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Old 18th November 2012, 02:12   #46
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by ilangop View Post
1)..........the idea to use a Motor cycle tachometer for a car. One fine day I even bought a tacho from a spare part shop. He charged me Rs 450/- for this.

2)........ From the data sheet I could locate where exactly to hit, to make the required calibration

3)....In the motorcyle, the tacho displays the rate at which spark occurs, and the same principle is going to be used here. But the problem here is that in a bike the tacho would sense one spark per crank revolution. .........

4)The circuit board after replacement with the appropriate components (a blue coloured preset and a 220K resistor) are also shown in the picture below. .....

okay first of all let me say i am a fan. Amoung all the people i know about on this forum, you along with behram dhabhar sir i believe have the most technically knowledge. and your DIY attitude is just inspiring. If more engineers in our country were like you and actually loved doing what they do then , we indians would actually be creating our own technology and not keep importing it. maybe if the future generations are more like you , we can stop importing jets from russia and actually make our own. Maybe tata and mahindra will design their own engines without needing help from mercedez, renault or AVL.

Okay here are my questions

1.You say you got a tacho from a spare parts shop. was this part second hand? cuz AFAIK there are no spare parts guys selling bike tachos seperately.

2. this data sheet you mentioned is of the IC that was installed in the tacho?
you were able to figure out the whole working of the tacho from this data sheet ? And also the mods required? i am guessing your area of specialisation is electronics?

3. you say there is one spark per crank revolution in a bike. I am very confused by this. it takes 2 CRANK(not cam) revolutions to complete a 4 stroke cycle and there is only one spark per cycle , so shouldnt there be one spark for every 2 rotations?

4.If i need to go and buy this preset then i just go and tell the guy i want one or are their any specifications to mention?
and the resistor, is it specific to the no of cylinders? what if i want to use it on a 3 cylinder engine? can you help me with calculations? or just point me to the part of the datasheet that is useful to decide the change in resistance

and thank you for sharing your knowledge with us all.And keep DIY-ing. i think i can learn a lot from you.
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Old 19th November 2012, 10:30   #47
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Default Re: DIY tacho for a car, using a bike's tacho

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1.You say you got a tacho from a spare parts shop. was this part second hand? cuz AFAIK there are no spare parts guys selling bike tachos seperately.
It is a new tacho. You can ofcourse grab them from the Pulsar 150 UG1 where the tacho and Speedo are in separate boxes. You can even try one from Thunderbird, but it might be expensive.
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2. this data sheet you mentioned is of the IC that was installed in the tacho?you were able to figure out the whole working of the tacho from this data sheet ? And also the mods required?
Yes, the data sheet has sufficient information for you to alter the calibration.
"i am guessing your area of specialisation is electronics?" - Not really. It is only the interest for DIY that drives you to somehow understand the stuff. Dont we see lot many doctors and software engineers discussing cars in this forum.
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3. you say there is one spark per crank revolution in a bike. I am very confused by this. it takes 2 CRANK(not cam) revolutions to complete a 4 stroke cycle and there is only one spark per cycle , so shouldnt there be one spark for every 2 rotations?
In principle your statement holds good for cars which had a distributor to divert the spark to the appropriate cylinder. But there is something called the "Wasted spark method", where the cylinders are fired on every TDC. This idea is followed in almost every modern car like the Hyundai Accent/santro, Tata Indica/Nano, etc. In motorcycles, the cdi unit receives one trigger per revolution of crankshaft (not camshaft).
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4.If i need to go and buy this preset then i just go and tell the guy i want one or are their any specifications to mention?
and the resistor, is it specific to the no of cylinders? what if i want to use it on a 3 cylinder engine? can you help me with calculations? or just point me to the part of the datasheet that is useful to decide the change in resistance
Check the pdf attached with this post (post no:27 in this thread)
http://www.team-bhp.com/forum/techni...ml#post1650763
Hope this helps, else post the picture of the dial you will be using and I can detail you the calculation. All the best
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Old 7th December 2013, 23:01   #48
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Post Re: DIY tacho for a car, using a bike's tacho

Beautifully done. I am planning to install one in my motorcycle without a tachy. But though the mod of soldering the resistors and transformers seem quite easy, it's quite a pain in the posterior for a guy like me with no preset knowledge on electricals.

So can any other off the shelf tacho be easily swappable for a motorcycle or does the mod mod needs to be done for this too. Since the spark equation is almost similar for motorcycles. I just want to be clear.

Cheers!
VJ
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Old 8th December 2013, 19:13   #49
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by VijayAnand1 View Post
Beautifully done. I am planning to install one in my motorcycle without a tachy.
Hi Vijay, Which bike have you got? You can directly use any 2 wheeler tacho without any mod, because they all are triggered with 1 pulse per crank revolution.
-Ilango
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Old 9th December 2013, 16:54   #50
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Post Re: DIY tacho for a car, using a bike's tacho

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Hi Vijay, Which bike have you got? You can directly use any 2 wheeler tacho without any mod, because they all are triggered with 1 pulse per crank revolution.
-Ilango
I have the TVS Victor GLX 2007 ES one. Thank you so much, ilangop. . Any idea to ideally know the redline of a given engine w.r.t the tachy alone? Because since you've calibrated the tachy to stay at the 1.5 RPM. Forgive me for the noob query, just wanted to know can we estimate the redline or max RPM of a given engine beforehand installing the tachy? Any pointers would be highly appreciated.

Cheers!
VJ
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Old 10th December 2013, 06:47   #51
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Default Re: DIY tacho for a car, using a bike's tacho

[quote=VijayAnand1;3315315]I have the TVS Victor GLX 2007 ES one. Thank you so much, ilangop. . Any idea to ideally know the redline of a given engine w.r.t the tachy alone? Because since you've calibrated the tachy to stay at the 1.5 RPM. Forgive me for the noob query, just wanted to know can we estimate the redline or max RPM of a given engine beforehand installing the tachy? Any pointers would be highly appreciated.
QUOTE]

Hi Vijay,
Buy a tachometer of any 2 wheeler. 2 wheelers have a crank position sensor which generates 1 pulse per revolution, which is used to fire the spark plug through a TCI or CDI. This is called wasted spark method where there is 1 dead spark during the exhaust stroke also. This means in a test bench when you want to see the tacho work with a stepped down (12 to 15V) AC, at 50 Hz the meter should read 50 X 60 = 3000 rpm.
Similarly in a four cylinder engine there will be 4 sparks for 2 crank revolutions, hence you need to recalibrate the tacho to read 50 X 60 /2 = 1500 rpm. Hope this clears your doubt. I think you can directly use a Fiero instrument cluster, though not sure.
Knowing the redline of an engine and wiring a tacho of another bike in your Victor are just independent of each other. Just connect the +ve of tacho to key on, -ve to any body gound and the tacho input to the ign coil (+ or - depends on your CDI). Just try 1 after the other. All the best.
-Ilango
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Old 10th December 2013, 21:42   #52
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Post Re: DIY tacho for a car, using a bike's tacho

Thank you so much, Ilangop.

Cheers!
VJ
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Old 20th October 2015, 16:42   #53
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Default Re: DIY tacho for a car, using a bike's tacho

Hello Ilango, I'm planning to install a 4 stroke single cylinder tacho on a 2 stroke single cylinder bike (to be precise, a pulsar tacho on RX) Can you please help me on this modification?
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Old 21st October 2015, 09:18   #54
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Default Re: DIY tacho for a car, using a bike's tacho

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Hello Ilango, I'm planning to install a 4 stroke single cylinder tacho on a 2 stroke single cylinder bike (to be precise, a pulsar tacho on RX) Can you please help me on this modification?
No modification needed. Just connect the Tacho signal input to the Ignition coil input wire (not the wire to spark plug). All 4 stroke motor cycles (excluding the RE350 which ran on point & condenser) produce 1 spark per revolution. Hence no need to modify anything.
My suggestion would be to use a RXZ tacho box + dial with a Pulsar old model tacho's circuits. Can you post a picture of what you have in your mind.
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Old 21st October 2015, 10:35   #55
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by ilangop View Post
No modification needed. Just connect the Tacho signal input to the Ignition coil input wire (not the wire to spark plug). All 4 stroke motor cycles (excluding the RE350 which ran on point & condenser) produce 1 spark per revolution. Hence no need to modify anything.
My suggestion would be to use a RXZ tacho box + dial with a Pulsar old model tacho's circuits. Can you post a picture of what you have in your mind.
Interesting. Need to check it out.
Guys I talked to have always mentioned that 4 stroke tacho will always show twice the reading if installed on a 2 stroke bike.

Also, wondering if calibration will be required for difference between RXZ (up to 10K rpm) and Pulsar tacho (up to 12K rpm) dial?

Thanks.
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Old 21st October 2015, 10:51   #56
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by ilangop View Post
All 4 stroke motor cycles (excluding the RE350 which ran on point & condenser) produce 1 spark per revolution. Hence no need to modify anything.
Please correct me if I'm wrong. Single cylinder 4 stroke engine works with 1 spark for 2 revolutions. So using a 4s tacho on 2s will display double the actual figure.

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Originally Posted by ilangop View Post
My suggestion would be to use a RXZ tacho box + dial with a Pulsar old model tacho's circuits. Can you post a picture of what you have in your mind.
I have the same thought and I would like to have this modification without robbing the stock looks of an RX.

Last edited by Mr.Boss : 21st October 2015 at 10:52.
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Old 21st October 2015, 11:07   #57
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by Mr.Boss View Post
Single cylinder 4 stroke engine works with 1 spark for 2 revolutions. So using a 4s tacho on 2s will display double the actual figure.
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Originally Posted by ilangop View Post
In principle your statement holds good for cars which had a distributor to divert the spark to the appropriate cylinder. But there is something called the "Wasted spark method", where the cylinders are fired on every TDC.
See ilangop's explanation above - the wasted spark principle is used to remove the need for a distributor, since that adds complexity and is prone to failure particularly on exposed engines like motorcycles.

Without a distributor and by using a wasted spark design, you can directly trigger the spark from the crankshaft every time the piston reaches TDC (or slightly in advance, as the case may be). In a 4-stroke, this will occur once at the end of the compression stroke (i.e. this is the useful spark) and once at the end of the exhaust stroke (i.e. the wasted spark).

Its an elegant concept to improve simplicity. It also means that for every crankshaft rotation, a spark is triggered, irrespective of whether the engine is a 2 stroke or 4 stroke.

Read more: https://en.wikipedia.org/wiki/Wasted_spark (particularly the section on single-cylinder use).

Last edited by arunphilip : 21st October 2015 at 11:12.
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Old 21st October 2015, 11:33   #58
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by Mr.Boss View Post
Hello Ilango, I'm planning to install a 4 stroke single cylinder tacho on a 2 stroke single cylinder bike (to be precise, a pulsar tacho on RX) Can you please help me on this modification?
Quote:
Originally Posted by ilangop View Post
No modification needed. Just connect the Tacho signal input to the Ignition coil input wire (not the wire to spark plug).
Correct. Just connect the blue wire from the tacho (other two wires are +12V and ground)

I'm using a pulsar tacho on my RX since 2004. It shows double the value with the stock CDI. If you use a RDD CDI it will show the right value. I made a video of it back in early 2007



A month later, ditched the stock pulsar cases for much better looking RD350 cups.

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Last edited by SunnyBoi : 21st October 2015 at 11:35.
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Old 21st October 2015, 13:32   #59
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Default Re: DIY tacho for a car, using a bike's tacho

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Originally Posted by vaasu View Post
Interesting. Need to check it out.
Guys I talked to have always mentioned that 4 stroke tacho will always show twice the reading if installed on a 2 stroke bike.

Also, wondering if calibration will be required for difference between RXZ (up to 10K rpm) and Pulsar tacho (up to 12K rpm) dial?

Thanks.
Quote:
Originally Posted by Mr.Boss View Post
Please correct me if I'm wrong. Single cylinder 4 stroke engine works with 1 spark for 2 revolutions. So using a 4s tacho on 2s will display double the actual figure.

I have the same thought and I would like to have this modification without robbing the stock looks of an RX.
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Originally Posted by SunnyBoi View Post
Correct. Just connect the blue wire from the tacho (other two wires are +12V and ground)

I'm using a pulsar tacho on my RX since 2004. It shows double the value with the stock CDI. If you use a RDD CDI it will show the right value. I made a video of it back in early 2007
Please check post No 1 & 2 in this thread. The analog tachometer of Pulsar or Discover 150 is calibrated for 1 pulse per revolution. I have checked & confirmed it on the same post.

Calibration for RXZ dial:
You need a 12-0-12 500mA transformer to generate the rpm signal. Also you need 2 nos of 1N4007 diodes. Connect the diodes to make a rectifier. Hence you have 100Hz at the output, means 100 pulses per second. Ideally the needle should point at 100*60 = 6000 rpm.
After swapping the electronics & the gauge behind the RXZ you can feed the diode output to the tachometer and adjust the screw in the blue coloured potentiometer till the needle points 6000. Simple.
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Old 25th November 2016, 09:34   #60
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Default Re: DIY tacho for a car, using a bike's tacho

Hello,

Is it possible to mount a Ritzís tacho in a santro and get it to work? This is for my friendís car and we are not going to try any DIY here but wanted to go to the mechanic with some basic knowledge on how likely this will work.

My friend is specific about putting up the Ritz tacho and if not feasible we can look out for other tacho options.

Appreciating expert suggestions.

Cheers!
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