Here is a recent summary post on the distributor belt issue by Adrian Streather from the Rennlist 964 Forum dated 11 November 2001.
Dear Bob,
The only reason I am writing this again is because my original description of
the problem after a lot of research has been lost to the board.
The distributor belt "problem" is not "now" a 964 problem, it is a "Care
and Maintenance" issue. The original secondary distributor design had a flaw.
Ozone build up in the distributor caused premature aging of the belt and it
broke. Porsche picked this up fairly quickly and designed a fix which works.
They vented the secondary distributor. Less than $US20:00 for the parts.
Unfortunately in places like the USA, Technical Service Bulletins were not
carried out under warranty by Porsche dealers and the independents generally had
no idea anyway at the time. I agree that Porsche communications of problems or
issues was not brilliant and at best was inconsistent. Here in Europe (except
UK) carry out TSBs was and is standard. In Switzerland, a requirement of the
law. There were warranty provisions in all of these TSBs as well.
Many 964 owners were totally unaware of this issue. I only ever took issue with
the big drama being made of the problem which is really an owners, national
dealer politics and costs and a lack of knowledge problem rather than a "964"
problem. I agree it started as a design flaw.
Anyway back to the story. Porsche introduced into the maintenance schedule, a check of the ignition system. A full functional check should be carried out every 12,000 miles. In my book I expand and explain this more fully. ANY RUBBER BELT fitted in ANY AUTO should be replaced every five years or 100,000klm regardless. Various repair places around the world I have contacted recommend from various intervals. I recommend 48,000 miles because it co-incides with a service interval or every five years.
The other issue I took up was how could you tell your belt was broken. The consensus from around the world was, most people couldn't tell the difference. In my book I have written up a couple of things a 964 owner can do to at least see if there may be a problem, in between the service intervals.
 | If there is no vent kit installed in your 964, install one immediately and replace the belt now!. |
| If you have no idea when the belt was last changed, replace it now!. |
| If the belt can be traced to last change calculate 48-50,000 miles for the next change or five years whichever comes first. |
| Ensure at your next servicing whether you do it yourself or have it done, the belt must be checked. |
| If in any doubt at all, replace the belt!. |
| Steve Weiner has a service for this and if you are down for the winter this would be a good time to do it. The belt can be changed in your garage but I only recommend this for the experienced DIY. I must also point out that you need to find a repair facility with experience to do this as well. |
Finally the potential damage. Yes it can damage your engine, eventually!! if you are really unlucky or it is not your day. If you are racing or in any way pushing your 964 hard, consistently I recommend you check the belt before each race or event. This should be common practice for the professionals. I never hurts to be conservative but do not get paranoid over such things, it is a waste of energy. Look after the 964, follow the maintenance procedures. For all US based 964 owners I highly recommend that you check out www.alldata.com. Download the free list of TSBs for your model and check through your records to see which ones, if any have been carried out.
Ciao,
Adrian
911C4
PS: From the data I have collected around the world, from many repair facilities
including across the USA, the most common reasons for engine rebuilding are, oil
leaks, lack of oil, engine overreving and engine over temp. I have two that were
in for holes in top of pistons, blamed on a broken distributor belt, both were
racers. I have yet to be handed evidence that a normal daily driver 964 has
suffered catastrophic engine damage before the belt failure was picked up. If
somebody has this evidence I would love to get a copy of it.
