964/993 Distributor Belts
Picked this car up from a customer to inspect and get into top running shape. As soon as I loaded the car in 3rd gear, I could hear and feel the detonation happening in the engine, so I was pretty sure I knew what that was going to be.
First thing to do when I got home was to check out the airbag light. Looks like a crash sensor was throwing an error, so I cleared the code and it stayed off. We will see if it comes back on.
Putting it in the air, lots of oil leaks which are typical in 964’s. Valve cover gaskets, timing chain gaskets, oil thermostat gaskets are all prone to leaking.
The 964 and 993 naturally aspirated models use a twin plug distributor system, meaning 2 banks of 6 plugs. The 2nd distributor rotor is run off a ribbed belt via the main distributor shaft. This rubber belt has a finite lifespan, and will break eventually. The problem when it breaks is that the 2nd rotor will stop in one position, usually firing on a cylinder constantly, causing detonation in that cylinder. By removing the 2nd cap, you can grab the rotor and try and spin it. If it spins, uh oh.
Inside you can make out the ribbed belt is frayed and broken. This means the distributor will need to be pulled, and I will rebuild the unit. I recommend a new belt every 60k miles. Failing can cause serious engine damage due to lean condition/detonation.
You can see the rotor is cooked from constantly firing on one cylinder.
And the wee tiny belt removed. I’ll get the parts ordered and we will start on this project next week.