6 cyl. tach in v8 conversion
Discussion
catfishdb said:
I have the original Jaeger 6 cyl. tach in my 2500m. The engine is now a 302 Ford unit. Is there a way to keep the original tach but have it read the v8 rpms correctly?
Thanks,
Arthur
Yes send it to Alan and he will convert and at the same time refurbish he has done mine on the Tuscan not fitted yet but I believe a simple conversion if you know what your doingThanks,
Arthur
http://www.thegaugeshop.com/
Sorry just realised your in another World LOL sorry but if you search over there you may find someone in Canada if not just send it here
Andrew
Edited by prideaux on Monday 21st April 15:51
Actually, if it's a Lucas built tacho,which I think Jeager ones are, most of the older types have an adjuster on the circuit board inside, and it has enough range for 4,6, or 8 cyl blocks.
You need to borrow a tach to compare it with, or wire it to a car with a tacho, to make sure you adjust it right.....
You need to borrow a tach to compare it with, or wire it to a car with a tacho, to make sure you adjust it right.....
Thanks guys,
If Bernard had not come up with the info about Nisonger Instruments I might have tried to ship it back to England. Thanks anyway Andrew.
I will have a look at the tach when I get the car back this weekend Andy but I wonder if this is the case with mine. It is labelled on the face 6 cyl.
I will give Nisonger Instruments a call in the morning to see what they might be able to do Bernard.
When I blip the throttle to down shift the needle swings around quickly to 7-8000 rpm. It is getting interference of some kind I believe. With the idle set at 750-800 rpm the tach shows roughly 1200 to 1400 rpm.
Just to be safe I have a rev limiter set at 5000rpm. I have not hit it yet. The noise at present is immense.
Arthur
If Bernard had not come up with the info about Nisonger Instruments I might have tried to ship it back to England. Thanks anyway Andrew.
I will have a look at the tach when I get the car back this weekend Andy but I wonder if this is the case with mine. It is labelled on the face 6 cyl.
I will give Nisonger Instruments a call in the morning to see what they might be able to do Bernard.
When I blip the throttle to down shift the needle swings around quickly to 7-8000 rpm. It is getting interference of some kind I believe. With the idle set at 750-800 rpm the tach shows roughly 1200 to 1400 rpm.
Just to be safe I have a rev limiter set at 5000rpm. I have not hit it yet. The noise at present is immense.
Arthur
catfishdb said:
I have the original Jaeger 6 cyl. tach in my 2500m. The engine is now a 302 Ford unit. Is there a way to keep the original tach but have it read the v8 rpms correctly?
Thanks,
Arthur
Hi ArthurThanks,
Arthur
This little converter, or similar product will do the trick for you, without rebuilding the internals of your original tacho
http://www.ebay.com/itm/DAKOTA-DIGITAL-UNIVERSAL-T...
http://www.ebay.co.uk/itm/TACH-ADAPT-Digital-Tach-...
madsvlund said:
Hi Arthur
This little converter, or similar product will do the trick for you, without rebuilding the internals of your original tacho
http://www.ebay.com/itm/DAKOTA-DIGITAL-UNIVERSAL-T...
http://www.ebay.co.uk/itm/TACH-ADAPT-Digital-Tach-...
Mads thats interestingThis little converter, or similar product will do the trick for you, without rebuilding the internals of your original tacho
http://www.ebay.com/itm/DAKOTA-DIGITAL-UNIVERSAL-T...
http://www.ebay.co.uk/itm/TACH-ADAPT-Digital-Tach-...
No cheaper though than doing it right i think Alan charged me a little more but had the whole guage refurbished and cleaned ready for re fitting at the same time came back like new plus it means another thing to go wrong IMOP
A
I love this forum. So many options for what I figured might be possible but was not certain. I am going to get this sorted and will report back.
Looks like this weekend might be clear of rain so no hope of working on the car other than driving it. New tires being fitted as we speak.
Thanks everyone,
Arthur
Looks like this weekend might be clear of rain so no hope of working on the car other than driving it. New tires being fitted as we speak.
Thanks everyone,
Arthur
What I do know about older tachos, from Ford, Lucas,Triumph etc. in UK - in case it helps.
The really old tachos (1960's) used a current loop, they have a wire loop on the back which sits in series with the coil. They have a very simple circuit with a single transistor, and DO have an adjuster for the number of cylinders.
Later ones (like 1970's) went to voltage trigger, with an early type IC (8 pin), some of these had adjusters, some had a 'calibration resistor' which sits above the circuit board to identify it.
Some other types (BMW) need a high voltage pulse to work, but Lucas ones seem happy with 12 volt trigger pulses
The actual gauge/needle is a simple magnet/coil, very like a voltmeter. There are a few extra components to smooth out the reading, and to filter out noise to get a reliable stable reading.
All of the tachos are a 'voltage pump', a kind of monostable circuit, which simply generates a fixed width pulse from a 'trigger'pulse. As the tigger pulses get closer together, the average output gets higher, as the fixed width pulses get closer together.
It's not rocket science to calibrate them, just think about the number of pulses per second. At 1000rpm, a 4 cylinder engine generates 2000 pulses per minute (2 sparks per revolution), or 33 pulses per second. A 6 cyl engine develops
3000 pulses or 50 pulses per second, which just happens to be the same as household electricity cycles (50 hertz) in UK, so it's not hard to rig up a little transformer to generate a 50 hertz pulse stream at 12 volts. An 8 cyl engine develops 66 pulses second. I think household electricity in US is 60 hertz, which would be 1200rpm for a 6 cyl engine, and 900 for an 8. Not sure what Canada has.
Or another way is that a 6 cyl tacho should read 33% too high on an 8 cyl engine.
The older tachos actually read if you wire them wrong way round, but read FAR too high (That is, wiring the 12v to the pulse input, and pulse input to the 12v). So check this if you reckon your tacho reads much,much too high, as it's not at all obvious on some of the tachos, and they ain't labelled.
Also, several of the older types don't read properly with an electronic ignition module, so if you're 302 has an electronic module, it may confuse the tacho.
If you really want to keep the tacho, it's possible to replace the innards for a more modern circuit which WILL work with later ignition systems, but you will need a specialist for this option, unless you're an electronics engineer !
The really old tachos (1960's) used a current loop, they have a wire loop on the back which sits in series with the coil. They have a very simple circuit with a single transistor, and DO have an adjuster for the number of cylinders.
Later ones (like 1970's) went to voltage trigger, with an early type IC (8 pin), some of these had adjusters, some had a 'calibration resistor' which sits above the circuit board to identify it.
Some other types (BMW) need a high voltage pulse to work, but Lucas ones seem happy with 12 volt trigger pulses
The actual gauge/needle is a simple magnet/coil, very like a voltmeter. There are a few extra components to smooth out the reading, and to filter out noise to get a reliable stable reading.
All of the tachos are a 'voltage pump', a kind of monostable circuit, which simply generates a fixed width pulse from a 'trigger'pulse. As the tigger pulses get closer together, the average output gets higher, as the fixed width pulses get closer together.
It's not rocket science to calibrate them, just think about the number of pulses per second. At 1000rpm, a 4 cylinder engine generates 2000 pulses per minute (2 sparks per revolution), or 33 pulses per second. A 6 cyl engine develops
3000 pulses or 50 pulses per second, which just happens to be the same as household electricity cycles (50 hertz) in UK, so it's not hard to rig up a little transformer to generate a 50 hertz pulse stream at 12 volts. An 8 cyl engine develops 66 pulses second. I think household electricity in US is 60 hertz, which would be 1200rpm for a 6 cyl engine, and 900 for an 8. Not sure what Canada has.
Or another way is that a 6 cyl tacho should read 33% too high on an 8 cyl engine.
The older tachos actually read if you wire them wrong way round, but read FAR too high (That is, wiring the 12v to the pulse input, and pulse input to the 12v). So check this if you reckon your tacho reads much,much too high, as it's not at all obvious on some of the tachos, and they ain't labelled.
Also, several of the older types don't read properly with an electronic ignition module, so if you're 302 has an electronic module, it may confuse the tacho.
If you really want to keep the tacho, it's possible to replace the innards for a more modern circuit which WILL work with later ignition systems, but you will need a specialist for this option, unless you're an electronics engineer !
Edited by RCK974X on Wednesday 23 April 21:30
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