Tachometer options

[02mx-5]

I want a tach for my doodlebug. The tach will be on either a 5hp flathead or a 6.5 clone. What are my options? I dont have 300 bucks for a tach. I also dont want one that is slow to update the readings. Will a tach for a car work? Like one from autozone. How are the tachs usually hooked up, one wire to the spark plug, a ground, and one to the unit itself? Cant wait to see my options

 

[lemegacool]

the car tachs are to be used with minimum 4 cylinders... other than that the readings would be falsed... there is the "tinytach" but as you said he is slow to update the readings...

yeah tach are hooked to the spark plug and ground...

so basically a digital slow updating rpm/houmeter is probably your only option...

search "rpm hourmeter" on ebay ... should show you some tachs...

 

[Kaptain Krunch]

Or you can buy a cable driven tach and rig that up, most have a 2:1 drive ratio. heres one pretty cheap, prolly wont be the easiest to hook up, but with some ingenuity im sure it would work.

 

[02mx-5]

how does a cable driven tach work? where does the cable get hooked up?

 

[Kaptain Krunch]

thats the rigging part, you would have to hook the cable up to your crankshaft with a 2:1 ratio.

 

[02mx-5]

I mean, how does the cable get hooked to the crank? Wrapped around? I just dont get how the cable can be hooked to a moving part, wouldnt it just get wound up?

 

[Kaptain Krunch]

oh, gotcha, its not that type of cable. I guess you have never seen a speedometer cable. A speedometer cable is basically a long flexible rod that spins inside a housing. heres a picture, the rod normally has square or hex ends that will insert into the speedometer.

 

[EagleTalons]

5" face is a huge gauge!

 

[t0x1k]

I mean, how does the cable get hooked to the crank? Wrapped around? I just dont get how the cable can be hooked to a moving part, wouldnt it just get wound up?

A lot of motorcycles do it this way for both tach and speedometer. I think it's centrifugal force that causes the needle move. Im not sure, i'm talking out my ***.

 

[Kenny_McCormic]

A bicycle speedometer can be used as a 10k rpm tach. http://www.instructables.com/id/Tachometer-made-from-a-bicycle-speedometer-cycloc/

 

[02mx-5]

thanks kenny. I was about to ask if that was possible

 

[BriggsTwins]

Ive been wondering this for sometime now. I was planning on using one for my twin, it will need a filter cap or a small resistor somewhere to help reduce the interference and it might help in controlling a 4cyl tack on 2. still i havent found one for free yet so havent bothered.

 

[02mx-5]

I bought a tach/hourmeter off ebay for like 15 bucks brand new. If its off a little bit in timing thats ok