924Board.org

stexch · Joined: 05 Dec 2003 Posts: 90 Location: Mankato, KS, USA

I was complaining to a friend that my '78 924NA cranks very slowly. He thinks that the problem is that there is a ground strap running to the aluminum cam cover. He suggests that if i move the ground to steel, e.g. the wheel well, I would get a better ground. Another friend said that this makes no difference. Any thoughts?

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

The cam cover studs are tiny, you need a larger gauge strap + eyelet connection! Not to mention that a stud going into aluminum won't conduct as well. I'm amazed it starts at all if this is your only grounding point from the battery?

I run one off the neg battery terminal to an intake mounting stud. And another from the neg terminal to the stock body location in the battery box. The intake stud is iron/steel and conducts directly to the iron block.
_________________
1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

stexch · Joined: 05 Dec 2003 Posts: 90 Location: Mankato, KS, USA

Thanks for the help! I'll make this change and let you know how it turns out.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

Use a set of jumper cables to make a temporary connection and see if that helps.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

leadfoot · Posted: Thu Mar 22, 2007 8:27 am Post subject:

Wouldn't running to the manifold stud actually be trying to conduct through an aluminium head???
I ran mine to the stud on the firewall and put a short link from there to the battery negative terminal. I also run another ground from the negative battery to the metal bracket that sits just in front of the windhield wiper motor...
leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

!tom · Posted: Thu Mar 22, 2007 8:46 am Post subject:

Aluminum is actually quite a good conductor. It's not much worse than copper, and is a better conductor than steel.

The problem with aluminum is that it oxidises, and the oxidised layer is an insulator. If you have a good electrical contact with the head, I can't imagine there being much of a problem conducting through the head bolts into the block. However, a block ground certainly wouldn't hurt, since it's the connections between conductors that tend to increase resistance.
_________________
78 924 NA
5-lug

stexch · Joined: 05 Dec 2003 Posts: 90 Location: Mankato, KS, USA

First, a correction of my original post. As near as I can tell, there are three ground straps:
1. Battery to aft side of intake;
2. Firewall to fore side of intake;
3. Cam cover to shock tower.

I disconnected the battery-intake connection and reconnected it on an unused shock tower bolt. My car now cranks more strongly.

a. There was a bare twisted wire that bolted to the same stud on the intake as the original battery connection. Is it necessary for this wire to be in contact with the one from the battery that I moved?
b . What useful purpose do connections 2&3 above serve?
c. There is a flying saucer shaped thing on my distributor, with a tube going nowhere. What is it?
d. Whatver happened to Timstar?

!tom · Posted: Fri Mar 23, 2007 4:21 am Post subject:

a) This bare twisted wire is likely an original ground. Exactly what parts are grounded isn't terribly important, as long as there are good grounds.
b) Those were multiple grounds, done to ensure that all components are grounded, and grounded well.
c) Sounds like your vaccuum advance. It's pretty important. That tube (if it's what I think it is) should be connected to your intake manifold in some manner.
d) He's still lurking I'm sure.
_________________
78 924 NA
5-lug

stexch · Joined: 05 Dec 2003 Posts: 90 Location: Mankato, KS, USA

Thanks for your response. Since I'm running Weber carbs, I assume that the vaccuum advance is not functional. Was this part of the emission control system, or was there some other purpose?

leadfoot · Posted: Fri Mar 23, 2007 10:18 am Post subject:

No, it was to advance the ignition to get better spark at high vaccum, some distributors cam with advance/retard... in addition to the mechanical advance bob weights built into the distributor...
The vaccum advance line was normally connected to the throttle body so that it only saw vaccum when the blades were open... IIRC

P.S sorry I was thinking magnetic properties for some strange reason....
Leadfoot
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Smoothie · Posted: Fri Mar 23, 2007 10:41 am Post subject:

Electricians use something like this on aluminium connections -
<click>

It's conductive + anti-oxidant.
I found it at the local hardware store for $3.89.
_________________
"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox