Tach for CUCV

[Keith_J]

I hooked a multimeter up to mine and nothing showed. Not sure if it is not going to show anything or if mine is dead.

I too am interested in working it so I could add a tach for under $50 or use a gas one I have laying around.

It is AC and the tachometer calculates crank speed by the frequency. You have to take into account the pulley (sheave) ratio. Alternators turn 1.5 to 3 times the crank speed. Or more on slower diesels. Usually want to keep the alternator under 10,000 RPM as frequencies above 200 Hz (12,000 RPM on the alternator) make for less efficient generation.

 

[jakwi]

Ok I hooked up an oscilloscope, see picture, to pin D, I also tried F and it looked essentially the same. The picture was taken at, my guess, 1500 rpms.

It is putting out a very dirty and spikey sawtooth wave. the period was approx 300 microseconds which works out to 3.33 khz frequency, It seems to me that I read that the frequency is either 2 or 4 times the RPM, so if that's the case my rpms were either 1666 or 833, 1600 sounds about right.

So I'm going to build this circuit and hook an old 8k sunpro tach that I have up to it and see. The article I read on this circuit implied it might need to be tweaked (for resistor and cap values) to work right. We'll just have to see.

 

[oldmechanic]

found it. this is what I was told to be a optional equipment tach./hr. meter equiped M1028A1 (Sorry for the bad resolution, but this is a a photo of a bad photo) Question? if you use a Humvee tach. drive in place of the vacum pump, then what do you do for a vacum source? I am not familiar with the Humvee set up. Thanks

I have one of these in my spare parts shed if any one is interested let me know & I will dig it out
OM

 

[mtjbrown]

Anyoner on here tried one of these Tiny-Tach: Diesel Tachometers. Just curious if they work well the way they hook up.

 

[AJMBLAZER]

I've actually had those recommended to me over on CK5. Planning on going that route with my two.

 

[jakwi]

Ok I think I found the solution, or at least an easier solution.

I have been modifying my extra alternator to use as a welder since the PO converted my M1009 to 12, so I've been reading alot about the delco alternators. It turns out some of them have an extra pin that is used for a tachometer. (aka W pin) Some of the diesel tach you see for sale actually use this pin. So I got to thinking about it and wondering what sort of output it provides. I grabbed the oscope and took a look. Imagine my surprise when I saw a slightly distorted square wave, which cleanus up into a nice square wave at higher rpms. At idle the Square wave has a period of 3.96 milliseconds which works out to about 252 Hertz. Twice that would be 504, which could be my idle rpm. I don't really know as I don't have a way to verify my rpms! I stumbled accross a program called rpmsound, but I haven't had any luck getting it to work.
RPM from Sound

It's actually designed for propellers, I think, but I was reading about someone who used it to verify their tach on a 6.2 l suburban.

So unfortunately my tach is at home or I'd be trying to hook it up now to see what I get. I'm hoping I can correct the 250 hz to 500 hz or so with the 4 cyl, 6cyl 8cyl switch on the back of the tach. I'll post my progress.

I attached pictures of the square wave, the W pin (connected to the green lead) and the alternator opened up.

 

[jakwi]

Well I hooked up my 8k tach, and it pegged out at 8k imediately with the engine idling. so I switched it to 6 cyl, that brought it down to 7500, and then to 8 cyl which brought it down to 4500. Which seemed promising. so then I reved the engine. I'm guessing I was reving between idle 600 ish to maybe 12 or 1300 rpm, but the needle would go between 4500 and 8k. So I think it is actually indicating 450 rpms to 800 rpms, but really I'm just guessing. It seems like I need a square wave divider maybe divide by 10. The other thing is that I don't know for sure that this tach works properly.

Do you guys have any thoughts?

 

[burbn10]

http://static.summitracing.com/global/images/instructions/atm-2888.pdf

 

[jakwi]

I figured it out. I asked a friend of mine about a divide by 10 circuit, and he suggested that a gas tach already has the circuitry, all I need to do is either adjust it or modify it for my needs.

So I opened up the tach and sure enough there are three pots (aka potentiometers, variable resistors) . One for each position on the tach, 4 cyl, 6 cyl, and 8 cyl) so I recorded the value of the 8cyl pot, 179 ohms I think the other two were progressively lower, so I knew I needed a larger pot.

I went to my local electronics shop and bought a three leg single turn 5 k ohm pot. I bent the center leg over to one end, it doesn't really matter which and soldered them together.

