Inductive pickup to drive a tachometer..

[R.O.R-2.0]

ok, so i pirated a ford crank angle sensor off a ford ranger 4.0L engine, and its an inductive pickup, whenever metal passes by it, signal comes out..

in theory, i can hook this up to my gasser tach, with 2 nuts welded to the crank pulley 180* out, and have the tach work, correct? or do i need some sort of signal conditioner?

any help or tips is greatly appreciated..

[wdkingery]

Highly interested

[Toby]

You should not need anything but the sensor and 2 tits to drive it. It must be a magnetic sensor though. I.E. one with a magnet inside. Ground one leg of the coil and run the other to the tach lead. The only issue is getting enough output from the sensor. The one in the FAQs is a transmission sensor IIRC for driving speedos. 2 tits on the crank gives the correct number of pulses to make the tach read correctly. IIRC the gap on such inductive pickups should be around .060". That should not be too hard to achieve. Rather than welding nuts on the pulley, I may play with a bolt on trigger wheel made of 16 gauge sheet steel. It would be nice to have the sensor behind the pulley making the sensor brackets more rigid and out of the way for belt changes.

[ToddA1]

Rather than welding nuts on the pulley, I may play with a bolt on trigger wheel made of 16 gauge sheet steel. It would be nice to have the sensor behind the pulley making the sensor brackets more rigid and out of the way for belt changes.

That's not a bad idea....  I only have an alt/pump belt, but it would look cleaner, sandwiched between the t/b sprocket and crank pulley.  I bought that Ford sensor months ago, I just need time to do it.

-Todd

[R.O.R-2.0]

You should not need anything but the sensor and 2 tits to drive it. It must be a magnetic sensor though. I.E. one with a magnet inside. Ground one leg of the coil and run the other to the tach lead. The only issue is getting enough output from the sensor. The one in the FAQs is a transmission sensor IIRC for driving speedos. 2 tits on the crank gives the correct number of pulses to make the tach read correctly. IIRC the gap on such inductive pickups should be around .060". That should not be too hard to achieve. Rather than welding nuts on the pulley, I may play with a bolt on trigger wheel made of 16 gauge sheet steel. It would be nice to have the sensor behind the pulley making the sensor brackets more rigid and out of the way for belt changes.

well, i welded 2 nuts to a spare crank pulley, 180* out from each other

and yes, my pickup is magnetic, it will stick to metal. it also produces a voltage anything metal passes by it.

i was going to run the signal to the green tach wire, and the ground to the tach ground. that should work right? then the tach will get the cleanest signal?

and yes, i was thinking about that, putting a trigger wheel on the BACK of the pulley, but there aint much room because the crank pulley basically sits on the lower timing cover..

you basically gotta go on the outside unless you wanna modify the timing cover.

and i would not sandwich the wheel between the sprocket and pulley. the pulley makes up the outter lip of the crank pulley, and if something else was in there between them, then it could rub the timing belt the wrong way..

[Toby]

Whatever is sandwiched between pulley and sprocket will do the same job as the side of the pulley, so the timing belt should not be an issue. Upon further consideration I think I will try TIGing a couple of tabs to the inside circumference of the pulley where they should not interfere with the cover. I need to lay my hands on a sensor to see if I will have enough room to fit it in under the water pump somewhere. I will pick the motor up in the air to get a good look at it in the AM.  I will have to play with it to see of 1/8" tabs have enough mass to reliably trigger the tach.

[R.O.R-2.0]

Whatever is sandwiched between pulley and sprocket will do the same job as the side of the pulley, so the timing belt should not be an issue. Upon further consideration I think I will try TIGing a couple of tabs to the inside circumference of the pulley where they should not interfere with the cover. I need to lay my hands on a sensor to see if I will have enough room to fit it in under the water pump somewhere. I will pick the motor up in the air to get a good look at it in the AM.  I will have to play with it to see of 1/8" tabs have enough mass to reliably trigger the tach.

there is about 1/16th of an inch between the timing cover, and the rear lip of the pulley.. i dont see it feasible to mount anything to the back side of the pulley..

so im going to have to take out 2 extra bolts when i take the belt off my car, big deal, i could care less, it adds maybe 1 extra minute to the removal and replacement of a belt.

