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General Information => FAQ/Tech Tips/Please Read First => Topic started by: R.O.R-2.0 on November 27, 2011, 12:00:52 am
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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..
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Highly interested
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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.
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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
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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..
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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.
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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.
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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
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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.
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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.
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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!!!
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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..
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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?
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car is sitting outside idling with a reading of 800rpms on my autometer sport-comp tachometer 8)
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..
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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:
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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 found that to work quite well.. I didn't even bother to try welding additional metal tabs to the pulley, just put a couple blobs of bubble gum on there, and ground them to look nice..
Kevin, if you can;t get your current sensor mounted sturdy enough, next trip to the junk yards look for one of the trans speed sensors as used in late model Fords. They are a little less bulky (easy to be broken) than the one from the 4.0.. I used one from a 4R70w out of a late 90's F-150.. It worked well enough that all I needed to do was bolt a piece of angle to the back of the block with a hole for the sensor to slide though, and a small hole for a bolt to hold it..
I have found that the signal isn't quite strong enough from some aftermarket tachs, mainly the cheapo ones, but may factory tach works fine with it..
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well gentleman, and lady (if you are reading ;D)
i have a working tach drive system on my diesel..
it idles @ 900
it brings the needle off the 0 peg of the boost gauge @ 1500
it makes full boost a little before 3000..
.060-.070 air gap.. more is better, unless your pickup isnt strong enough to drive the tach.. i have a GOOD autometer tach, so i have no issues.. i really want to see if i can drive a stock VW gasser tach tho..
bracket is made from 1/4" aluminum. its bolted to the block with 2 grade 8.8 bolts. it DOES NOT vibrate.. you can hold the engine at whatever speed you want, and the sensor doesnt even WIGGLE..
this is another one of those builds that makes me want to bang my head on the wall.. ive had all these parts laying around, just not the knowledge to use al of them in a way that works..
anyway, pics to come later.
and NO, there were no issues with triangulation 8)
and people can criticize my build all they want, im not going to change it for anyone.. i will actually welcome criticism, because i am VERY CONFIDENT in my build skills..
i may have not done it the best way possible, big deal.. i made it functional, and transferable to another engine if need be. it IS ADJUSTABLE, and it is very easily removed to gain access to the main drive belt..
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i may have not done it the best way possible, big deal.. i made it functional, and transferable to another engine if need be. it IS ADJUSTABLE, and it is very easily removed to gain access to the main drive belt..
Gee what more can a guy (or gal if your reading this) want? Cost is low, it is out of the way when needed service comes calling, it is above all functional and you can use it other places.
Can't wait for the pictures, I may be following suit here as my ride really could use the tach. I just like em.
Oh I had to come back and thank ya for sperminting for the rest of us. Gasser tachs are a dime a doz but to find a diesel tach and not have the W terminal is like pulling hens teeth.
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i may have not done it the best way possible, big deal.. i made it functional, and transferable to another engine if need be. it IS ADJUSTABLE, and it is very easily removed to gain access to the main drive belt..
Gee what more can a guy (or gal if your reading this) want? Cost is low, it is out of the way when needed service comes calling, it is above all functional and you can use it other places.
Can't wait for the pictures, I may be following suit here as my ride really could use the tach. I just like em.
im with you on this one. a tachometer is my favorite gauge hands down.
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i really want to see if i can drive a stock VW gasser tach tho..
It should.. The only thing I noticed is that the gasser tach seemed slow to respond to RPM increases.. Could have just been my tach too as it did eventually die alltogether...
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thumbs up this is cool, simple and cheap with out having to question accuracy at all. i've done quite a few of the gas tach conversions for myself and other peope, and it works great, how ever i think this method is a bit easier assuming someone has the ability to make a mount for the sensor
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Yes. This is nice I would love to do this, show me pictures so I can copy it. I may have to buy a gauge pod from that guy as I am out of room in my center consol.
