[shelby987]

This afternoon I replaced my plugs, wires, rotor, and distributor cap.....it was all pretty straight forward, it all goes together one way. I turned the key and the car started right up, idle felt much more solid than before, but I could hear a tick. I walked to the front of the car and could hear the tick more clearly......I put my hand on the distributor cap and could feel a pulse that matched the tick.....jumped in the car and shut the car off.



When I pulled the cap I could see that the rotor was making contact with the point at the 5 o'clock position as you look at the distributor from the front of the car. I pulled the rotor to make sure that everything had been seated correctly....it had, shims / spacers were installed correctly.....check the old cap.....SAME PROBLEM! Looks like the shop that last replaced this distributor cap ran into the same issue....I can only assume they just rev'd the snot out of the car until it made clearance?



I can't see any adjustment here, how do I get the centerline of the distributor cap lined up with the center line of the rotor? There is some corrosion on the face that the distributor cap sits on....but it locates on the OD of the raised circle, like a dowel, I don't know how to make this adjustment?



Just a point of referrence, this is a bosch cap and rotor. Is it safe to assume the .5mm of brass missing from the point means I already need a new cap? The rotor looks to be in better shape, it must be a harder brass alloy than the points?

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[MB968]

There are two castings that bolt to one another (with locating pins) and the rear one bolts to the head; the front one is the one the cap bolts to. These castings are supposed to keep the rotor which is bolted to the cam centered relative to the cap. The rear casting on my 968 was corroded such that the one locating pin was sloppy in it's mating pilot hole. My cap was badly cracked which is what led me to find the corroded casting. Take a look in this area.

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[shelby987]

So did you have to get a new casting to correct the alignment?

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[shelby987]

Upon closer inspection, it appears this is a problem a couple of people have come up with, I guess I will have to pull the top casting off and see what I have. Any good way to confirm concentricity between the rotor center line and the ID of the points in the cap before turning the key and listening for the tell-tale tap tap tap?

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[mbardeen]

Maybe manually turn the engine via the crankshaft? Should only take one or two revolutions to tell if you have contact.

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[shelby987]

I am thinking about making a ring with a lower ID the same as the distributor and the upper ID the same as the ID on the points....this way I could check clearance with a feeler gauge while turning the engine over.....this only make sense if I can actually adjust the case in anyway.....if there is no play, I am probably SOL and will need to buy new covers.



I am starting to wonder if I am looking at poor assembly following my recent timing belt replacement

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[MB968]

[quote name='shelby987' timestamp='1334756229' post='125455']

I am thinking about making a ring with a lower ID the same as the distributor and the upper ID the same as the ID on the points....this way I could check clearance with a feeler gauge while turning the engine over.....this only make sense if I can actually adjust the case in anyway.....if there is no play, I am probably SOL and will need to buy new covers.



I am starting to wonder if I am looking at poor assembly following my recent timing belt replacement

[/quote]



If you have an old cap, you could just cut the middle of the top of it out so you could see inside/use a feeler.



And, the inner casting shouldn't have been off for the timing belt replacement unless you replaced the cam seal. I haven't had mine off yet, but I'd assume it has a good fit on the head rendering it concentric to the cam bore. So, don't think you can screw this up. But, maybe there is some clearance that could be used to your advantage.



Finally to your above question, I did have to replace the casting because the pilot boss was just about completely gone due to corrosion. Hopefully this is not your issue, as the part was ~$950 from Sunset, higher from other sources.

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[shelby987]

Well, I now know the source of the problem, when I got the two front covers off, it was painfully obvious! Both of the cast bosses (one being the locating hole, the other a mounting hole) had HUGE cracks in them, the crack in the locating hole allowed the distributor locating cover to be 2mm off of centerline.



The secondary boss (just the threaded boss) was cracked so badly that a piece of the boss came off in my hand when I touched it, I think the tension from the bolt was the only thing holding it on.......so looking at the exploded view on DCauto, I can only assume I get to redo the timing belt job I just paid $900 to do.....on top of getting to track down a new cover. I feel that the ticking from the distributor cap is probably the reason I heard the tech at the shop revving the engine to 5k+ immediately after it got off the lift....nothing smooths out that pesky interference like high speed revolutions! I guess my car also functions as a lathe!



