Tacho testing without a running engine. (That's a tachometer, not the spicy thing from Mexico)

With 100hz supplied from an old battery boiler, we begin in earnest, if you're elsewhere you could have 120hz to play with. At 50 hz AC mains frequency, with full wave rectification you end up with 100hz. So that's 6000 per minute. Now the more pedantic of you will point out that it ain't exactly 50hz, the frequency varies throughout the day. That said due to parallax error, the pointer isn't always where it appears either. So in short, if you need a better reference source, buy one.
100hz x 60 sec = 6000 lumps of electric every minute.
If we need 2 lumps for every turn of the crank on a 4 stroke, 4 cylinder, that's 3000 rpm with conventional single spark technology. If you're running coil packs, get a responsible adult to work out the maths for you, same with a V6, I can't be arsed to do the maths.
This should work on most tachometers, mine has inputs for contact breakers, sink and source ECU signals and AC from the W terminal of an alternator. A bit of common sense should tell you what to use. The instructions are always handy and will aid you build a rest rig. For example, if it were meant for the W terminal of an alternator, pick off an AC from the secondary of the transformer. If you don't know what I just said, don't go messing with it. Adjust the maths if you're on 60hz.
The scope was just to show the ripple for those who haven't seen it before, you don't need it. Just a battery, a battery charger and the tacho are all you need.
Obviously if you end up blowing the smoke seals, killing your first born or get confused beyond the point of no return, it's not my fault.

[@Good-Enuff-Garage]

came here for the subtle humor, left with tach testing know how! well played mate, well played

[@v8trauma]

No problem, thanx for the comment.

[@carlosmaldonado8600]

Very practical!!!! Thanks

[@v8trauma]

Carlos Maldonado no worries. Just remember, this is for a 50Hz mains supply. 60Hz will give you 3600 rpm on a 4cyl 4 stoke. It's easy enough to work out what to expect from your supply. The more cylinders you have, the lower the reading will be. It's not a calibration, but more of a functionality check. Works with speedometers too, but that's a video for another day.

[@user-nsixfour]

Hey i saw you have a gas drill on one of your other youtube comments is it for sale or do you have any other gas tools you are interested in selling?

[@v8trauma]

It has sentimental value, so no, but thanx for the offer.

[@silentwarrior79]

Lol

[@John98512]

You like to hear yourself talk

[@v8trauma]

You like to be a keyboard warrior.

[@John98512]

@@v8trauma not really.

[@v8trauma]

@@John98512 no, really.

[@John98512]

@v8trauma you can take it as you wish. An improvement would have been to get to the point without being cute.

[@v8trauma]

​@@John98512 finally some constructive criticism from you. I'm sorry the free content and education I provided didn't meet your rigid standards. I made one about pizza you'll absolutely love th-cam.com/video/1DMNEcXgCso/w-d-xo.html
I will try better next time, I may even give you a shout-out, though please don't take this the wrong way, I did feel flattered that you said I was cute, but I don't think you're my type. Let's keep this on a purely platonic basis. So going forward, if I make the free content as and when I like and within youtube rules, you can keep carping from the sidelines. After all, the algorithm sees any interaction as a good thing and anthing you have to say really helps me out.