924Board.org

[MRElliott]

I’ve a question that I’m hoping someone “out there” can give me some guidance on. The question deals with replacing gaskets while installing a replacement turbocharger on a 1979 European spec 931 (VIN 9249400788).

I pulled the turbocharger and had it rebuilt, and when ordering new gaskets I noted that in the parts reference (PET parts CD) in addition to the hollow metal “O-rings”, there are flat gaskets as well. When I removed the turbo (a rebuilt unit itself, Porsche part # 931.123.002.FX, KKK part # 5326.970.7007) it only had the metal “O-rings” in these three places, no flat gaskets: exhaust manifold to turbo, exhaust manifold to “J” tube and turbo to exhaust pipe.

I went ahead and purchased the “O-rings” as well as all the flat gaskets, not knowing if when the unit I removed was installed it was done incorrectly or what. I plan on bolting things in place next weekend, and am hoping that someone can tell me which is correct: Just the “O-rings”, just the flats, or both. And, if both, on which side the O-rings should be placed.

I don’t have the part numbers with me right now, but can post them in a follow-up mail if that will help answer the question.

Thanks in advance,
Mark
Vicksburg, MS

[Smoothie]

It's been a while since I had my turbo out, but the parts list I have shows both sealing rings and flat gaskets on those 3 locations. Also, there's a "ring" 931.111.599.01 in addition to the "sealing ring" and "gasket" on the exhaust manifold to turbo connection. - Don't know if that normally needs replacement. From the manifold to the turbo, it shows: "ring", "sealing ring", "gasket". From the turbo to the exhaust pipe it shows: "gasket", then "sealing ring". From exhaust manifold to waste gate pipe it shows "gasket", then "sealing ring".

Never mind all this crap - better information below...

_________________
'82 931

[ This Message was edited by: smoothie on 2002-09-10 05:05 ]

[MRElliott]

I suppose part or most of my concern about this matter stems from the fact the car only had the rings installed when I took it apart - it seemed very odd to me. Plus, there are "notes" found on the PET parts CD which says something to the effect of use "this" gasket with "that" manifold, and "this" gasket with "that" turbo...

Also, there are notes at the following location in the "924 Garage" about the manifold, gaskets and turbocharger which also makes me wonder.
http://www.924.org/techsection/931_turbo.htm

Because it is an early Euro-spec model I've always been a bit hesitant to just bolt things together. I have the factory workshop manual, but it only covers US spec '80-'82 models, and I don't recall it saying anything at all about the gaskets other than to use new ones.

I appreciate everyone's input. I'm new to the Forum and find the entire 924.org site a very valuable resource.

Mark

[gohim]

When your car was built, it was made with flat gaskets. As time went on, Porsche switched to the crush rings that you have in your car. When the switch was made to rings, Porsche published Technical Bulletins (for mechanics with the paid subscription service) with photos, explaining which components were compatible in what combinations. The Technical Bulletins released by Porsche are reprinted into Books each year (which are available for sale), if you are not a member of the paid subscription service.

The crush rings require a groove to be cut in both of the mating surfaces. If the mating surfaces are flat, then you use the flat gasket. If the mating surfaces are grooved, then you use a ring. You use one or the other (flat or ring) at each mating connection, not both. The components with the flat surfaces have not been made for years, so if you have to replace an exhaust component or turbo, and the new component has a groove, then you also have to replace the mating component with one that has a ring groove.

Do not attempt to reuse any crush rings, as they are slightly crushed when the components are bolted together and torqued. The connection will leak if you do, and you will have to unbolt, and replace all the rings and gaskets again, as they are not reusable.

[ This Message was edited by: gohim on 2002-09-11 06:26 ]

[MRElliott]

WOW, what a wealth of institutional knowledge y'all have at hand!!

I'll have to scrutinize the flanges and see if the grooves are present, and I suspect they are. When I first pulled the unit, it was the first time I'd ever seen these crush rings used (military or civilian application). I looked at them closely to see how they work and saw that they were actually hollow.

They are slightly deformed (flattened), but not by much, so that sort of makes me think that there is a groove of some sort in the flanges. I'm guessing that without the groove the rings would REALLY be flattened out.

