4bt Tach / Rpm reference or crank sensor
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Thread: 4bt Tach / Rpm reference or crank sensor

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    Default 4bt Tach / Rpm reference or crank sensor

    Anybody have any CHEAP ideas to get an rpm/tach reference for tach and stand alone trans controller? I was thinking crank trigger wheel..cut with a water jet (or bought on ebay) and magnet sensor from MSD.. any ideas? Alternator signal? Anything I'm overlooking? I saw that there is an available crank sensor for 4bt's for marine apps but can't find any part numbers! Chris

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    Almost every possible way to run a tach can be found with this site's search engine, a whole bunch of threads about that. Check with tach, tachometer, pickup etc. and you should find what you're looking for.

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    1995 12v out of a dodge will have a harmonic balancer with 2 slits in it and a sensor mounted to the front timing cover. I am picking one up on Sunday but i haven't figure out how i'm going to use it yet.

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    Quote Originally Posted by Diesel Durango View Post
    1995 12v out of a dodge will have a harmonic balancer with 2 slits in it and a sensor mounted to the front timing cover. I am picking one up on Sunday but i haven't figure out how i'm going to use it yet.
    I planned to use the same balancer setup with the hall effect pickup. Then I realized I put my belt tensioner too close. I don't know what to do now.
    Does anyone have the outside diamater of the Dodge 6bt balancer handy???
    I might be able to squeeze it in.

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    I think I figured it out..

    http://www.dakotadigital.com/index.c...rod/prd129.htm

    Looks like I could just drill and tap a hole and have this sensor count the flywheel teeth.

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    Quote Originally Posted by torquenturbo View Post
    I think I figured it out..

    http://www.dakotadigital.com/index.c...rod/prd129.htm

    Looks like I could just drill and tap a hole and have this sensor count the flywheel teeth.
    Your link didn't work for me...
    The GM adapters have a hole on the drivers side that is lined up with the teeth. I don't know if the Ford or Dodge units have it??

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    how about :

    http://store.summitracing.com/partde...0&autoview=sku

    same thing.. but at summit. I think its meant to be facing perpendicular to the teeth and not from the side (like the hole your talking about) {I think?}

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    vdo also do some hall effect and reluctor type screw in sensors. does anyone know what the thread is in the adaptor ? you may be able to screw one of these straight in.
    It pulls like a 14 year old with a playboy !

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    Advance adapters has an idea with the 4.2L/4.0L stroker builds/transmission swaps. Machine the CKP sensor triggers into the front harmonic balancer. Not alot of meat on the 4bt pulley to do this, but maybe weld a ring on and true it up on a lathe?

    http://blog.hemmings.com/index.php/2...-step-forward/

    These are the timing marks for a 6cyl, 4 pulses x 120... 4Cyl (like my TJ was) has 4 marks at 180. Haven't gotten into the specific spacing or clocking on it yet, but I'm going to end up doing something like this, so I can use the stock CKP and the factory tach.
    Last edited by fitty; 11-30-2007 at 07:43 PM.
    2000 Jeep TJ. 4BT, NV4500, NP231, D30/D35, 5.5" Longarm, 35" MTR's, 3.73 gears.

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    Quote Originally Posted by torquenturbo View Post
    I think I figured it out..
    Looks like I could just drill and tap a hole and have this sensor count the flywheel teeth.

    I have that one. There is already the correct hole on the pass side, right above the starter, for the sender on my Ford block adapter. Right size hole and thread pitch, even. I the flywheel I have has 146 teeth.
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    ISS Pro has several setups.....universal and engine specific. Easiest way to find stuff is to download their catalog.

    http://www.isspro.com

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    Lately I've been stuck doing other things.. BUT I wanted to let everybody know what I was up to..making a crank trigger wheel.

    Last pics in my yahoo set at
    http://4btswaps.com/forum/showthread.php?t=1894

    I had a .250 thick aluminum plate spun on a lathe to 8" (just bigger then crank pulley) I'm going to thread 4 bolts into it (4 because the HEI dist. gave out 8 pulses fer revolution).

    The spacer was made out of aluminum as well.. (3.5" x 1") (5/8" or 16mm center hole)

    The magnetic sensor (VR) was found on Ebay for $20 (originally from a Onan/cummins generator governor). Sensor will be wired to an HEI module on a heatsink mounted somewhere in the engine bay. The reason for this is the magnetic variable reluctance sensor (as well as the HEI pick coil) put out an AC sine wave and the factory TBI ecm is looking for a DC square wave...the HEI module does this for us.

    basically this will let me use my factory tach AND tell the TCI trans controller what RPM the engine is at to control the 4l60E.

