flywheel tachometer?

[R.O.R-2.0]

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.

[billybobf]

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

[R.O.R-2.0]

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..

[92EcoDiesel Jetta]

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.

[92EcoDiesel Jetta]

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!

[R.O.R-2.0]

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!

so, i need magnets then..

[rodpaslow]

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. 

[Smokey Eddy]

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)

[RabbitJockey]

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.

[R.O.R-2.0]

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..

[Smokey Eddy]

Thank you kind sir! I'm having a hard time finding neodymium magnets though. I'm gonna try a hobby shop tomorrow.

[8v-of-fury]

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.

[R.O.R-2.0]

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..

[92EcoDiesel Jetta]

http://www.ebay.com/itm/4-Neodymium-Countersunk-Ring-Magnet-1-2-x-1-8-/290610470546?pt=LH_DefaultDomain_0&hash=item43a9bbde92

[Smokey Eddy]

Hard drive magnets are crescent shaped