964 - Distributor Belt Procedure

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If you are reading this you have probably already determined that the distributor belt which turns the secondary distributor sprocket via the primary distributor sprocket is broken. If you are lucky, when the belt broke you noticed a lack of engine power in general but most notibally when under load/going up hill, rough idle & pinging.

If you were unlucky, not only would you have observed the above symptoms, you may have also damaged a cylinder or two. If the rotor of the secondary distributor happened to stop dead on a discharge contact for one of the cylinder spark plugs then the damage, if the problem was left undetected for some time, could indeed be catostrophic (burn from continual detonation from one cylinder to the next is possible).

Now if you are still unsure as to whether the belt is broken or not follow one or both of these procedures; 1) remove the leed from the coil for the primary distributor---the car should start running only on the secondary distributor if the belt is unbroken---if not the belt is likely broken. AND/OR 2) (*see Step 1)with both caps off turn the motor clockwise from the fan bolt or as I did, by hand, grabbing the fan blades and turning. You should see the primary distributor rotor button turning and if the belt is broken the secondary distributor rotor (*see step 1)button will not turn. If you have established that you indeed do have a broken distributor belt then turn on your favourite music & please read on........


Step 1. Put the distributor cap back on & give the area around above & below the distibutors a good clean to ensure no rubbish/grit could fall into the assembly or the hole from where you will soon be extracting the primary distributor shaft. It may help to remove the heater blower motor and associated plastic ducting, this should give you a bit more space to work in. (*)Now, if at all possible, it would be a very good idea to have checked to see where the rotor of the secondary distributor had stopped after removing the secondary distributor cap. This may clear any doubt as to whether there is cylinder damage. You won't be able to see the belt at this stage with either cap off.

Step 2. When removing the distributor caps be sure to mark the leads so you know exactly where they all go back. At this point you must take care to ensure the rotor buttons are NOT removed until you are sure the engine is at rest on top dead centre (tdc) of cylinder #1, . If you are at tdc#1 then the Z1 indicator mark on the main belt pulley will line up with the coresponding mark on the fan housing, as well as this the rotor button for the primary distributor must line up with the small protruding notch on the distributor outer housing, if the belt was unbroken the secondary distributor rotor button would also be pointing at the protruding notch on its distributor housing . Now if you are confused because the Z1 mark on the pulley is lined up but the primary rotor button is not pointing to the notch you are most likely pointing at cylinder #4---just keep turning the pulley clockwise one more combustion cycle until Z1 comes around a second time, this should now see the rotor button lining up with the notch (it may be aiming just slightly to the left of the notch).

Step 3. Remember to keep all components in the order they come off in so they can be put back exactly how they were. Remove the rotor buttons and dust shields, you should be able to glimpse parts of the offending belt now. Remove the vent pipe from the housing. The distributor assembly is held down with one 13mm nut & washer--remove these and try pulling the assembly out using just your hands. You may encounter some resistance due to the vaccum that builds up from the seal around the shaft, some people experience a lot of resistance, if you do then take care if levering or pushing out from below to not damage the distrbutor casing.

Step 4. Having succesfully removed the twin distributor assembly, you now have a choice--to send it off to a mechanic who can overhaul it for you, or you can pull the assembly apart yourself & assess what needs to be done to get your car back on the road & have a go yourself--remember, 'those hours your porsche spends off the road...you can't get them back!!!' I have overhauled my distributor having previously never pulled apart a distributor before and I believe most people with a decent understanding of things mechanical will have success at changing the belt & getting there car back on the road. I replaced the belt, drive shaft pin, shaft seal, removed any traces of corrosion, lubricated the shaft and mechanisms in the distributor and I decided to change the bearings on the primary distributor as well while I had the unit in pieces. If you have no experience in replacing bearings I would not recomend you change these....however, if they do not turn freely on the shaft, they must be replaced. Get somebody with the required experience to perform the bearing replacement task if it is not comfortably within the scope of your skills, there are some specialist tools/skills required and it is easy to damage the bearing housing if you are not competent with this aspect of the repair. As a side note I found Porsche did not supply these bearings through my parts supplier & I had a tough time tracking them down--the first 7201 angular bearings I purchased had slightly (0.44mm) smaller internal shaft bore--so beware!! At the end of the primary shaft is the drive gear which is held onto the shaft with a mild steel pin. The genuine replacement pin I got from my porsche parts supplier appeared to be made chiefly from copper and easily mushroomed, as required, when tapped down on both ends upon installation at the re-assembly stage. To get the existing pin out you will need to hold the shaft dead still in a vice and drill the whole pin out dead straight (don't bother trying to save it), a drill press would probably be a better idea if you have access to one. Some people have experienced pressure releasing when the pin is removed--take care to not lose the washers from the base of the shaft or the order they are in.