    Next up..TPS and fabbing a bracket for it.
    93 FS Blazer 4bt/4l60e/np241

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    Quote Originally Posted by torquenturbo View Post
    I had a .250 thick aluminum plate spun on a lathe to 8" (just bigger then crank pulley) .... The magnetic sensor (VR) was found on Ebay for $20 (originally from a Onan/cummins generator governor).
    Sorry, but it won't work. Magnetic sensors won't sense an aluminum wheel, since magnets are not attracted to aluminum.
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    The way I see it he'll be fine, the sensor will read the bolt heads.

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    Quote Originally Posted by averagef250 View Post
    The way I see it he'll be fine, the sensor will read the bolt heads.
    Only if it is within a certain distance of them.
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    Correct.. I'm drilling and tapping the outer edge side of the disc..
    Here are some pics before final touches!
    11-14-07_1757.jpg

    12-04-07_1950.jpg
    93 FS Blazer 4bt/4l60e/np241

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    You could mark every 90*, drill a 1/8" hole very close to the edge and epoxy in small pieces of 1/8" steel rod for the magnet to sense.
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    how about thread the holes and insert setscrews?
    2000 Jeep TJ. 4BT, NV4500, NP231, D30/D35, 5.5" Longarm, 35" MTR's, 3.73 gears.

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    Quote Originally Posted by fitty View Post
    how about thread the holes and insert setscrews?
    That works, too. Just make sure to epoxy them so they don't vibrate loose.
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    Well did it work?? I am curious to find out.

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    It WILL work I've been suffering the last couple of days from a sinus infection (possibly caused by sandblasting rusty sh*t!!! + crappy resirator) and haven't gotten the chance to get back to it.

    see:

    http://members.aol.com/pullingtractor/ignition.htm

    3/4's the way down that web page should explain everything..

    basically the reluctor (weather it be in your distributor or next to a trigger wheel) puts off AC pulses.. the GM ecm..or in my case TCI trans controller is looking for square wave DC signal. Converting it is the basic job of the HEI ignition module. Make sure to mount it to a heat sink and up high and dry!

    From what I've been reading (not proven by me yet!!) the HEI module is tripped by the AC sine wave crossing the zero point...and the frequency of - to determine RPM.

    I put the HEI distributor on a scope at work and my VR sensor.. the HEI puts out up to 6 volts AC and my sensor puts out 2 volts AC. The electronic gurus at work seem to think that won't even matter. That is yet to be determined. Any General Motors / Delphi / Siemens guys in the house??????
    93 FS Blazer 4bt/4l60e/np241

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    Quote Originally Posted by torquenturbo View Post
    It WILL work

    http://members.aol.com/pullingtractor/ignition.htm

    3/4's the way down that web page should explain everything..

    basically the reluctor (weather it be in your distributor or next to a trigger wheel) puts off AC pulses.. ................. the HEI module is tripped by the AC sine wave crossing the zero point...

    I read that page....I see nothing that says the trigger wheel can be aluminum and still work. The sensor needs to read from a notched steel wheel, or something steel (like the rods pieces/ set screws we talked about)

    The only way you will generate an AC signal is if the magnet in the pick-up senses something ferrous passing by. Aluminum isn't ferrous.
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    Just how wide or narrow can the notches be? I have a couple ideas. One is to use the large holes already in the crank pulley, and mount the sensor in front of the pulley to read them. The other thing I was thinking about to have an easy way to get a certain number of teeth, and have them run true, is to use a motorcycle chain sprocket. Rear sprockets can be had in many diameters and tooth numbers. By grinding away teeth, the empty space can be widened, and exact tooth count can be adjusted. I'm thinking about this for my project. I need to check my old flexplate to see the number of holes in it, then get a sprocket to match.

    Most sprockets are up in the high 30's to low 50's for tooth count. Lets say my flexplate has 15 notches. I just have to get a 45 tooth sprocket and grind off 2/3 of the teeth (grind off pairs, leaving one tooth between). If I have 20 notches, grind off every other tooth of a 40 tooth sprocket.

    Will an original equipment crank sensor pick up something as small as the tooth of a sprocket?

