1969S Fuel Injection Linkage Rods. (Lengths)

[Nickm]

I've gotten a few questions answered so quickly when I searched the forum and couldn't find any info.
I have one of those questions again...
Doing the final tune up on a '69S, after taking so much time and ordering so many parts to make it
run and look like new. Fortunately the car ran pretty spectacular before it's restoration... but now I
want to have it dialed in perfectly. Does anyone know the exact lengths of the connecting rods for the
fuel injection? My mechanic told me (before I bring it to him, to make sure the rods are all to the
factory specified lengths before bringing the car to him (as they were all disassembled with new rod
ends etc...) If we start out with the rods at the correct lengths, that will save him quite a bit of time,
to start dialing them in.
Does anyone know the factory specifications for the rod lengths? It saves him from taking them all
off and adjusting them then reinstalling them...
A BIG pre-thanks!!! ;o)
Nick

[911MRP]

Hi Nick,

From memory for MFI ...

the critical one to get right by measurement is the rod between the pump regulator lever and the cross shaft -- 114 plus or minus 0.2 mm centre ball to centre ball

Once right others are adjusted to be free of tension and or pressure -- obviously things must be correct on the idling stops
The rods left to right might actually have a difference -- 5mm max.

Suggest you and your mechanic get the CMA document and then do it by the book ...following right steps right sequence... there is great info in it that goes way beyond rod length adjustment and correlation that is just one of many steps, also document will confirm my fallible memory.

For reasons explained not sure there is a factory specification for them beyond the one of 114? You can get them close if that is what they mean?

Open to be corrected on any of this from those who do this MFI procedure regularly for a living.


HTH

Steve

(Have you / they got protractors - certainly not essential, but cool items I picked up a original set not repro from a 40 year in trade retiring guy)

[edmayo]

You are dead nuts correct Steve, the pump control rod must be 114 mm center to center. You measure that by measuring diameter of of one socket end, then subtract that from total over all length. That results in center to center length. Disconnect all other rods from the crossbar and then install the pump rod. NOW all other link rods are are adjusted to just snap on without any pretension. This is the important step that so many fail to do. Porsche stopped requiring the use of protractors sometime in 73 or 74.

[Nickm]

Awesome! Makes 100% sense. You guys are great!!

[bliebler]

You are dead nuts correct Steve, the pump control rod must be 114 mm center to center. You measure that by measuring diameter of of one socket end, then subtract that from total over all length. That results in center to center length. Disconnect all other rods from the crossbar and then install the pump rod. NOW all other link rods are are adjusted to just snap on without any pretension. This is the important step that so many fail to do. Porsche stopped requiring the use of protractors sometime in 73 or 74.

Ed,
The procedure for measuring the pump control rod that you mentioned above, from the MFI Manual, may not apply if the socket ends are replaced with the later style ones which have flat ends as opposed to a rounded end. The change from the orig rounded end socket to the flat end is over 1mm.

[edmayo]

Good point, something else to watch out for. Did you make a fixture to snap the rod onto? May be time to make one anyway.

[bliebler]

Ed,
I thought of that but what I did was: measure what one turn of the socket changes the length of the rod which is .8 mm. I then measured the cup hole of the socket which is 8mm.

I got an estimate of 114mm with the cups opposed to each as when connected to the pump.
I then opened the socket so both cups face up (holes facing up). I measured the inside of cups and figured that 1/2 of the cup hole is 4mm and 1/2 of spinning the cup is .4mm and then got it close to 114 which mine was a little over that but if I turned in down it was under so I went with the larger which was about 114.3..

[edmayo]

As long as you are 114 . Something you are okay. It's the ones that come in 2 mm off that cause real problems!

[911MRP]

Ed,
Any credit for me knowing anything about these old MFI cars frankly all goes to my friend -- one of the longest established independent Porsche specialists here in London/the UK -- Chris Turner. A very patient teacher. I can now claim to know maybe one millionth of what he knows

S

[bliebler]

Ed,
I went on the high side of the 114 measurement because of some slop in sockets and cross shaft.