Tachometer rebuild Options

[mepstein]

These just showed up today. I always wanted a set of green gauges and these are from a 66-912. 1/3 the price of green 911 gauges.

I assume you are putting them in a 914-4? What is involved? Thanks

I think they should just switch over. Everything looks pretty similar to the stock gauges and they are from a four cylinder car so the tach is the same.

[Larmo63]

I don't get the 'need' for a 10,000 RPM tach. The car won't spin that high, hell, it won't even spin 7,000 RPM for that matter.

My tach is a 914-6 sourced unit, and I use the Tach-Adapt from Bob Ashlock. He tested my tach on his bench to show me
empirically how un-accurate these VDO units actually are.

Bob is a great guy, and VERY brainy. He has a bitchin 912 too.

[totle]

Great looking cars Lawrence :-)

10k is not needed, but correct if you are building a 914-6 GT replica.

I will build a engine for 8k rpm, to have in my GT replica.
That is why I also would like to have the GT periodic correct Tach :-)

[Spoke]

Tach bounce. Now there is something that I would like a DIY solution for. I like the tach scale I have, the tach matches the # cylinders in the engine, but the lazy tach needle and bounce can't keep up with the changes in engine speed.

I would like to know how to fix the bounce too

Here's a simple way to dampen later (73+) tachs by adding a single capacitor of value 1800-2200uF across the windings of the needle. I've done this on a couple of tachs. Works well and simple to install. Maybe not the best or elegant solution but works well as the clips below show the difference between original and dampened operation.

The early tachs internally are different and I didn't spend much time trying to figure a simple way to dampen it.



BEFORE:

https://www.youtube.com/watch?v=VCgLzBJxoEM


AFTER:

https://www.youtube.com/watch?v=VFTXRVlUuyg

[914forme]

You all make me (IMG:style_emoticons/default/av-943.gif) I tried to stay out of this topic I got hooked. (IMG:style_emoticons/default/headbang.gif)

Tim's solution works great. Would love to change all internals to modern servos. I mean all of them.

This allows for all the odd modifications people like to do to these cars.

10K Tach is worthless if the engine can not spin above 8 K. Just place your red line at 8K, I could sell you a face for less than the $100 price mark and it would work. I get doing a 10K tach for a GT car, but still, it is an 8K tach, use the stock tach and modify the face, and internals done.

As Larmo and Bob have stated the VDO tach really is a placebo it can be way off from the factory. Spokes simple solution works to solve the tach bounce.

One issue with Tim's method is the tach can go a full 360 degrees not bad if you have a stock tach in place. Bad if your using a 930 Tach or adding a gauge in the bottom of the tack for fuel, voltage, Amperage, etc.....

So you want to make a 10K Tach that is built from less than $100 - here is your answer.

Layout the new gauge face onto the stock tach, I would suggest using software for this that allows to layout a face based off degree.

Figure out how you want to do the face.

I have messed with all the following
Silkscreening - original method, and time consuming, but can be made to look correct or look like a (IMG:style_emoticons/default/barf.gif)

Transfer method - great for making one off stuff, very time consuming and can be extremely frustrating

vinyl masking - like silk screen - looks great, I can tell you removing every mark and letter can take for ever, then you airbrush the face, and peel off the mask, (IMG:style_emoticons/default/wacko.gif)

Laser etching, if you want aluminum letters or use a different plastic face, fast, efficient, you really can not paint two layers and get this to work right. You would think this is the cat meow, but in the end I killed this cat.

Right now I am messing with printer technologies using multiple substrates and printers. Still trying to find the right mixture and combination. I have two promising methods with this system. One from Bob on here has been extremely helpful with his method.

Sunpro Tach movement or stock. Figure out the proper resistor or add a variable resistor to find the magic resistor to get your full sweep. Get a low frequency pulse generator to make sure your Tach matches with your calculated degrees and the RPM you envisioned. Adjust until you get it right. Due to age the stock tach might not be accurate through the entire sweep. If it was me I would make damn sure the Red line reads accurate or even above / below the red line. Example your read line is 8K I would want it to be really 7800 RPM not the real 8000 RPM. So the real number is above the actual value. Or the Actual value is below the printed number. All perspective B.S. Way safer than blowing up an engine. I also install rev limiters in my cars
But I will say once all that is done as a DIY you could pull this off for less than $99, if you do not count your time.