[81 vw pu]

I've been thinking about this setup? I already have the mk2 gasser tach, but no W termial alternator.

http://www.ebay.com/itm/Dakota-Digital-Diesel-Flywheel-Tach-Unit-Adapter-DSL-2-/310153618523?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item483698a45b

[Toby]

I guess I was not being clear. I am talking about welding 1/8" nubs to the outside of the rim, not inside the pulley. If there is enough room for the sensor, that will make for much a stouter mount for the sensor.

BTW, does anybody know, off of the top their head how many tach nubs are visible through the timing hole. I know there is at least one, maybe 2. I will dig out a flywheel in the AM and look. If there are 2 we could set the sensor up in the timing hole plug. I am sure VW used them to drive some kind of tach at the factory during run in or testing.

Edit: I couldn't wait, so I rolled the GTI motor over and it has 2 tach nubs visible in the timing hole. The problem is that they are about 25* apart instead of 180* apart. If the tach drive counts the pulses this may be all that we need to drive the magnetic pickup. If on the other hand the tach drive electronics use some kind of temporal summation to produce a voltage I may be out of luck. I will give it a try once I get the GTI head back on.

[R.O.R-2.0]

I've been thinking about this setup? I already have the mk2 gasser tach, but no W termial alternator.

http://www.ebay.com/itm/Dakota-Digital-Diesel-Flywheel-Tach-Unit-Adapter-DSL-2-/310153618523?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item483698a45b

my setup is basically the same thing, minus the DSL-1.. i dont need one. my tach is natively accurate.

but it doesnt help that the sensor is already broken.. didnt even make it a mile before a chunk of gravel kicked up and ripped the face off the sensor..

but, i know it works. because my AUG turned 2800revs@55mph when it was in my jetta, and thats what my tach was reading.. and my idle was @ right about 950rpms.

another interesting fact:

the crank pulley i took off, was 6" across..

the one i put back on, was 4 7/8" across, and you can tell the difference. the engine revs a little easier, and boosts sooner.

[81 vw pu]

another interesting fact:

the crank pulley i took off, was 6" across..

the one i put back on, was 4 7/8" across, and you can tell the difference. the engine revs a little easier, and boosts sooner.

I do believe you just made your own underdrive!!!

[R.O.R-2.0]

another interesting fact:

the crank pulley i took off, was 6" across..

the one i put back on, was 4 7/8" across, and you can tell the difference. the engine revs a little easier, and boosts sooner.

I do believe you just made your own underdrive!!!

oh, i definitely did make an underdrive.. it was kinda necessary tho, because with the stock pullies, theres about 1/8th of an inch between the 2 pullies, and there wouldnt have been enough room for the nuts i welded to the outside lip of the crank pulley.

my 2 pullies were not the same offset tho, so i had to build a small spacer, and re-align the pullies, but everything works out, and the crank pulley still centers on the original crank pilot, so no hubcentric spacer was needed.

it takes more RPM to lite the alternator, and it seems to rev easier..

[R.O.R-2.0]

oh, i fixed my inductive pickup by the way. had to replace the magnet and fix the hole in the housing, but it all works again..

im such a cheap bastid.. but hey, who else do you know that has FIXED a destroyed inductive pickup?

[R.O.R-2.0]

car is sitting outside idling with a reading of 800rpms on my autometer sport-comp tachometer

and if you do this for your own car, then BE SURE TO BUILD THE BRACKET HELL FOR STOUT.. make sure it is not prone to vibration.

these engines get one hell of a vibration around 3000rpms, and my sensor bracket is apparently not stiff enough, and vibrates like mad around 3000 revs, allowing the face of the pickup to come into contact with the nuts on my pulley, and then bad things happen..

i will be stiffening up the bracket after class tonight, and will probably report back in the morning..

[ORCoaster]

Are we about to embark on another discussion of triangulation and proper welding techniques?  Gee I hope not.  And you are not cheap, the word is frugal.  Knowing the difference between the two is sheer genius by the way.  A great alternative here to the Tiny Tach I was thinking I needed.  Got pictures coming of the built hell for stout sensor and location?

frugal [ˈfruːgəl]
adj
1. practising economy; living without waste; thrifty
2. not costly; meagre
[from Latin frūgālis, from frūgī useful, temperate, from frux fruit]

cheap
   [cheep] Show IPA adjective, -er, -est, adverb, noun
adjective
stingy; miserly:at a low price; at small cost: