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Engine Specific Info and Questions => IDI Engine => Topic started by: Smokey Eddy on April 28, 2012, 12:25:07 pm
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I have a sensor that will spit out a signal when a magnet passes by it.
If I inset a strong rare earth metal magnet into the flywheel, could I read rpm through the peep hole on the transmission?
I would be feeding this output signal to a tach I bought years ago that just looks for a signal on a wire. Its a Sunpro tach.
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I don't see why it wouldn't work, but are you sure the tach needs to see only one voltage spike for it's signal? Not saying it won't work, but most tachs take a signal off a distributor, and they're timed for a specific cylinder number. It might work if you put 4 magnets in the flywheel to replicate a 4 cylinder engine then it might work. The other thing is making sure the sensor is a certain distance from the flywheel, but you probably already know that. Are you sure the sensor will have a sufficient output to trigger the tach?
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No, I have no idea. I also have no idea how I could test anything without a frequency generator and scope. If I recall I remembber there being a switch on the back of the tach to specify the number of cylinders. 3 more sensors would be pricey. It might be easier to make a multiplier.
I forgot the fact that the tach is looking for a signal from a distributor. Flip.
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A 4-cyl sees two pulses per crank rotation. Two magnets would be easier than two sensors.
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Deeerrrrrrr of course. I'm not thinking clearly today.
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You're in Canada, wouldn't it be easier to to find a factory VW diesel tach to run off the alt W terminal?
If you want to run off a magnet(s) on the flywheel, here are some tips from actual experience:
In my EcoDiesel, I have been running a gasser VW CE2 tach with 2 magnets on the harmonic balancer for a few years now. It works great as long as the magnets stay put. One of them keeps flying off and the tach would read 1/2 actual rpm until I glue another magnet back on. If you put magnets on the flywheel, the centripetal force is much greater than on the harmonic balancer so you would need to secure the magnet(s) much better for it to stay put. I'd suggest tapping the flywheel and use a machine screw instead of glue. Before you do all that work, I'd strongly suggest testing in with a disc with magnets on a drill to make sure the tach works first.
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Re: point #1, they go for around $100 if you can find one.
Re: point #2, very sound advice. I did try this tach set up with the pulley from the crank shaft but i also had a hard time keeping the magnets in place. What kind of glue do you use? I tried to make a tapered hole and press the magnets in which lasted for a few days of driving but the magnet dissapeared before i finished the mount for the sensor. The pulley is alluminum however which after being replaced with a neodymium magnet i would imagine the balance would be off. Not enough to really matter though i don't think... (thoughts on that?). I think i'll change my timing belt and water pump gasket soon (when it really heats up) and at the same time i'll drill 3 more holes for magnets and give it a go. since the pulley is aluminum i think i'll peen the alluminum over the magnets a bit to help keep them in place. Maybe some JB weld in there for glue would help also. Suppose I'll have to rough up the magnet too so it has something to grab onto.
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I vote for using a tap and bolting them on, with a small screw.
Using a tap to make a threaded hole is easy once you get the hang of it and you don't have to buy a whole tap set if you don't want to, just the size you want and something to turn it.
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loosing them off crank.. glad they not in your timmingbelt...
on flywheel... i see hole in tranny case... not lots of room for it to fling off..
i think alt fan best.. heat up red hot.. dimple for mag spot.. let it cool.. press magnet in..
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Re: point #1, they go for around $100 if you can find one.
Re: point #2, very sound advice. I did try this tach set up with the pulley from the crank shaft but i also had a hard time keeping the magnets in place. What kind of glue do you use? I tried to make a tapered hole and press the magnets in which lasted for a few days of driving but the magnet dissapeared before i finished the mount for the sensor. The pulley is alluminum however which after being replaced with a neodymium magnet i would imagine the balance would be off. Not enough to really matter though i don't think... (thoughts on that?). I think i'll change my timing belt and water pump gasket soon (when it really heats up) and at the same time i'll drill 3 more holes for magnets and give it a go. since the pulley is aluminum i think i'll peen the alluminum over the magnets a bit to help keep them in place. Maybe some JB weld in there for glue would help also. Suppose I'll have to rough up the magnet too so it has something to grab onto.
