Sire

And if you're really smart you rebuild it allso.

pantera43

My car only had 38,000 miles on it. While changing out the caps and rotors I went to place on the rotor on the secondary distributor and "felt a sudden jerk" and the rotor spun ! The belt wasn't frayed but appeared more like cracked. As suggested by "dfinnegan" I disconnected the igniter to that distributor. The car still started up and you would not have noticed the car had a broken belt. Just the slightest loss of power.Thank god I caught it in the driveway....

Dan

demonfish

its on my list - new belt waiting!

Livefreeandrive

The piston powered pilots on this forum know about the power decrease as we do a "mag" check on our engine running preflight ground check. We switch one magnito off at a time and watch for an rpm drop as modern piston engines are dual plugged. If I was driving a car I wonder if I would sense losing 6 spark plugs? I realize that aviation engines are engineered to provide peak torque at lower rpms thaan cars. I fly piston helicopters and you feel every bit of power change.
Does anybody have pictures of before and after this vent kit. I am new to my car and this issue really concerns me. I plan to replace the belt for piece of mind and please pardon me if I overlooked this item in the 964 DIY section.
Thanks,
Steve

Indycam

"What pin are you talking about?"
There is a pin , a tapered pin , that gets taken out .
To take the pin out makes the old pin worthless .
The new pin gets peened .

The pin is iirc about $1.

Indycam

The vent kit is a tube and a plastic clip / adapter .
It hooks into the side of the distributor body .

https://rennlist.com/forums/964-foru...w-to-tell.html

demonfish

should we vent this pipe out thru a 6 foot tube extending out the rear deck in some attempt to fill the hole in the ozone layer?

Steve Weiner-Rennsport Systems

You sure will,....

Early RSR's ('73-'75) had two dash-mounted switches for each ignition control unit for the very same purpose.

amr89c4

My 89, purchased 2 years ago, had 42K on the clock and original everything, including the distributor belt and lack of a vent kit. I bought the parts from Pelican and installed myself.

As Steve noted, there is an obvious RPM drop when switching mags. I see no reason why one wouldn't see the same in these cars at say 1700 as in a runup check in a 72.

I'm thinking a mag switch would be a worthwhile, not to mention cool, upgrade is in order. Should be easy enough to add. Left-Both-Right

The reason some people have not noticed a broken belt is the because if the rotor stops between two cap contacts you don't get a out of time spark. Other folks may be unfortunate in that for various reasons they either can't feel or hear the difference. Some people have an ear and butt for that kind of thing and some don't.

If the rotor lands on a cap post, it won't take long for some serious damage to occurr. Listening to the sweet sound of that engine and getting used to how it sounds will pay higher dividends than listening to your tunes.

ThomasC2

I changed my belt last year. The old one looked OK but it was much stiffer/drier than the new one. It's good to know that it is replaced!

stevebozzy

because this is an electrical problem ( after belt has snapped)
is there anyway of connecting a warning light to the ignition to let you know if its broke ?
i will get my belt checked / replaced at the next service.
steve

Indycam

"is there anyway of connecting a warning light"
Two of the new led timing lights hooked into each of the distributors , four leds in all .
If all four are "on" then the two rotors are spinning .
http://www.jegs.com/p/Proform/761701/10002/-1

markc123

I'm with you Steve, 60K is the time to do it.. There is no Rhyme nor Reason as to when these belts break. I have been replacing belts on these distributors for over 10 years now and I have seen broken belts at 30K and belts that look fine at 130K so as peventative maintenance I agree with Steve.. Replace the belt at 60K

Mark Cohen

Lorenfb

"The question of potential damage depends on where the lower rotor comes to rest after the belt snaps."

Actually, a stopped rotor can cause cylinder damage irrespective of where it
stops rotating. Given the voltage of the spark and the size of the rotor tip,
the spark will most likely jump to either cylinder's distributor post at a rate
six times the normal rate, i.e. a spark every 120 degrees of crank rotation.
So, it's possibile that two cylinders could be damaged over a long term neglect
of the problem.

Remember, this type of electronic ignition with a distributor has timing problems,
i.e. The distributor rotor must "follow" the advance curve. If it doesn't, the spark
will jump to either of two adjacent cylinders.

To avoid this problem, Porsche should have placed the Hall Sensor on the
other distributor. Then a failure of the belt would have caused a Hall Sensor
CEL.

boxsey911

This is one of those threads that makes me nervous because I don't know what shape mine's in.

Fancy doing them in tandem Matt?