Enjoy . (IMG:style_emoticons/default/screwy.gif)

I do know what I would charge to produce one, and well it ain't cheap, and I am only doing the ones I have in queue right now. I am back logged like crazy (IMG:style_emoticons/default/wacko.gif)

[timothy_nd28]

Sounds like Stephen is all in with this project, we should expect some custom face dials from him within the week! (IMG:style_emoticons/default/biggrin.gif) That masking method sounds absolutely insane, I wouldn't have the patience for something like that. The laser etching sounds promising, could this be done on some plastic poly, so that the tic marks and lettering could be illuminated from the backlight? Could that also be done so the gauge still looks stock during the day?

The capacitor across the motor windings is very interesting. Our tachometer has been mapped out on the TINA circuit simulator, when I get a free minute, I'll plug in the capacitor with the values you spec'd out to see how it performs.

The stock tachometer does have limitations with folks doing different engine combinations. My tach hack solution was developed to kill many birds with one stone. Updating to a servo style motor is huge, no tach bounce, dual input voltage circuitry to allow for low 5 volt inputs and also high voltage from ignition points, configurable of number of cylinders, and most importantly being cheap, 30 dollars! I made this hack public to the forum to help fellow teeners with their project.

The 10k tachometer is silly for a stock 4 engine. Over that past 3-4 years, I've only been asked a few times about recreating one. However, I do like helping people out and sounds like a fun project.

[914forme]

Yes you use an opaque poly sheet with a matte black upper finish. Then it is just getting the proper laser feed rate to to make the black go away, and then you can back light at night and have the front look almost stock during the day.

The issue I have with the design is the plastic sheet needs to be thicker than the metal it is replacing so you start to have the needles closer to the face. And if doing a 904 3 port gauge or even a quad gauge you can not do a recessed window with out the opaque section showing up. It is as easy as a CNC router to up the radius on the edge. I guess you could paint it.

Maybe I should try it again, fire up the laser cutter and see what we get. Would be a fun little project.

(IMG:style_emoticons/default/headbang.gif) Why the hell do I like doing this (IMG:style_emoticons/default/stromberg.gif) It keeps me from getting other stuff done (IMG:style_emoticons/default/headbang.gif)

I need to buy a few more of the sunpro tachs I have an (IMG:style_emoticons/default/idea.gif)

[timothy_nd28]

I was totally kidding, this project is cool but no where as cool as your triple gauge kits. Trond from Norway just sent me a vector image of the 10k tach face. I'll PM you this image. I think we will try the route of printing off a vinyl decal and just see how it goes.

Also, the sun pro tachs are not being sold anymore, however, I hear the Bosh FST 7904 tach is its equivalent.

[914forme]

I just picked up a bunch of various tacos to give a try.

Yeah send me the vector image I'll load it up and see what it looks like, and get a set printed up. I'll post a pick, and then people can let me know how many they want.

[stownsen914]

I didn't read through the whole thread, but in case it's not mentioned here, there have been some other threads on dash refacing. User omtimusglen has an SVG file that I believe he has offered to share, and that I suppose could be updated to 10K RPM. I'm hoping to do that using guts from a cheap 10K tach for a vintage racer build. I can't fathom dropping $600+ on a gauge rebuild/upgrade.

Any chance of sharing the 10K RPM image?

Scott

[914forme]

Maybe it is not hard to draw up with a vector software or a CAD program. The files I got did not have a red line, so that would need to be added.

[914forme]

It is also not clocked, which I prefer to do on a race car, I know most people just turn the gauge, but if your doing it, clocking the face makes sense. (IMG:style_emoticons/default/confused24.gif)

[mepstein]

I didn't read through the whole thread, but in case it's not mentioned here, there have been some other threads on dash refacing. User omtimusglen has an SVG file that I believe he has offered to share, and that I suppose could be updated to 10K RPM. I'm hoping to do that using guts from a cheap 10K tach for a vintage racer build. I can't fathom dropping $600+ on a gauge rebuild/upgrade.

Any chance of sharing the 10K RPM image?

Scott

He did share it. You just have to email him. I played with it a bit and got pretty close to what I wanted but not perfect. But I was just playing around, didn't read the instructions and I'm not a computer guy.

Even though the 10K dial isn't cheap at around $100+, it can take a huge amount of time to diy and all the materials add up. Stephen and Timmothy have put many hours and dollars into their products.

[mepstein]

Maybe it is not hard to draw up with a vector software or a CAD program. The files I got did not have a red line, so that would need to be added.

the 10K tach on the 911 RSR had a redline. The one on the 914-6 GT did not.

[914forme]

Never knew that, thanks Mark

[914forme]

Duplicate Post

[mepstein]

Never knew that, thanks Mark

Now the tach on the 2 factory 914-8’s has a redline but with a 908 engine, it actually spins close to that number. - coolest 914’s ever built!

[mepstein]

10k tach for sale on the bird.

http://forums.pelicanparts.com/porsche-911...ometer-f-s.html