Tach drive died

[David_Doan]

The mechanical tach drive in my Buggeye died. It had un-screwed itself from the generator, and was just hanging by the cable. I was able to fix it with JB Weld, but it does still bind occasionally, which is why it un-screwed itself.

I want to move to an alternator anyway, so I started looking at tachometer conversions. It looks easy to swap the faces, as some guides suggest. My question is since the old style is 0 to 6000 and the newer ones are 0 to 7000, can the electronic ones be recalibrated?

 

[Sarastro]

The new one won't need to be recalibrated. It will still display the right RPM value; it just has a greater RPM range.

 

[Trevor Jessie]

Steve, he is talking about using the newer guts under the old face... I think.

 

[Billm]

There is a variable capacitor inside the electronic tach that is used for calibration. I usually drill a hole in the case so that I can access it thru the case and then cover the hole with a piece of electrical tape to keep some of the moisture out.
BillM

 

[David_Doan]

The new one won't need to be re-calibrated. It will still display the right RPM value; it just has a greater RPM range.

Steve,

Coincidentally, when I started googling around for info about tachometers, your web site came up. I really like a lot of the stuff you did. I have similar plans for the wiring in my car. In addition to what you did, I want to make an easy disconnect for all the hood (bonnet) wiring so I can pull one plug to remove the hood.

Back to the tach --- Why do you recommend that the “pulse-cleanup” circuit be mounted away from the tach?

Thanks,

David

 

[rkep01]

David - Take a look at this site to see if it might be of some use to you. NFI

 

[David_Doan]

David - Take a look at this site to see if it might be of some use to you. NFI

That looks great, but I'm way to cheap for that.

I had a long layover at the airport today. I found an RVC tach from a late model midget on ebay for about $30.

Hopefully I will be able to transplant the guts into my current mechanical tach that has the same "patina" as my speedo.

I don't think it will be too hard to get the calibration right. I will post my results.

Thanks,

David

 

[Jim_Gruber]

David, I use a 6 Pin trailer Wiring Harness as a quick disconnect with my BE Bonnet on my '68 Sprite. Easy as pie just tie all of the grounds together and you've got enough contact. A Zip tie holds it together. I can remove the bolts on the forward tilt hinge and cut the zip tie, separate the wiring harness and in < 10 minutes using a block and tackle pulley system have the bonnet off of the car by myself.

 

[The_architect]

David, I did exactly what you wish to do. You will have to drill new holes in the face I think, I did. I also followed the MGA Guru's directions for calibrating my tach--ignore the part of this article which shows how to change polarity unless you are going to Electric tach calibration This uses a cheap wall wart as a 60 hz signal source. It worked great. Good luck! Charlie

 

[David_Doan]

David, I use a 6 Pin trailer Wiring Harness as a quick disconnect with my BE Bonnet on my '68 Sprite. Easy as pie just tie all of the grounds together and you've got enough contact. A Zip tie holds it together. I can remove the bolts on the forward tilt hinge and cut the zip tie, separate the wiring harness and in < 10 minutes using a block and tackle pulley system have the bonnet off of the car by myself.

Trailer harness is a great idea.

 

[Sarastro]

Back to the tach --- Why do you recommend that the “pulse-cleanup” circuit be mounted away from the tach?

It's not critical, but if you mount it near the tach, you have to run the wire from the points side of the coil to wherever it is, and that wire carries a couple hundred volts. It's a lot safer, in my opinion, to run the triggering wire to the tach (a few volts) and keep the cleanup circuit near the coil. It also won't kill the ignition if it shorts to ground at some point.

That said, in my Porsche, the "hot" lead runs from the engine, in the rear, to the tach, in the front. So, it's not unprecedented.

Sorry I misunderstood the question. You can recalibrate, but I suspect it will require changing parts. If you understand the electronics, it's easy, but if not, it might be a lot harder.

 

[David_Doan]

It's not critical, but if you mount it near the tach, you have to run the wire from the points side of the coil to wherever it is, and that wire carries a couple hundred volts. It's a lot safer, in my opinion, to run the triggering wire to the tach (a few volts) and keep the cleanup circuit near the coil. It also won't kill the ignition if it shorts to ground at some point.

That said, in my Porsche, the "hot" lead runs from the engine, in the rear, to the tach, in the front. So, it's not unprecedented.

Sorry I misunderstood the question. You can recalibrate, but I suspect it will require changing parts. If you understand the electronics, it's easy, but if not, it might be a lot harder.

Thanks, I'm comfortable with electronics. If I can't get the factory electronics to do what I need, I'll do something similar to what you wrote about in March 2009. Great writeup btw.