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In order for us to really do a good job copying this setup we would like AutoCad drawings please. But a napkin and felt pen will work as well.
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In order for us to really do a good job copying this setup we would like AutoCad drawings please. But a napkin and felt pen will work as well.
if you want auto-cad drawings form me, you may have a better chance of seeing god..
im not gonna completely design this for you guys.. i dont want anyone to COPY my setup. i wanna see who can come up with a better setup in all actuality..
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Also, i didnt use a crank angle sensor in the final build.. i used a cam position sensor off of a different ford engine..
its a more low profile pickup, kinda looks like a wheel speed sensor.
and you dont HAVE TO use the same pickup as me. or even one from a ford. any 2 wire magnetic pickup SHOULD work as long as it can put out a strong enough signal..
if you have a newer GM wheel speed sensor, dont use it, they dont work.. there really small, and fit nicely anywhere, but dont make enough juice to drive a tach..
anyways, pics as promised.
(http://i702.photobucket.com/albums/ww28/Dubsmoke/P1000473.jpg)
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The gautlet has been thrown, better this! OK, let's see how good we can make it. Over the next year or so we should have quite a few folks that can try their hand at this. I for one am putting it on the things to do list. Might end up as a major mod in the future. like the governor mod.
Thanks so much for the work and I know you will be tweaking on this as time goes by. It is just in our nature to do so. That is why we are here in the first place, NO?
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I see red marker...one of my favorite tools since I seemed to always break my crayons :(
I didn't realize that this was all that had to be done. The nuts are just steel and since they are welded off the steel pulley it only reads the nuts? Also, why 2? How does this work electrically speaking as I don't know this end of the spectrum well.
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I see red marker...one of my favorite tools since I seemed to always break my crayons :(
I didn't realize that this was all that had to be done. The nuts are just steel and since they are welded off the steel pulley it only reads the nuts? Also, why 2? How does this work electrically speaking as I don't know this end of the spectrum well.
the nuts simulate the 2 cylinders firing per revolution of the crank. remember, im trying to duplicate a gasser tach signal. and a gasser coil fires twice per revolution of the crank.
the nuts are just a chunk of metal to excite the magnetic coil in the pickup. since its an inductive pickup, it carries its magnets inside it, and requires no external magnets to make a current..
yes, i love sharpies, i have a bucket of them in my shop. most of them being red.. ;D
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Heres one I put on my caddy today, did'nt want to copy yours so heres a little different version.
Sensor is 92 F-250 rear anti-lock. No welder needed for those without one. Works great even with a cheapo tach.
(http://i814.photobucket.com/albums/zz63/dawgsrepo/IMG_0841.jpg)
(http://i814.photobucket.com/albums/zz63/dawgsrepo/IMG_0842.jpg)
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i used my smaller pulley specifically so you guys couldnt copy it to a TEE.. unless you figured out what pulley i was running, and that i had to make a spacer to run it also.. so, it CAN be copied, but you gotta go thru the same hassle i did ;D
if you weld nuts on the outter lip of the pulley like i did, and you are running a stock diesel pulley set, then the nuts will hit the water pump pulley BAD.
most diesels have the bigger pulley setup, i used a small crank pulley with a small water pump pulley.. (underdrive)
i dont know if the pullies on my engine were stock to it (vanagon) or if they were rabbit pullies. i know the crank pulley on there now is off an OLD 1.5D... (like, really old.. the engine i got the small pulley from, originally had manual brakes, just to give you an idea)
i like the setup tho. it takes alot of the guess work out of making the trigger wheel.. only problem i could see, is that the bolts holding the bracket together may vibrate out.. these engines have ONE HELL of a harmonic vibration @ 3k rpms..
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Heres one I put on my caddy today, did'nt want to copy yours so heres a little different version.
Sensor is 92 F-250 rear anti-lock. No welder needed for those without one. Works great even with a cheapo tach.
