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DIY - 964/993 Distributor unit rebuild - Change belt/bearing/caps/rotors.

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MarkGolf
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MarkGolf PCGB Member
2020/08/20 13:56:39 (permalink)

DIY - 964/993 Distributor unit rebuild - Change belt/bearing/caps/rotors.

Hi Everyone,
 
I wanted to share a DIY of refurbishing the twin distributor setup on my 964. I recently did this job due to a misfire. I thought, while I am changing the rotor arms and distributor caps, I may as well refresh the distributor. Nice to have piece of mind that a critical part is in top order.
 
This applies to the 964 Carrera and RS.
 
A small overview, the ignition system on your M64 engine is made up of 2 coils, 2 distributor caps, 2 rotor arms, 2 main sets of ignition leads + 2 coil links and 12 spark plugs. Each cylinder in the engine has 2 spark plugs and each coil/cap/rotor is responsible for supplying spark to 6 plugs. This may sound confusing but each pairing of plugs is fired up at the same time, totally synchronised by the distributors, this is done by taking drive from the engine, through the primary drive shaft (long one) and the drive is shared to a secondary shaft (short one) via a small rubber belt. This is a service item, often forgotten about or overlooked.
 
It has been known for this small rubber drive belt to perish and snap, causing havoc. In the early days, it was noted that moisture used to build up in the belt chamber, so Porsche introduced a vent kit, see image below;
 
Part number 000 043 202 52

 
A simple pipe which went from the heater blower pipe to the distributor housing. Your 964 should have this if it does not already. 
 
Being a rubber belt, it is a consumable and must be changed. The distributor housing is also made up of 4 bearings. 
 
So, while changing the belt, you may want to inspect your bearings for play. If you detect any play, you will need these parts;
 

 
You can go overboard with new allen bolts which hold the housing together but there really is no need for those unless you damage your own. 
 
If you wish to refresh your rotor arms and caps, part numbers below.
 
Rotor arm - 930 602 902 02 x 2
Distributor Cap - 930 602 919 01 x 2
 
What it all looks like
 

 
Tools;
13mm socket
Philips screwdriver
Flat head (for levering)
Gear puller (optional)
Rubber mallet
Mallet
Punch
Allen set
 
To remove,
 
Firstly, set your engine to TDC. Rotate the engine clockwise, I used my hands on the fan to turn it over, but you can use the bolt on the pulley. Look for the Z1 timing mark on the crank pulley, a little notch.
 

 

 
Remove caps with leads still attached. Upon refitting the distributor housing, it makes sense to fit the new caps (if changing) at the very end after ensuring your alignment is ok and you can swap the leads over 1 by 1 to reduce risk of messing the order up. You just need a Philips screwdriver to remove the 4 screws holding the 2 caps on. It can be fiddly as the leads are a bit tight, I undid the cowling over the fan to give some more slack.
 
Unplug the electrical connector and vent kit.
 
Rotor arms should point to the small nipples on the housing once timed correctly, it is important this position is held when refitted to engine. If it is not, the car will not fire up, therefore, you will need to remove the distributor unit and realign the engine and rotor arms. It is easy to get the timing wrong as the crank can turn over 2 times for every full rotation of the engine.
 

 
Once aligned, remove the 13mm bolt holding the distributor unit in place, a few taps with a rubber mallet may be required.
 

 
Remove rotors and dust caps
 
The first main thing I did was remove the pin holding the drive gear, some people drill this out, I tapped it out as I just had a hollow metal roll pin as opposed to the solid pieces I have seen. If yours is solid, I wouldn’t tap it out as you may end up ballooning the top end out, making it harder to tap out.
 

 
Next, pull the gear off, mine came right off but a pulley may be required.
 

 
You MUST keep track of the washers and maintain the order they are in.
 
This is a great reference. The only thing to watch out for is that some washers are thicker than others, I have no idea if the orientation makes a difference, but it is best to retain the order they are removed in.
 

 
Next up, remove the electric connector, lever clip off
 

 
Pull plug socket out. Poke any wires back into the unit.
 
Now you need to remove 3 philips screws from the top and pull shaft up.
 
You should not spot 5 allen head bolts, undo these to access the belt.
 
You can now manoeuvre the old belt out and new one in.
 