Looking at the issue, it looks to me like this is a foundry/design issue, these bosses do not seem to have nearly enough flow to them during the casting process to ensure a strong, crack free casting. Ideally this section should have been cast with the two bosses as 1, and either left together, or split with a milling pass.....WTF Porsche!



Ugh!

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[tamathumper]

Someone was working on getting that casting redone, but I don't know what ever became of it. If I can get my hands on a good one (other than mine) I'll try to laser scan it for a 3D model.

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[flash]

as i heard it, they no longer work where they could have gotten it done

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[MB968]

[quote name='tamathumper' timestamp='1334794027' post='125573']

Someone was working on getting that casting redone, but I don't know what ever became of it. If I can get my hands on a good one (other than mine) I'll try to laser scan it for a 3D model.

[/quote]



Wish I had known, I could have sent you the one that I've had for the past couple of months. I will have the old one off, you'd just have to use CAD to correct the boss that is corroded away. Let me know if that would help. You can always use the mating part for the CAD info is missing.

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[shelby987]

Thinking about getting it scanned myself, I have a friend who owns a machine shop, so I might be able to get it made from the 3D data. There looks to be a lot of material conservation in this part for the sake of weight/cost reduction. The result seems to be an extremely light, fragile, and expensive part. I think this could be knocked out in a couple of hours at a machine shop, I am wondering if there is a market for this though? To make it look exactly like the original part will probably double the price....think the porsche community is more interested in an affordable, strong, reliable part or a factory appearance at twice the price?

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[MB968]

[quote name='shelby987' timestamp='1334793761' post='125569']

Well, I now know the source of the problem, when I got the two front covers off, it was painfully obvious! Both of the cast bosses (one being the locating hole, the other a mounting hole) had HUGE cracks in them, the crack in the locating hole allowed the distributor locating cover to be 2mm off of centerline.



. . .



Looking at the issue, it looks to me like this is a foundry/design issue, these bosses do not seem to have nearly enough flow to them during the casting process to ensure a strong, crack free casting. Ideally this section should have been cast with the two bosses as 1, and either left together, or split with a milling pass.....WTF Porsche!



Ugh!

[/quote]



Thats a bitch; was hoping that wasn't your problem. I know how bad I felt after finding the problem on my engine.



And, I wish it was as simple as a casting issue. The orig part was made from magnesium. The cracking is from what looks to me like galvanic corrosion resulting in the mushrooming of the boss as the corrosion spreads microscopically until failure.



The new part appears to be aluminum. The one I got from Sunset is a rev 08, even thought the latest rev # is an 09. I was told that the 08 and 09 could be identical but just sourced from different suppliers, but can't confirm.

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[shelby987]

[quote name='MB968' timestamp='1334796871' post='125577']

Wish I had known, I could have sent you the one that I've had for the past couple of months. I will have the old one off, you'd just have to use CAD to correct the boss that is corroded away. Let me know if that would help. You can always use the mating part for the CAD info is missing.

[/quote]



I had planned on using the front cover for the locating hole location, I might be interested in your mating part if you think it will be available shortly....otherwise I will have to use mine.

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[MB968]

[quote name='shelby987' timestamp='1334797122' post='125578']

Thinking about getting it scanned myself, I have a friend who owns a machine shop, so I might be able to get it made from the 3D data. There looks to be a lot of material conservation in this part for the sake of weight/cost reduction. The result seems to be an extremely light, fragile, and expensive part. I think this could be knocked out in a couple of hours at a machine shop, I am wondering if there is a market for this though? To make it look exactly like the original part will probably double the price....think the porsche community is more interested in an affordable, strong, reliable part or a factory appearance at twice the price?

[/quote]



If the part is machined from solid which is the most likely way to do it for a small batch, there would be no reason for it to be as thin walled as it is. Weight savings in aluminum would be minimal. It just needs to have all the proper clearances for the cam pulley/belts, and of course the cam position sensor.

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[WJH]

Mine's cracked too in the upper left hand corner where the bolt goes in. The <acronym title='previous owner'>PO</acronym> tried some type of JB Weld that all cracked out. I put a bolt with a nut on the back side to secure the two halves. What a crap design of a simple part. There is no way I'm paying $950 for a new one! They're smoking funny cigarettes at the Porsche parts house. There has got to be a better way.

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