Step 5 The black connector plug at the side of the primary distributor housing has to be dismantled to the point that the white connector plug which resides inside the black outer plug socket can be pushed into the distributor housing far enough to enable the withdrawl of the primary shaft with components attached. To do this first remove the spring steel retaining clip from the inside wall of the housing, this is best done with long nose pliers and a slotted head screwdriver if leverage is required. Next pull the complete 3 pin connector plug out from the distributor housing (taking care to not damage or disconnect the three wires) and then remove the black outer socket off the small white 3 pin plug, the plug now can be pushed back into the housing slightly sideways to enable the withdrawl of the shaft. Remove the three phillips head screws from inside the primary distributor and withdrawl the shaft (more washers here!) taking note, and marking if necasary, the position of internal components in reference to the housing.

Step 6 To withdrawl the secondary shaft you will need to remove the metal (brass) cap at the base of the secondary housing. If you look close you will notice the 3 metal indents holding the cap into the housing, these will have to be filed down with a dremel or similar. Try not to damage the metal cap as you will need to put it back later, after deeling with the indents I used a small flat blade to prise the cap up gently working around the cap as I went. Behind this cap is grease, a circlip and more washers (check that order) mated to the lower 'open' bearing--note this bearing is different to the other three. Withdrawl the secondary shaft, next you need to seperate the halves of the distributor housing, one is on top of the other. First remove the 5 allen head bolts and then prise apart the housing halves with a flat blade, again gently & evenly working around the housing until they start to seperate, there are two small fixed pins which align the housing halves together and may cause some resistance to seperation at first.

Step 7 With the halves seperated you can remove any belt debris and clean the housing with very fine emery paper to remove any iregularities or corrosion. You should be able to check the operation of the four bearings now and make a decision as to whether they need replacing, at the very least they probably should be repacked with grease where possible (how do you repack a sealed bearing I hear you ask?) --- the answer is you really shouldn't, however, in my situation I couldn't get the correct bearings for several weeks so I had to clean, grease & reassemble the two bearings I damaged while pulling them off the primary shaft at the start of the job (this was before I found out how hard they were to get hold of). Place the lower or base half in a vice carefully and place the new belt into the base half and join the upper half back together with the base locking in the belt with the 5 allen key bolts. Insert the primary shaft back into the primary side of the housing carefully placing the toothed belt around the primary shaft belt sprocket, make sure the shaft is correctly alligned with the housing notch for tdc#1. You will not be able to insert the secondary shaft as easily and will need to remove the belt sprocket and washers from this shaft (check that order) and place them in the housing in correct order, the shaft has a keyway for the sprocket this should face pretty close to opposite the housing notch for tdc#1. You will probably need to try this several times to get correct alignment, remember both shaft rotor buttons need to point to there respective tdc#1 notches. If you are a keen fisherman you will probably find this step relatively easy, as patience is just what is needed, and a jar to collect the coins for every time you swear would probably need to be quite a large one!!

Step 8 Once you have the shafts back in place correctly get the three phillips head screws back in the primary disributor and make sure the three pin plug body is back out the housing opening ready for assembly, next you will need to get the spacer/washer/circlip components back onto the base of the secondary shaft--this is not easy as you need to get a clamp to slightly compress the components down the shaft enough to get that circlip back on properly, all without allowing the shaft to fall out of the housing. Put the re-lubricated brass cap back in place--I used a two part 'metal' putty to make sure the cap didn't come off later. Place the drive gear back onto the primary shaft and install the new retaining pin making sure to mushroom both ends of the pin to the shaft. Put the black outer casing back over the white inner 3 pin plug and reinstate this into the housing with the spring steel retaining clip. Check that turning the primary shaft also turns the secondary and that the rotor buttons aim to there corresponding tdc#1 notches, now you are ready to install the distributor back into the engine.

Step 9 As you insert the distributor back into the engine, the drive gear will want to turn slightly as it meshes back into the corresponding gear of the engine, you have to keep the rotor buttons ligned up with tdc#1 as well as the engine pulley at Z1. This procedure requires patience again and will probably need to be attempted more than once to get right. When achieved put the 13mm nut & washer back on and install the dust caps, rotor buttons & distributor caps. The small circles of felt under the rotor buttons in the top of each shaft should probably have a drop or two of oil added to them. Put the heater blower motor and associated plastic ductwork back together. Make sure all leads and vent pipes are correctly installed & start your engines!!!! Now, how does it sound to have all 12 spark plugs working---sweet! (to be continued, complete with photos)

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