Ins and outs of Mechanical tach installation

[Original Poster]

Original post....

[mike curnow]

Raj
The 73 RSR parts book shows an optional mechinical tack for that car and the 74-75 RSR. I have one for my car. Its the same size as the 911 speedo. The factory also made a spacer ring to mount the tack in the dash. I'am told the factory did not trust the electric tacks in the factory cars since sometimes when they go bad they create missing in the engine, I have had this happen to me over the years. The tack is black face, white numbers by VDO, but with a Smiths chronometric drive inside. This causes the needle to move in a non lineair fashion. Pretty cool.
The tack is driven from a right angle drive off the passenger cam. I guess if you run a engine oil cooler it might be in the way of hooking up the drive? However if the drivers cam turns in the same direction as the pass cam then you could put the drive on the driver side? However you could not run MFI. I have never seen an aftermarket set up. I do however have a Jones chrono setup that works just like the factory set up, its black an white and the size of the 911 electric tack. The VDO tack has a tel tail and reset button, I believe the Jones does also, I haven't looked at it for a while. I can send a picture in a week or so, have a foot problem and cannot get around at the moment

Mike

[mike curnow]

I can take pictures in a few days.

mike

[mike curnow]

Thanks Raj
In one of the pictures you can see the drive cable for the Tack going through the top of the padded dash in front of the passenger. Also if you look at the tack you can see the spacer ring around it. I will get pictures of the Jones tack and drive in a few more days.

Mike

[sithot]

Ahhh. Jones-Motrola. Hadn't heard those words in years. Cool stuff from "the day".

Tom

[Chuck Miller]

Raj,

From 4:15 to about 4:20 ...... there's nothing like'm .......
...... The whole clip ain't too bad either.........

http://www.youtube.com/watch?v=cADL_gjDim4


Cheers... and I hope you can make it work.....

[mike curnow]

Raj
Iam back with pictures.One picture is the VDO/Porsche 10000 RPM chronometric tack front and rear with the piece that bolts to the end of the cam, and the right angle drive that bolts to the end of the cam housing.The Jones/motorla pictures are the tack, and the drive. The VDO tack is1-4 and is Chronometric, one Jones tack is 1-4, my other is1-2. The one that has the 1-2 ratio says Jones on the face, the 1-4 says Jones Motorla. Do not know if that is significent as far as ratio goes. I have not taken either of the Jones tacks apart so I don't know if they are Chronometric, or Magnetic drive?I don't have the aluminum box like you have, I guess its the RPM interruptor? Are their wires going to it? I also don't have a right angle drive for the head like you are showing. Do you know if jones were Chronometric?

Mike

[sithot]

Vintage (pre-1969 /2 and earlier) BMW bikes also used a cam driven tachometer drive. The ratio off the cam was 1:4. Pre-65 bikes all had to be cam driven as the oil pump gear was not accessible. Off the oil pump it was 1:2. The oil pump arrangement is a bit cumbersome but effective. The oil pump drives are being reproduced.

Man your stuff is COMPLICATED! But you knew that, didn't you?

Tom

[mike curnow]

I know I posted pictures but they seemed to have disappeared? I will try again. As far as RPM disrupters go the 1967 S had a disrupter built into the distributor rotor, activated by centrificle force.

Raj
What car are you going to put the Jones Tack in?

[sithot]

Thanks to Robert Bosch. The T had its own, the E had its own and the S had its own. I've got some old S rotors somewhere. The cut out is marked on the bottom at 7,300. Had a silly spring with a tab that grounded out the distributor once the centrifugal force. Hopefully the springs were "correctly weighted"!
These are not nearly as sexy as an electronic setup but quite effective. Ever heard anyone at an autocross bump into it? Sounds like a stutter box on a drag bike or car at "the tree".