 
If this is all you wanted to do, simply follow these steps backwards to reassemble, if you wish to change bearings, carry on reading.
 
Remove the zinc plated protective cap from the base of the secondary shaft, you can tap/lever this out with a pick tool or small screwdriver.

Clean any grease away and undo the retaining cir clip
 

 
Inspect your bearings, they may be fine, no play, if you can wiggle them, they are on the way out. Some people pull them apart from re-grease. That was not an option for me.
 
Bearing removal was slightly tricky, I essentially set my distributor unit up on my workbench, sometimes in my vice and hammered away using a socket and a punch to evenly knock them out. I found that removing the inner bearing sleeved helped give access to each bearing when knocking them out. Nothing to really picture here, it came down to using anything available to get the bearings out, it wasn’t too pretty.
 
 
I didn’t change the bearing which is at the bottom of the primary shaft, I could not work out how to remove it.
 
For the 3 main bearings, I used the old bearing races to press in the new ones in my vice, this was straight forward.
 
At this stage, it is now a case of rebuilding!
 
Slide your shafts back in ensuring the belt is around the primary shaft and sit the belt in the housing. Now you need to fiddle with the secondary shaft and ensure you align the shaft correctly. There are 2 small nipples on the distributor housing, fit the rotors to help line the shafts.
 
You then need to squeeze the primary shaft in so that you can get the washers and drive gear back on and new pin in. I used a valve compressor but some people have used body weight. I lightly tapped my retaining pin back in. Remove clamp.
Make sure to mushroom the ends of the pin to avoid it coming out.
 
Feed wires out of the house and refit plug/retaining clip.
 
Refit secondary shaft and use new cir clip to retain shaft in place. This was a very tight fit.
 
Refit dust caps, 2 plastic ones on top and zinc one on bottom
 
Ensure the rotors line up to the nipples on the housing
 

 
Your distributor housing is now ready to fit back into the car, slowly line up and fit to the engine, ensuring the rotors hold their aligned position, once in, fit and tighten 13mm nut.
 
Fit caps, ensure all leads are correctly fitted.
 
Attempt starting the car, if it fires up, success, if it doesn’t recheck aligned of engine and rotors.
 

 
I noticed a smoother feeling car with the new caps and rotors, I had previously changed my leads and spark plugs also, so next on my list is new coils, then my ignition system is fully refreshed.
 
You can now refit any parts you removed to help with access, belt tensioner, heater pipe etc and get ready for a great drive
 

 
I hope this helps, any questions or if I have missed anything, please let me know!  I will add more detail and pictures as I piece them together.
 
Thanks,
Mark
post edited by MarkGolf - 2020/08/20 14:18:47

Current fleet
1991 964 Carrera
2005 997 Carrera S
2008 957 Cayenne GTS
2003 Boxster 2.7
1994 Eunos Roadster S Special Turbo 270bhp!
1991 Mercedes 500SL
1979 Mercedes 280e
1995 VW Golf VR6 3.0

1 Reply

Hacki
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Hacki Guest of the Club
Re: DIY - 964/993 Distributor unit rebuild - Change belt/bearing/caps/rotors. 2020/08/20 16:44:32 (permalink)
Mark,
 
well done and thanks for sharing this job in detail and so well explained. It´s in fact important to check that rubber belt on a regular basis as it can cause serious damage once it breaks. And yes, the distributor has to be vented with that kit shown above.
To do this overhaul might be a tad beyond DIY for mere mortals, but can be done with the right tools, some experience and a good feel for what you´re doing. I leave it to a specialist.
 
The leads can also be an issue - when I sensed a lack of power (which you won´t feel on the roads inside the legal limits) it turned out that the lower set of leads was cooked and there where sparks everywhere inside the engine bay but not at the plugs. So it ran on the upper leads and plugs only and that felt like 50 horse less. Leads replaced and there she was as usual! Well worth a check.
 
How old was / how many miles had your distributor on the clock when you refreshed it?
 
Keep up the good work!
 
Hacki
 
Current fleet:
1990 964 Cup
1995 993 Cab
1964 Volvo 544
1970 Mercedes 200
1976 Ford F 100 XLT Ranger 390 cui
1991 Volvo 245
1991 Volvo 960
1992 Yamaha Warrior
1998 Volvo 940
 
 
 

Owner of an inflatable Spitfire and an escape glider
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