Is there an easy way to check distributor drive belt on a 964?

I know there have been various discussions relating to this but was wondering if there is an easy way to evaluate the condition of this belt. My car runs great but I've heard that it can run just fine with a broken distributor belt.

My car has the vent kit (I believe it came with the car new as it is a 94 that was built in 8/93) so I'm probably concerned over nothing. On the other hand, it's 7 1/2 years old and has 50K on the clock, and most rubber belts should be replaced periodically.

So, is there an easy way to have a look-see?

Thanks,
Mike 94 C2 cab

If you have an inductive timing light just check if the bottom and top plug have the same timing.
Otherwise remove the dist. caps and check the rotors.

Why not just remove coil wire from each distributor and try to start car with upper plugs, then lower plugs. Should be able to run off each independent distributor. Removing cap seems like alot of work. This test should also show you if coils and plugs are in good shape.

Not an easy way to have a "look-see". I suppose you could pull off one of the "inspection" plugs (your vent is plugged into one of them) but you would have to know what you're looking at...and who knows...maybe nothing can really be seen from them.

Considering the age an performance of the car, I wouldn't worry about it. The newer cars are supposed to have better belts.

Good Luck,

Bill Wagner

Thanks! I like the idea of disconnecting each coil and starting the car.

But. . .I also noticed that there is a wire harness that connects to the fan-belt sensor (a wheel that rides on fan-belt which activates a dash light if the belt breaks). There is another electric connector attached to the distributor, right near the vent hose. The wire from this connector ties into the same wire harness as the fan-belt sensor. Very suspicious! Could there be a sensor on the distributor belt also?

If I remember, when I get home I'll take a photo and post it here.

Thanks,
Mike 94 C2 cab

I don't think the second wire connection on the dist. ties into the belt. When my belt was blown - no lights or anything.

I also used the disconnect method to start the car off of only the upper or lower dist. Worked like a charm.

Pull the caps and try to turn the left rotor. If it spins freely, belt's kaput.

When you disconnect coil, don't let engine run for a long time. Just let it start up. If engine starts on each cap, you questions are answered.

pull the plug from each ignition module, one at a time, while the engine is running. they're on the left side of the engine compartment. pulling the coil wire can damage the fragile ignition electronics. if the belt is broken, leave the module for the belt driven distributor unplugged if you have to drive the car before it's fixed. that way there isn't a constant spark to whatever wire the rotor happens to be stopped at. it also won't fight the starter.

Thanks for the excellent advice. I unplugged each ignition module while the car was idling (very easy to do). Each time, the idle would drop and roughen. . .equally for each side (top and bottom). This tells me that all is OK.

Nothing like peace of mind.

Thanks again,
Mike 94 C2 cab

>> My car runs great but I've heard that it can run just fine with a broken distributor belt<<
WHOA !! I have first hand experience with this. We were at Roebling Road two summers ago when my cousins C4 started running rough and popping at times. The higher the RPM'S the worse it got. Well we looked and checked things, couldn't quite figure it out, that is until it blew a hole in the side of the head. The long and short of it was the dist belt broke and the rotor stopped on number 4 cylinder. After several laps at max RPM with the same cylinder firing every time the coil fired, it basically melted the piston and cylinder. $9,072.00 later, 72.00 for the belt and $800.00 for the Uhaul and trailer to get back home. And the most ironic thing about the whole situation, was someone had left a Haynes manual for a 911 inside the Uhaul !! It was very weird!

rattlsnak:

So ***YOU'RE*** the guy that it happened to!! I've heard you're story...it's sort of an infamous (rare...but not alone) story of the distributor belt breaking.

In *MOST* cases when a distributor belt breaks, the secondary distributor wiper "settles" far enough away from a contact that all the driver experiences is either nothing more than a slight loss of power, which may not even be noticeable to someone who doesn't push the car, to erratic performance (knocking, pinging, obvious loss of power etc...in which case the wiper is close enough to provide an erratic and inconsistent spark). In cases where the owner doesn't push the car and the wiper simply isn't allowing the car secondary distributor to fire at all, this problem can go undetected for a long period (like years!). You're case can happen, but it's relatively rare for a wiper to settle right on top of a contact or close enough that it's firing all the time. This, however, doesn't mean *ANYONE* should assume their car is OK if it starts acting up. If it's me, and I start developing symptoms that could even remotely imply a distributor belt failure, I'll tow the car home and troubleshoot it....with the belt being suspect #1.