    Jim
    Milan, New Hampshire
    2000 Durango 4bt/NV4500 project
    4bt Durango Photo Album

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    As long as you are using steel parts inserted into the aluminum plate, I think it will work. I have done this on a similar project but I put the bolts into a cast iron flywheel. It worked fine that way.
    I used anearly Mopar ignition module for an earlier project. They are about 5" x 4" x 1". Typically, they were mounted on the firewall or inner fender. They can be triggered easily using a hall effect pickup like the one you are talking about. These modules can be had a the salvage yards for cheap. I constructed a hall effect pickup and mounted it on an old lawn tractor engine. I used that to fire the Mopar ignition module. The hall effect pickup was adjustable to set my timing. It worked fine. For a tach sensor, you would need 2, 3, or 4 bolts on the crank depending if the tach was setup for 4, 6 or 8 cyl. Remember gassers fire every other revolution. I used steel 10-24 allen head cap screws on my setup. The hall effect pickup has to be VERY close. I think I used cardboard from a cereal box as a feeler gauge.
    If there is a surplus electronics store in you area, you may find hall effect parts there. My pickup was the size of a tiny transistor. I think it cost about $1.50. That was epoxied on a mounting bracket.
    I think I have that old ignition system in a drawer in the garage. (The lawn tractor is long gone) I'll have to dig it out.

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    The Mopar ignition box is a good idea. I wonder if you could use it as a stand alone tach driver. Just use a big ceramic resistor in place of the ignition coil.

    You could even gut out an old Mopar distributor for the pick-up.

    Feeler gauge sets have brass feelers for setting the gap on those old mopar systems. You are right, the pick up must be CLOSE!
    1979 F-250 4WD, NP435 trans, NP205 TX case, 3.54 gears. IP turned up, H1C from 1993 12V with 12cm housing, 3" in and out FMIC.

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    Hmmmm, now I'm wondering if the newer Dodges use the crank sensor or the distributor to read engine RPMs to the PCM. For the newer gauge clusters, there isn't a separate circuit to tap into for the tach. There is a BUS circuit that runs the whole gauge cluster from the PCM. I'm keeping the PCM (as many others are doing) to run my gauges, so now I have to find out how the PCM reads engine RPMs.

    Lots of ideas and info on here!

    Jim
    Milan, New Hampshire
    2000 Durango 4bt/NV4500 project
    4bt Durango Photo Album

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    Quote Originally Posted by nhdiesel View Post
    Hmmmm, now I'm wondering if the newer Dodges use the crank sensor or the distributor to read engine RPMs to the PCM. For the newer gauge clusters, there isn't a separate circuit to tap into for the tach. There is a BUS circuit that runs the whole gauge cluster from the PCM. I'm keeping the PCM (as many others are doing) to run my gauges, so now I have to find out how the PCM reads engine RPMs.

    Lots of ideas and info on here!

    Jim
    factory service manual says that it uses the CPS to trigger the tach.

    I still haven't done anything with mine, waiting on some money to get the dakota digital tach signal converter.

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    PCM gets the input from the "engine speed sensor" aka. Crankshaft Position Sensor. The Camshaft Position sensor is used in conjunction with the Crank sensor to determine fuel and spark delivery.

    To put my idea into play, cut the crankshaft position trigger marks into the harmonic balancer, instead of on the flywheel. If you match the marks that are on the gas flywheel, you'll get the same signal and the computer is none the wiser. You have to mount the crank sensor onto the front of the engine though.

    You could also play around with the timing marks. 4cyl would have 4 marks every 180°. 1000 rpm on the engine shows 1000 rpm on the tach. Like stock.

    6cyl has 4 marks every 120°. Using the 6cyl notches with a 4cyl computer would give you 1.5x the reading, or 1.5x the needle sweep, which is pretty close to what the difference is between a gas dodge tach and a diesel dodge tach. Hard to find a 4cyl dodge ram though.... Jeep on the other hand...
    2000 Jeep TJ. 4BT, NV4500, NP231, D30/D35, 5.5" Longarm, 35" MTR's, 3.73 gears.

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    I was looking at the aftermarket tachs for the 8 cyl gas motors. These all come in 8 or 10 k versions. I thought I may go to 2X for the tach reading. Instead of X 100 on the gauge it would be X 50. At 5000 on the gauge you would actually be at 2500 rpm. If you really want to impress the passanger go to 3X reading. @ 2500 you would read 7500 rpm. Doing this would increase the sensitivity of the gauge so you could get a more accurate reading. Instead of reading the 50 rpm difference between the 750 or 800 rpm at idle, you would read the 150 rpm difference between 2250 or 2400 with a 3X reading. Your multiplication factor would be limited by your expected motor rpm and the range of the tach.
    Rescaling the face would be a better option. Then there wouldn't be any conversion to the right rpm needed then. I just can't paint as well as they print the faces, of course my truck is a rat rod anyway.

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    "The PCM continually monitors the crankshaft position sensor to determine the engine speed, then sends the proper engine speed messages to the instrument cluster."

    straight from the 2001 durango FSM.

    cutting the same number of teeth as a flywheel into a harmonic balancer sounds like a nightmare.

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