Wanted Honda 919 Km/h speedometer underlay - Wrist Twisters
 
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post #1 of 9 Old 04-10-2016, 12:02 PM Thread Starter
Tirone
 
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Wanted Honda 919 Km/h speedometer underlay

Maybe some of you have changed the speedometer underlay to show miles/h (something like his: HONDA CB900F2 F7 HORNET 2002-2007 REPLACEMENT MPH SPEEDO CLOCK DIAL UNDERLAY | eBay).

So in case you have now laying around the one that shows km/h I will be more than happy to buy it from you as I can't find it anywhere. Please PM me.

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post #2 of 9 Old 04-10-2016, 01:15 PM
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post #3 of 9 Old 04-10-2016, 03:18 PM
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You are better of finding another set of gauges rather than trying to remove the tach/speedo needles. I'm not sure anyone has ever had luck doing this since they will also need to be calibrated again if you actually do get them to come off. Which is also beyond most people's skill set and tool boxes.

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post #4 of 9 Old 04-11-2016, 06:10 AM
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Originally Posted by redline919 View Post
You are better of finding another set of gauges rather than trying to remove the tach/speedo needles. I'm not sure anyone has ever had luck doing this since they will also need to be calibrated again if you actually do get them to come off. Which is also beyond most people's skill set and tool boxes.
Is there a specified way to do it? If you could find out what the speedo output is encoded as and what frequency corresponds to what speed you could hook up an arbitrary signal generator and it would be pretty simple.

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post #5 of 9 Old 04-11-2016, 06:50 AM
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Originally Posted by badmoon692008 View Post

Is there a specified way to do it? If you could find out what the speedo output is encoded as and what frequency corresponds to what speed you could hook up an arbitrary signal generator and it would be pretty simple.
I wouldn't even know where to start. Your already ahead of most of us.

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post #6 of 9 Old 04-11-2016, 10:23 AM
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Originally Posted by badmoon692008 View Post
Is there a specified way to do it? If you could find out what the speedo output is encoded as and what frequency corresponds to what speed you could hook up an arbitrary signal generator and it would be pretty simple.
There is, but it's not public knowledge. Not for the faint of heart, or those new to electronics and signalling.

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post #7 of 9 Old 04-11-2016, 12:33 PM
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Originally Posted by badmoon692008 View Post
Is there a specified way to do it? If you could find out what the speedo output is encoded as and what frequency corresponds to what speed you could hook up an arbitrary signal generator and it would be pretty simple.
Let's figure it out.

First, you need the circumference of the rear tire in millimeters, usually calculated from the diameter times PI. Let's assume it's diameter is 630mm. That works out to 1979.2mm, and is the distance travelled when the rear wheel makes one revolution. From that the number of revolutions of the rear wheel per kilometer is calculated by dividing 1,000,000mm by the circumference: 505.253 revolutions of the rear wheel per kilometer. Take it out to as many decimal places as you can to eliminate stacking errors.

Second, multiply the final drive ratio (stock is {43 / 16} = 2.6875 : 1) by the number of teeth read by the speed sensor (countershaft 5th gear, 27 teeth) = 72.5625. That represents the number of pulses per revolution of the rear wheel.

Now the fun part: figuring out the frequency in Hz of the speedometer signal at a particular speed, arbitrarily 100 KPH. Let's see, 100 Km/H = 0.02777... kilometers per second, multiplied by the number of revolutions per Km (505.253), then multiplied by the pulse rate per revolution of the rear wheel (72.5625) = 1018.4 Hz. Since the VSS signal goes directly to the speedo, that should give an indication of close to 100 Km/H. Generally, a square wave form of 0 to 5 volts will produce an accurate reading from the speedo.

An advantage of setting the needle at 100 Km/H is at that speed it will read almost exactly right without the 15% or so error common to pretty much all 919 / Hornets I have ever heard of. Of course above and below that speed it will be off by a small percentage, but still considerably less error than stock.

There you go. Of course your numbers may be different due to the diameter of the rear tire and the final drive ratio if you have changed it from stock, or the EU final drive is different from the US.

One wrinkle: while the speedo may be accurate, the odometer is still reading in miles unless there is a way to switch it over to Km.

Rob

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post #8 of 9 Old 04-11-2016, 01:57 PM
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I'm not in front of my bike to look, but could it be possible to just slide the thing over the needle and set it in place ?? May have to widen the center hole a little, but is that an option ??

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post #9 of 9 Old 04-11-2016, 03:47 PM
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Originally Posted by hondatech9 View Post
I'm not in front of my bike to look, but could it be possible to just slide the thing over the needle and set it in place ?? May have to widen the center hole a little, but is that an option ??
I thought about this years ago...basically you'll have to break the existing plates or sand off the face otherwise light wont make it through.... New face would have to be split about 3mm so that you could slide it over the shaft for the needle. Now if you're okay with a giant hole in the new face plate I believe the hole would probably have to be at least1-2" to get the face plate over the needle without pulling the needle. Old face plate being in the way adds to the challenge as it's removing maneuvering space.

Keep in mind, I haven't seen the internals of the gauges in a couple of years now.

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