I guess the moral of the story here is that if your 964 starts acting up (pinging, backfiring, extreme loss of power, severe stumbling...what else can I add?) an owner might be well advised to ASSUME the distributor belt has broken and get the car towed in for servicing (or service it themselves if they know how) rather than risking a $9K rebuild.

At this point, I'm editing this post. I'm an electrical engineer. It seems to me that if a set of sensors were put on each of the spark plug wires on the secondary disptributor, and it was detected that the firing order was inappropriate (i.e. no spark, erratic spark, or spark firing on one cylinder), a circuit could be designed to disable (probably with great ease) the power to the secondary.

Any thoughts, anyone???

Bill Wagner

[This message has been edited by Bill Wagner (edited 05-23-2001).]

It seems that at the very least, if you get the standard set of symptopms, you could do the ignition module wire-pull test to determine if the problem is caused by a broken distibutor belt, and then disable the belt driven one to avoid blowing a hole in the head.

This way, I even assume you could drive the car home on the promary distributor?

------------------
Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net

Hello

Standard service routine every time you change the spark plugs is to check the distributor parts and the complete ignition.

Normaly those caps do have some 80 000 km change intervall but sometimes they need to be replaced sooner.

If you remove them then you can see if the TDC marks are pointet.

Worn Caps and finger get a wider gap witch leads to a higher spark that leads to ozone with leads to rubber belt failures.

So everything starts with a simple part that didn´t recived attention.

The "fix" is to vent the distributor and so the ozon will be away.

Making a ozone resistent belt would have to be paied with shorter lifespann and more frequent belt renewals. ( Well you can imagen what the typical costumer would say if that belt has to be replaced every 100 000 km - Poor design )


Yes Porsche could have used two hall sensor pick ups and compared there signals or just a simple ifra red diode that counts the reflection from a small mirror on the shaft. They also could have used a chain or gears.

Well KISS was in ther eyes.


The engine will run on the importent one ( the direct driven ) circuit without bigger problems. The DME will adopt to it and you will loose some power.

But keep in mind that the engine was constructet for dual ignition use and has a very high compression rate.

Also the expensive failures happend when the engine was reving on high level. If the belt then broke the loose distributor spinned on for several secounds geting unsyncronized and wrong fireing.

Some belts just lost some tooth geting retarted and generate more ozone that killed the belt later......

Grüsse

Bill, I'm wide-eyed here! I cant believe that story got out!! There were not that many people there! It wasn't a PCA event, it was a closed/private testing day! Gee, I'll have to tell my cousin he is a celebrity now!

[rbogh901]

Originally Posted by john walker's workshop

pull the plug from each ignition module, one at a time, while the engine is running. they're on the left side of the engine compartment. pulling the coil wire can damage the fragile ignition electronics. if the belt is broken, leave the module for the belt driven distributor unplugged if you have to drive the car before it's fixed. that way there isn't a constant spark to whatever wire the rotor happens to be stopped at. it also won't fight the starter.

Old post, still pertinent topic. Can someone please post photos of the plugs on the ignition modules for those of us who appreciate guidance as opposed to "personal experience"?


Thanks, especially to John Walker.

[ischmitz]

The ignitor modules are mounted on the metal bracket that holds the twin coils in place. There are rubber-booted connectors going to each of these black modules. Unplug one at a time. Every time you unplug one you should feel a sligth change in the idle but the engine will keep running. If it shuts down you pretty much have indentified that only one channel (the one you unplugged) was working. Chances are that either the distributor belt has snapped or the coil or ignitor are broken.

Ingo

[rbogh901]

thx Ingo.

yes, if the motor stops I plug that one back in and unplug the other one until repaired. this prevents damage from the stationary distributor.

do I have to be concerned about voltage or shorting when I pull them off with the engine running?

I guess the only one that needs to be unplugged is the one corresponding to the primary/master distributor since it isn't the belt dependent one. that leaves the ignition solely to the slave distributor.

[ischmitz]

You can safely unplug the low-voltage connector to the ignitor while the engine is running. If you find that one of the channels isn't working you definetly want to track that down and repair it.

While the car will run on one channel only you will get much more detontation and that'll stress and crack your rings. A lot of engines got destroyed because of that.

I would unplug both so you also detect the case where only the secondary is working. You could have a healthy belt while the primary ignitor is dead.

Ingo

[wayner]

A British magazine ran a story of how a broken belt at speed caused a snapped crank shaft when two different sparks and cylinders fought each other!