If I were you, I'd spend the $100 and buy a W terminal tach. ;)
I used crazy glue and epoxy. Strangely, only one of them keeps flying off (the same one) so it must be bad surface prep. My harmonic balancer pulley is steel (magnet sticks to it). You sure yours is aluminum? I don't think there is enough meat to tap the pulley for a screw, it would go through and hit the belt. Not sure if you can tap the flywheel either. Wouldn't it hit the starter motor gear?
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I'm sure there is plenty of meat on it. The belt only goes around the edge. Do the magnets really have to be on the edge? As long as you get 2 passes/revolution and the sensor is mounted above the surface, wouldn't it work? With long enough magnets or a bracket it would still reach the edge. I would worry more about it not being balanced.
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They don't have to be on the edge. My magnets are on the edge of the pulley (actually sticks out beyond the edge about 1/8"), which makes making and mounting the bracket for the pickup and changing the pwr steering belt much less complicated .
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loosing them off crank.. glad they not in your timmingbelt...
on flywheel... i see hole in tranny case... not lots of room for it to fling off..
i think alt fan best.. heat up red hot.. dimple for mag spot.. let it cool.. press magnet in..
My magnets are on the harmonic balancer, not crank, so no fear of magnet jamming the timing belt.
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http://www.vwdiesel.net/forum/index.php?topic=30442.0 (http://www.vwdiesel.net/forum/index.php?topic=30442.0)
hope some of that helps.. because it worked for me.
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Kind of off topic but I've been wanting to use a reflective surface,.. like the laser tachs use.
Completely different sensor,.. but no magnets to fly off.
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loosing them off crank.. glad they not in your timmingbelt...
on flywheel... i see hole in tranny case... not lots of room for it to fling off..
i think alt fan best.. heat up red hot.. dimple for mag spot.. let it cool.. press magnet in..
My magnets are on the harmonic balancer, not crank, so no fear of magnet jamming the timing belt.
my magnets are IN THE SENSOR.
there are nuts welded to the outter rim of my pulley, they arent going to ever fly off either.
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Ok, so I know that on most of those flywheels there is a little tang that sticks out a little, I also know that you can get a magnet switch. what if a magnetized switch could pick up that tang, or an optical sensor would work.
Ok, I wonder myself, if the w terminal is working accurately and then you put HIGH draw on the alt, would the friction make the alt inaccurate?
what about the fact that one pulley might wear to a different size at a different speed?
Also, could a wider belt or a tighter belt tension mess with the accuracy of the w terminal tach?
WHILE TYPING... last post was made
so his sensor would work with the flywheel tang but would only be ONE on the flywheel tang
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you guys are at the wrong end of the engine, i would not even try and get a reading off the flywheel. you start adding weight to the outter edge of it, and things become unbalanced real quick..
you add a couple small nuts to the outter edge of a 4.5" pulley, and its not going to need to be super duper accurate balanced..
im not saying my method of driving the tach is the BEST, but it is EASY, VERY CHEAP, and done with normal tools and parts, nothing special..
my setup uses a VERY EASY TO OBTAIN cam position sensor from a SOHC 4.0L ford V6.. it works great, but its not strong enough to drive a stock gasser CE2 tach..
idk, you guys can mess around with optical sensors all you want, but its not necessary i dont think.
again, i wouldnt ADD ANYTHING to the flywheel, unless you have it balanced after you do..
a couple grams added to the edge of the pulley (spaced 180* apart, to counter balance each other) isnt gonna do squat, its not gonna cause any bad harmonics to crack your crank, or anything fun like that..
a couple grams added to the outside edge of a 15" flywheel, and only using one magnet, or sensing device..
and yes, the alternator W signal is very prone to discrepancies.. if your belt gets wet, and slips, the tach doesnt read. if your pulleys wear to different dimensions over time, its not accurate, as your belt wears, it changes the accuracy. as you load/overload the alternator, the accuracy changes.
in my opinion, the W signal is basically useless if you want a REAL number for your RPMs.. it just gives you a GENERAL IDEA of how many RPMs you MIGHT be turning. could be more, could be less..
and i KNOW FOR A FACT, that my tachometer setup that i built, was 100% accurate.. tested its accuracy against scirocco.org/gears, with a GPS, and it was dead on accurate..
im not trying to push my way of driving the tach, but its easy to do, and it works with any after market tach..
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Whatever you use for a mag pickup, triggers (nut, magnet), and tach, test it on the bench first to make sure it works before you install it on your car. A cheap easy way to test is to mount the nuts or magets on a washing machine motor (usually 3600 rpm @ 60 hz) and see if the tach reads 3600 rpm.
With my VW gasser CE2 tach and the mag pickup I am using (from a Mercedes), I had to use magnets. A nut did not provide high enough output from the mag pickup nor did Alnico magnets, I had to use Neodynium magnets for it to work. Even then, I had to modify the gasser tach circuitry to make it more sensitive. It was a lot of work but I wanted a tach in my CE2 cluster, not a standalone tach mounted elsewhere. If I was able to find a VW diesel W terminal CE2 tach, I would have gone that route.
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One of the magnets fell off again a few days ago for the 3rd or 4th time in 3 or so years. Instead of gluing it back on with crazy glue and epoxy, I am trying crazy glue and RTV silicone. RTV is much more pliable than epoxy and I hope will work better. Only time will tell.
Here's a video of my gasser tach, cruising in 5th @ 45 mph doing about 2200 rpm. It's nice having a tach in the cluster where you can see it easily.
CLICK TO PLAY!
(http://i1183.photobucket.com/albums/x480/Ecodiesel92/th_VID_20120430_102719.jpg) (http://s1183.photobucket.com/albums/x480/Ecodiesel92/?action=view¤t=VID_20120430_102719.mp4)
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One of the magnets fell off again a few days ago for the 3rd or 4th time in 3 or so years. Instead of gluing it back on with crazy glue and epoxy, I am trying crazy glue and RTV silicone. RTV is much more pliable than epoxy and I hope will work better. Only time will tell.
Here's a video of my gasser tach, cruising in 5th @ 45 mph doing about 2200 rpm. It's nice having a tach in the cluster where you can see it easily.
CLICK TO PLAY!
(http://i1183.photobucket.com/albums/x480/Ecodiesel92/th_VID_20120430_102719.jpg) (http://s1183.photobucket.com/albums/x480/Ecodiesel92/?action=view¤t=VID_20120430_102719.mp4)
so, i need magnets then..
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If you're willing to spend a $100, I saw earlier in the post, dakota digital will adjust the w signal from the alternator to run your gasser tach. I though about fiddling around with magnets or using the teeth on the flywheel, a lot of that ends up being problematic as this post shows.
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Kevin it was made clear on the first page that magnets or using the W off the alternator was the best option.
For $100 you may as well just buy a ce2 cluster with a tach from someone.
I'm going to put 4 magnets in the pulley on the end of the crank and go that route. I already have the sensor and the tach is already pressed flush into my dash... (regrets regrets)
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you guys are at the wrong end of the engine, i would not even try and get a reading off the flywheel. you start adding weight to the outter edge of it, and things become unbalanced real quick..
you add a couple small nuts to the outter edge of a 4.5" pulley, and its not going to need to be super duper accurate balanced..
im not saying my method of driving the tach is the BEST, but it is EASY, VERY CHEAP, and done with normal tools and parts, nothing special..
my setup uses a VERY EASY TO OBTAIN cam position sensor from a SOHC 4.0L ford V6.. it works great, but its not strong enough to drive a stock gasser CE2 tach..
idk, you guys can mess around with optical sensors all you want, but its not necessary i dont think.
again, i wouldnt ADD ANYTHING to the flywheel, unless you have it balanced after you do..
a couple grams added to the edge of the pulley (spaced 180* apart, to counter balance each other) isnt gonna do squat, its not gonna cause any bad harmonics to crack your crank, or anything fun like that..
a couple grams added to the outside edge of a 15" flywheel, and only using one magnet, or sensing device..
and yes, the alternator W signal is very prone to discrepancies.. if your belt gets wet, and slips, the tach doesnt read. if your pulleys wear to different dimensions over time, its not accurate, as your belt wears, it changes the accuracy. as you load/overload the alternator, the accuracy changes.
in my opinion, the W signal is basically useless if you want a REAL number for your RPMs.. it just gives you a GENERAL IDEA of how many RPMs you MIGHT be turning. could be more, could be less..
and i KNOW FOR A FACT, that my tachometer setup that i built, was 100% accurate.. tested its accuracy against scirocco.org/gears, with a GPS, and it was dead on accurate..
im not trying to push my way of driving the tach, but its easy to do, and it works with any after market tach..
i would just like to defend the w terminal here a bit, belt wear won't change the reading, only slippage or a worn pulley will do this. Load on the alternator will not effect the tach reading either it works by detecting each time one of the 3 coils in the alternator puts out a voltage, the loading won't effect how often that happens. your method for getting a working tach is the best imo, i've converted tons of gas tachs to work on the w terminal and they work great undoubtedly, but the sensor is probably easier, all you gotta do is add the magnets and the sensor, run one wire, and add the glow plug light to a gas cluster.
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Kevin it was made clear on the first page that magnets or using the W off the alternator was the best option.
For $100 you may as well just buy a ce2 cluster with a tach from someone.
I'm going to put 4 magnets in the pulley on the end of the crank and go that route. I already have the sensor and the tach is already pressed flush into my dash... (regrets regrets)
4 cylinder only fires 2 times per revolution, not 4 times.. so only 2 magnets will be needed..
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Thank you kind sir! I'm having a hard time finding neodymium magnets though. I'm gonna try a hobby shop tomorrow.
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Thank you kind sir! I'm having a hard time finding neodymium magnets though. I'm gonna try a hobby shop tomorrow.
Old hard drives.
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Thank you kind sir! I'm having a hard time finding neodymium magnets though. I'm gonna try a hobby shop tomorrow.
Old hard drives.
those usually arent of useable shapes tho..
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http://www.ebay.com/itm/4-Neodymium-Countersunk-Ring-Magnet-1-2-x-1-8-/290610470546?pt=LH_DefaultDomain_0&hash=item43a9bbde92
(http://i.ebayimg.com/t/4-Neodymium-Countersunk-Ring-Magnet-1-2-x-1-8-/01/!BwTlK5gEGk~$(KGrHqEOKnQEvyFr)DIMBMIU!!4f7w~~_3.JPG)
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Hard drive magnets are crescent shaped
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If you're willing to spend a $100, I saw earlier in the post, dakota digital will adjust the w signal from the alternator to run your gasser tach. I though about fiddling around with magnets or using the teeth on the flywheel, a lot of that ends up being problematic as this post shows.
It really isn't that bad. It takes me 2 minutes to glue a magnet back on. Once I figure out the best glues to use, there won't be any more issues
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so, i need magnets then..
I thought your tach is working already??? Why do you need magnets?
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so, i need magnets then..
I thought your tach is working already??? Why do you need magnets?
my AUTOMETER tach works with a simple magnetic pickup.. my VW CE2 does NOT however.. it will be needing magnets..
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my AUTOMETER tach works with a simple magnetic pickup.. my VW CE2 does NOT however.. it will be needing magnets..
Have you thought about doing things to up the output of your magnetic sensor? The first that comes to mind is try a new sensor. Low output is a typical failure mode. The next thing that comes to mind is to decrease the gap between the sensor and your "reluctor". Magnetic ignition pick ups usually are gapped at .010-.015". Making the edges of your reluctor sharp will also increase the output, as well as making the valleys lower between the "points". Perhaps making the nuts taller so that they stick out father from the pulley would help. I understand that you have some space constraints. I am planning to use a similar set up on my LBGTD. (As opposed to LGBT)
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my AUTOMETER tach works with a simple magnetic pickup.. my VW CE2 does NOT however.. it will be needing magnets..
If after changing to magnets, and you have adjusted the gap to be the smallest possible, and your CE2 cluster still does not work, PM me and I will tell you what mod you have to do to your cluster to make it work.
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How about just posting the mod since I will be dropping an AAZ into an '86 GTI sometine in the next week or so and a functional tach is at the top of my list.
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How about just posting the mod since I will be dropping an AAZ into an '86 GTI sometine in the next week or so and a functional tach is at the top of my list.
cause your 86 doesnt run CE2 wiring, DUH...
the 86 uses a CE1 cluster, witch gets its signal right from the coil..
the CE2 cluster gets its signal from the digifant ECU..
CE1 and CE2 clusters are TOTALLY DIFFERENT dude..