The Stovebolt Site Forums The Parking Lot Big Bolts Tachometer distributor drive.

Need help from the big boys. More familiar to the engine driveline forum but I am facing a deadend.

I want to install a mechanical tachometer on a 261 to make sure I see what revs I am pulling. Most electronic tachs have a scale of 7 or 8000rpm........ 4000 rpm mechanical tachometer are readily available on EPay.... but no drives are ever available.

So my question is how did GM set up the old fashion mechanical tach drives??? the ones I have seen on 361 Chrysler were gear driven from the dizzy. What should or where should I be looking..??

Or..... does anyone know of a low rpm tach that is electricaly driven.

Engine is in a 1940 Chev Canadian Military Pattern 4x4 right hand drive 15 cwt (3/4 ton) truck..... top speed 45 mph with a 216... hoping to top 50 mph with a 261..... but really need to see what is happening under the hood at different speeds. Axles are 6.39 on 16 inch rims. I have used the tire diameter formula to estimate road/engine speed but want to monitor while driving.

Thanks for your help.

Bob Carriere
Ottawa, Ontario

Perhaps the early corvettes used a distributor tach drive with the 6 cylinder?

If you just want a tach and don't have to have a mechanical one try http://www.tinytach.com/tinytach/index.php I had one in my truck for a while, very easy to install and mount, small too. Worked great for my needs.

If you want a nice electric pickup tach with about 3,500 max try Stewart warner, I will be buying one from them for my diesel truck.

Grigg

Rac1812.. check with Virginafiretruck on the 4K tach he has on his pumper panel. I asked him about it and he gave me a name but I've lost it. You might do a search on it as it was posted here.

I think the early 6 cylinder Corvettes used a generator drive tach. The distributor drive came along with the 56' model V8 cars. I've only been getting a little into Corvettes for the last couple of years so I may be wrong but I do know that FI vettes', beginning in 57' also used the generator because the Rochester fuel pump ran off the distributor. Not exactly Stovebolt material is it?...but what the heck.

Thanks for the leads... will follow up and get back here.... I think the fire truck has a commercial application most likely to fit my need with existing 4K rpm.

Dave I beleive the deisel 3500 is fired from the alternator... which I can't undertand.

At 50mph flat out the engine should run at just under 3K... probably higher in lower gear.... so I think 4k is more appropriate... friend has downloaded S-W catalogue so I cna check it out.

Thanks for your help.

Bob C

I got your message. Here is the rebuilt Tach:

http://rides.webshots.com/photo/2896660240080243953BkudSM

Here is the wiring diagram:
http://rides.webshots.com/photo/2753742480080243953xyrPLo

I had it rebuilt here: http://www.bobsspeedometer.com/bobs/

It was added by the firetruck builder(Oren) in 1952. When I went to rebuild it, I discovered they no longer make the battery that went into the firewall mounted part. I had to have the guts removed and electronic modual installed. From the outside view, you'll never know the difference.

The diesel tachometers that get a signal from the alternator are normal. The alternator has an extra terminal for a wire to go to the tach. Not all alternators will work, but if you go to a good starter generator and alternator repair shop they will understand completely and should set you up.
The other option is a tach that uses a sensor like an electronic speedometer. The sensor is most often mounted in the flywheel housing and reads from the ring gear. This is the version I will use on my truck, my flywheel housing has a boss ready to be drilled and tapped for the purpose.

Grigg