(http://i814.photobucket.com/albums/zz63/dawgsrepo/IMG_0841.jpg)
(http://i814.photobucket.com/albums/zz63/dawgsrepo/IMG_0842.jpg)
you got a VNT also? or just some other low mounted turbo?
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you got a VNT also? or just some other low mounted turbo?
It's the low mounted GT-15 (prothe's version)
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you got a VNT also? or just some other low mounted turbo?
It's the low mounted GT-15 (prothe's version)
ok, that makes sense.
the GT15, and the VNT15/GT1749 look pretty similar on the cold side..
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Can someone tell me what year of Fords to look on for this crank sensor, and also where abouts on the engine it is located?
I know it's off a 4.0...
And if it's not too much trouble... also what tools are needed to remove it. I don't like lugging a lot of tools around the scrap yard
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The one I did was a rear anti-lock brake sensor from the rear diff housing on a 92 f-250.
You need a 10mm wrench and a pair of wire cutters.
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Kinda like my setup from a few years back ;) ..... see post 29.... http://www.vwdiesel.net/forum/index.php?topic=3741.15 ....I guess you could have come up with it sooner, but it wasn't posted on here.... ;D
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tried this today....gonna keep posted on the workability....basically hooked up an 83 GTI tach to a battery and a ford V8 distributer....no coil no module....just the inductive pickup and trigger wheel....with my 750 rpm drill at full blast the tach registered just under 3K....and was smooth down to almost zero rpm....so I cut six of the trigger "arms" off of the wheel leaving two at 180 apart and buzzed the drill up to full speed...the tacho was smooth reading around 500 rpm....probably could be adjusted out with the pot.....I have already built a bracket to house an inductive speedo pickup from a late model ford tranny....it will be pointing at the four balancer bolts at the front of the crank....two of which will be spaced out so as to trigger the sensor only twice per rev....I'll be working this manana and I'll keep posted (with pics) but looks promising so far :D
OK this works like a charm!!! :D .....for anyone not wanting to solder new caps or resistors on your tach this will work and give an accurate tacho signal with no mods to the tach or calibration of the tach for that matter.....some things I changed from my original idea of pointing the sensor at the pulley bolts was to use two 3/8 nuts welded to the outside of the crank pulley exactly 180 apart and have the sensor pointed at the nut facet with about .020 clearance....the old idea simply had too much bracket hanging over the sprocket add to that thrust clearance variance and it may have thrown off the gap and thus the reading.....good luck!!
(http://i146.photobucket.com/albums/r262/jimbote/tachsender005.jpg)
(http://i146.photobucket.com/albums/r262/jimbote/tachsender002.jpg)
(http://i146.photobucket.com/albums/r262/jimbote/tachsender003.jpg)
(http://i146.photobucket.com/albums/r262/jimbote/tachsender004.jpg)
(http://i146.photobucket.com/albums/r262/jimbote/tachsender006.jpg)
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great addition huh?
what tach you using?
if you have too big of a bracket, you end up with funky harmonics around 3000 revs from the crank..
it makes the bracket just start quivering, then it breaks in the end...
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factory MKI GTI gasser tach, the bracket I built was beefy with no strange harmonics....3/16 thick plate welded together and was still working great when I sold the truck over two years ago :).... Was one of my favorite mods
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factory MKI GTI gasser tach, the bracket I built was beefy with no strange harmonics....3/16 thick plate welded together and was still working great when I sold the truck over two years ago :).... Was one of my favorite mods
well, maybe i just wasnt using a small enough air gap between the sensor, and the pulley..
i was running .060"... it drove my autometer tach just fine.. but not the mk2 gasser stock tach..
maybe i should re-install everything, and try a smaller air gap?
my second iteration of the bracket was 6061-t6 aluminum channel.. the last one was .100 sheet metal, and soft..
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I picked up what I believe to be a speed sensor off a 92ish F250 rear diff. My question is, do I have to weld onto the pulley, or would a pair of earth magnets excite the sensor?