Then I removed the existing 400 ohm pot and replaced it with my 5k pot.

Out to the truck to give it a go. I connected the signal lead of the tach to the W pin on the alternator, and it works like a champ. I adjusted the pot until the tach was idleing at 600 rpm, my guess as to what it is actually doing.

when I rev the engine it reacts as I think it should. I'm going to buy an optical tach so that I can calibrate it precisely.

I also left the glass off as I am going to replace the numbers with 0 to 4000 in 500 increments instead of 0 to 8000 in 1000 increments.

btw removing the glass was tricky, I used very small flat blad screwdrivers to pry off the bezel. It would be very easy to break the bezel.

Although I haven't been in to many tachs I assume that they are all pretty similar, it is really just a matter of measuring the pot for the 8cyl position, and then buying a pot that is ten times the value. Since 5 k pots are much more common than 4 k I just got the 5k. I suppose you could experiment with reisitors until you found the right value, but the pot makes it easy and calibratable. I even drilled a hole inthe housing so that I can calibrate it later with out disassembling it.

Any body with mediocre soldering skils should be alble to pull this off.

Oh and the White pot is the 5 k pot I installed. The metal pots are the original styles

 

[patracy]

I happen to have that very same tach laying around out in the shop, guess I know what I'm going to be doing...

 

[OL AG '89]

This an OLD resurrcted thread, but the first several posts mention a "stock" tach/hourmeter setup on the M1028. I bel;ieve that was for running the PTO. If so, it would make sense that the TM's would cover the how and where for the tach signals. I bought an atoumeter tach that has a strap for the alternator with a magnetic? pickup for the signal. Works great. I haven't verified/calibrated with my STE/ICE but will someday.

 

[jakwi]

I happen to have that very same tach laying around out in the shop, guess I know what I'm going to be doing...

I think it worked really well. I painted over the numbers with flat black, and then went to a hobby store to get white rub on numbers. I relabled it for 4k. After that I reassembled the glass and bezel.

Just a note about calibration. I never did get an optical tach, but the method I used worked pretty well I think.

I used a drive line calculator online to figure out what my RPM's should be at a certain speed. Using a GPS to verify speed, I think I used 60 mph I tweaked the pot in the tach while trying to maintain that speed steady until my tach showed the expected RPMs. It took a few tries, but I think in the end I was within a few rpms of correct.

I'm glad to see someone else is going to give it a try. I think the whole project cost me less than $15.

 

[southdave]

I thought I remembered somewhere that you could replace the vacuum pump with a driver for a tach - maybe off HUMVEE 6.2s. This is a very vague recollection.

Truck

I did that very thing with my 700r4 swap.. there was no need for vac pump with that trans.
There is a tach drive I use the electrical pick option, you can use a mech. tach if you wish like the one in a duce and half

 

[Felix Rufus]

I didn't see any ratio for the tachometer selection. .5 to 1, 1 to one, etc? Anyone know what ratio tach I should purchase.
New here and thrilled to find this resource! I just bought a D30 in excellent condition. Hope to get a picture of her on here soon... Heidi, from Florida (3.

 

[Keith_J]

The alternator tach signal is a roughly sine wave alternating current with frequency between 215 Hz at idle to 1239 Hz at 3600 RPM.

The rotor of the 27 SI alternator has 16 poles, 8 North and 8 South. The crank pulley is 7.75 inches in diameter, the alternator pulley is 3 inches. This makes the alternator turn 2.583 times faster than the crank. 625 RPM is 10.41 revolution per second, with 8 cycles per revolution, that is 215 Hz which can be measured on good digital voltmeters.

 

[Felix Rufus]

The alternator tach signal is a roughly sine wave alternating current with frequency between 215 Hz at idle to 1239 Hz at 3600 RPM.

The rotor of the 27 SI alternator has 16 poles, 8 North and 8 South. The crank pulley is 7.75 inches in diameter, the alternator pulley is 3 inches. This makes the alternator turn 2.583 times faster than the crank. 625 RPM is 10.41 revolution per second, with 8 cycles per revolution, that is 215 Hz which can be measured on good digital voltmeters.

Sweet thx. That's the info I wanted; I'll be hunting a gizmo to get the tach I want to get on the same wavelength as my balancer. I'm far from home, bench racing and you kept me in the game. I'll try to get a clear post on how to set up a non adjustable tach or speedo (to match guages on custom dash, etc,) when I get that done and it's fresh in my head.