I'll do the part number search again and see if I can make positive sense out of the notes in the PET parts CD. Hopefully the exhaust manifold will have a number cast in it like the intake side does. But, I know that the turbocharger # noted is different than mine.

As a matter of curiosity, does anyone know the advantage in using them over a conventional gasket set up (other than the rings being 1/4 - or less - the price of the flat gaskets? Is this a Turbo thing, or does the normally aspirated 924 use them as well?

Thanks again y'all, I'll keep an eye on this Forum to see if others have $.02 to offer as well.

Mark

[Smoothie]

I'd say the rings provide a more reliable seal. I've seen those type of gaskets deteriorate - the type with asbestos or whatever sandwiched in between thin sheets of metal (aluminum?). The rings seem better suited to the high heat that those kinds of joints get.

[gohim]

You cannot go by the casting numbers on the parts on your car. They are not the part numbers used by Porsche. You need to look at the parts that you have to determine which connections are set up for crush rings, and which (if any) are set up for flat gaskets, then look at the parts books are order the appropriate crush ring or flat gasket that fits that particular location.

The crush rings create a more reliable, high temperature seal.

Unfortunately as you have already discovered, they are also many times more expensive than the earlier flat gaskets.

Crush rings are only used around the turbo plumbing on the 931.

1981 and later model 924s have larger diameter studs, and use crush rings on the exhaust manifold to collector connection. Earlier 924s use a flat gasket cost costs around $5, the later ones use (2) rings that cost over $20 each. Same problem with the larger nuts used on the later cars to connect the exhaust manifold to the collector. The smaller nuts are about $1.73 each, and the larger ones are over $12 each.

The flat gaskets and exhaust nuts used on the earlier 924s, and the early model 924 are 477 and 931 prefix numbers. The crush rings used on the later 924, and 931 models, and the larger exhaust nuts all have 930 prefix part numbers, so you know why the prices are jacked up.

[ This Message was edited by: gohim on 2002-09-10 08:38 ]

[Paul]

Well said Gohim!

The only thing I can add is, don't use both the flat gasket and the ring if you have grooved connections.

Don't ask me how I know.....

[ This Message was edited by: Paul on 2002-09-10 09:12 ]

[Lizard]

paul i like your sarcasm, there are other people who need to lighten up

[John H]

On the tuurbo to manifold connection if you are using teh sealing ring you shoudl also ensure that the manifold has a "fire ring" in the end of the manifold that sticks into the turbo. Also you should have these rings in each outlet of the cylinder head.

when the motor starts up the gaskets provide the initial seal and when the engine gets up to temperature the fire rings expand and provide a gas tight joint between the head and the manifold and between the manifold and the turbo.

If you dont have these you will find the flat gasket (if used) at the head will fail real quick

[MRElliott]

Hey everyone!

I'm sure glad I posted. I looked at things last night when I got home and what I found is that the turbo has a "recess" cut into the flanges on the turbine intake and exhaust ports. These recesses are the exact diameter as the crush rings' outer diameters, and about 3/4 of the ring's depth. So it would seem that using the rings is the correct way to assemble. The flange on the "J" bypass tube is flat, and I did not go into the garage and poke around at the exhaust manifold port. I suppose the right answer is as everyone is suggesting - if there is a groove (or recess) use the ring, if two flat mating surfaces, use the flat gasket.

John H, ... I didn't remove the manifold, so I don't know if the 'fire rings' you refer to (and I know what you are talking about) are present. And I can't recall what the manifold port --> turbine connection looks like. I pulled the turbo almost 11 years ago when it siezed up, and the car has sat idle, semi-assembled ever since. A long story, but I'm finally getting things back in order now that the car is almost a 'legal' antique.

I scrutinized the PET parts CD and found something interesting: It "notes" to use the crush rings with a turbo, part # such-and-such, and only with manifold part # this-and-that. But those part #'s aren't assigned to any year model. Go figure... <I understand the CD isn't the answer to all questions.>

As a side note on pricing: I didn't bring the invoice in to work with me this morning, but the flat gaskets were MUCH more expensive than the rings. If memory serves me right, they were like $28, $33 and $44, whereas the rings were in the $12-18 range. I suppose I just "threw away" about $100 in gaskets that won't be used... but better to have them and not need them, than need them and not have them, huh?

Mark