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I picked up what I believe to be a speed sensor off a 92ish F250 rear diff. My question is, do I have to weld onto the pulley, or would a pair of earth magnets excite the sensor?
The sensor is the magnet. You just need to pass two pieces of metal spaced 180 degrees apart by the sensor.
Not sure on the magnet idea, but it would be easy to try with a dvm.
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I'm thinking that a magnet might give a stronger signal, which I need since I need to drive the stock tach (I think anyways)
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You might have to play with the magnets to get them to signal any thing. Don't forget that they have two poles and passing two north or south past each other may not do diddle. The north south combo might get the signal you want.
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factory MKI GTI gasser tach, the bracket I built was beefy with no strange harmonics....3/16 thick plate welded together and was still working great when I sold the truck over two years ago :).... Was one of my favorite mods
well, maybe i just wasnt using a small enough air gap between the sensor, and the pulley..
i was running .060"... it drove my autometer tach just fine.. but not the mk2 gasser stock tach..
maybe i should re-install everything, and try a smaller air gap?
my second iteration of the bracket was 6061-t6 aluminum channel.. the last one was .100 sheet metal, and soft..
I can modify your mk2 gasser stock tach work with your sensor. PM me if interested.
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I have still yet to do this.. Might have to in this upcoming few weeks.
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factory MKI GTI gasser tach, the bracket I built was beefy with no strange harmonics....3/16 thick plate welded together and was still working great when I sold the truck over two years ago :).... Was one of my favorite mods
well, maybe i just wasnt using a small enough air gap between the sensor, and the pulley..
i was running .060"... it drove my autometer tach just fine.. but not the mk2 gasser stock tach..
maybe i should re-install everything, and try a smaller air gap?
my second iteration of the bracket was 6061-t6 aluminum channel.. the last one was .100 sheet metal, and soft..
I can modify your mk2 gasser stock tach work with your sensor. PM me if interested.
no offense, but if i cant do it myself, its not happening..
now, if you feel like telling me how to do it, im down.. but im not gonna pull my car apart, and send you pieces of it.. i just dont feel right letting someone else work on my car..
its like letting someone have sex with your wife.. it just doesnt happen.
im sure you ARE capable of the mods..
i would just rather you share your info with the forum, rather than keep it to yourself and charge for it..
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While it would be nice to share, he is not forced to by-law or anything ;)
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Knowledge is power and with power comes money. Yes, it would be good to share but that kind of kills the spirit of invention, patented parts and competition. All things that made US great. Buy one, take it apart and you will know what he does.
Does Microsoft produce Open Source code? Do other large corporations share their R&D results with Popular Mechanics? Nope! Gotta pay the man, to be on equal footing. Sorry Dude.
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Let's talk about inductive pickups instead...
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I thought I was offering a valuable service. Seems there's lots of idi's out there without a tach and many of those owners would love to have a tach. You do not have to send me the entire cluster, just the tach and the mag pickup. I will mod it and take a video of it working on the bench before sending it back to you.
I do not have any gasser clusters at the moment. If I get more, I will convert them to a diesel cluster with either a W terminal tach or mag pickup tach (pickup included) and offer it it the parts for sale forum
Edit:
For anyone interested in this and do not feel like paying for it, maybe we can work something out in trades for parts?
factory MKI GTI gasser tach, the bracket I built was beefy with no strange harmonics....3/16 thick plate welded together and was still working great when I sold the truck over two years ago :).... Was one of my favorite mods
well, maybe i just wasnt using a small enough air gap between the sensor, and the pulley..
i was running .060"... it drove my autometer tach just fine.. but not the mk2 gasser stock tach..
maybe i should re-install everything, and try a smaller air gap?
my second iteration of the bracket was 6061-t6 aluminum channel.. the last one was .100 sheet metal, and soft..
