasn't getting a reading, but down by the caliper it was haywire. Everything is pointing to magnetism in the disc but I can't detect any with a spanner etc. still.

    I rode it up to First Class this morning and they put a couple of metal filings on the rotor and sure enough the f..kers stuck there. The process of machining the rotor had magnetised it. I couldn't f..king believe it.

    So, I tried to call the machine shop a couple of times and didn't get an answer so I rode past on the way home and they were there. I pull up and explain what's been happening and the guy goes "Oh, no problems, we'll put it on the demagnetiser." (apparently it's a thing.) and pulled the caliper, wheel, rotor again, put the rotor on the machine, flicked a switch and handed it back to me.

    We put it back on the bike and sure enough the speedo was spot on again. A week long, hair pulling pain in my balls ultimately resolved in about 4 seconds.

    • Like Like x 1
  8. Interesting, a new one on me but with Hall effect speed sensors they would be susceptible to stray magnetism. Well diagnosed..
  9. Well done. Pity they didn't think to do the demagnetising at the time, but live and learn. I hope the rotor bolts didn't get munted a second time!
    Did you give the rotor bolts a dose of Locktite on reassembly? They're supposed to have it.
  10. Nah... I'd put the bolts in and out about 5 times by that point and wasn't sure if they would have to come out again. I haven't pulled them and Loctite'd them since, but they're torqued to the moon so I'm not worried about it.

    Just saw you ride a CRF... is it plated / tarded?
  11. Yes and yes. I get some funny looks when I roll up to join a group ride of GSXR600's+ and CBR's etc!

    If it was me, I'd be Loctiting those bolts. Some people maintain they are single use only, with the threadlocker I'd be happy enough. Only take a few minutes for peace of mind, the consequences could be ugly.