I can modify your mk2 gasser stock tach work with your sensor. PM me if interested.
no offense, but if i cant do it myself, its not happening..
now, if you feel like telling me how to do it, im down.. but im not gonna pull my car apart, and send you pieces of it.. i just dont feel right letting someone else work on my car..
its like letting someone have sex with your wife.. it just doesnt happen.
im sure you ARE capable of the mods..
i would just rather you share your info with the forum, rather than keep it to yourself and charge for it..
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Haha drill the bell housing and install an mpu like a generator they run off the flywheel teeth. I installed a few before on i drilled bell housings its no biggie.
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Its easier to put in a w lead in an alternator thats a 1.5 hour project for an average. Im sure vdo still makes the diesel tach i got too. Its kinda small 2 inch but the sw i recently dug out is a little bigger
I had it adjusted close at idle but up at 2k it was readin 2200. It still needs further calibration
I've never had any slippage issues or bounce with any w lead powered tach. Well unless your belt is loose but duh tighten your belt then!
(http://i1260.photobucket.com/albums/ii563/hillfolkvwdude/6FA97558-4AA4-4D84-B1E9-A237F4AC9676-315-00000024CFE631A1.mp4)
(http://i1260.photobucket.com/albums/ii563/hillfolkvwdude/0B29B2A3-0A7C-42E9-9990-73B673E1097A-315-00000026025E79A5.jpg)
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This last weekend I worked on installing a tachometer into my '91 ALH Automatic Vanagon. Due to this being an mTDI there is no ECU and so no engine speed signal generated. Some folks use the alt W-signal (unrectified A/C signal) but pulley size differences can cause calibration issues and also mess with the dynamic oil pressure warning system function. To that end I decided to stay with a gasser tach and to generate the necessary 2 pulses per rev to drive it.
Here are the fabbed components I came up with:
(http://i13.photobucket.com/albums/a269/libbybapa/100_2601_zps12d5553f.jpg)
They fasten to the engine like this:
(http://i13.photobucket.com/albums/a269/libbybapa/100_2602_zps8951f324.jpg)
I replaced two of the four crank bolts with studs and coupling nuts and then installed a short bolt into the open end of the coupling nuts in order to read off the flat face of the bolts. The bracket was designed so that I could still access the main crank bolt for rotating the engine by hand:
(http://i13.photobucket.com/albums/a269/libbybapa/100_2604_zpse42cc66e.jpg)
I had a little concern about crank thrust changing the air gap, but it doesn't seem to be an issue. Tach operation is solid. On another install I might be tempted to rotate the sensor so that it is perpendicular to the crank axis and then install two longer bolts into the coupling nuts in order to read off the shanks of the bolts but this works fine for this install. The sensor that I used is part number XR3Z-7H103AB (as provided by Jimbote in the other thread) and retails for approx $25. On my setup, it generates approx 1.9v A/C. I found that it would not drive the stock '91 vanagon gasser tach (arghhh....) but that it works well with an early mk2 gasser tach. I tested the system with a mk1 rabbit tach and it works fine there as well. Oddly enough I have two early mk2 gasser tachs and only one would work with the system. I'm not sure if the one that didn't work was because of a fault with the tach or a difference in design. Although I had to disassemble the instrument cluster to install the mk2 tach, I did not make any changes to the wiring. The probe has two interchangeable connections and one goes to ground and the other goes to the green wire that was previously connected to the WBX ignition coil. I have considered installing magnets instead of the two bolts in order to bump up the signal output in order for it to work with the stock vanagon tach. I'm curious if anyone has any other suggestions.
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No suggestion, but I think what you have done is awesome.
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^^^ Agreed ^^^. I bought that sensor over a year ago and haven't done anything with it, other than look at it.
Any reason you want to make the pick up read off the shank instead of the head?
-Todd
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Any reason you want to make the pick up read off the shank instead of the head?
Radial movement of the crankshaft is less than the thrust motion and so reading perpendicular to the axis will give a more consistent air gap than reading parallel to the axis of the crank. Regardless, the way it is currently set up works fine, so I will not be changing it.