Mystery Head Seals?

jstein · 03-24-2007, 06:13 PM

Hi Gang,

I'm in the midst of rebuilding a 3.0 SC motor with some local talent. In the catagory of "while you're in there" I scored a set of Mahle RSR P&Cs from fleabay which are replacing the CIS ones that came with the car (already have the Webers). We got the P&Cs on the block and assembled the heads, went to insert the head seals and

The ones that came with the top-end rebuild kit did not fit; not only were the seals a bit to wide to fit in the groove on the cylinders, but the diameter of that groove is larger than standard (as we measured).

Standard ID: 101.06mm
My ID : 102.8mm

We also tried a variety of seals sitting around the shop with no luck.

Any ideas?

MBruns · 03-25-2007, 11:06 AM

Sounds like the cyls. have been machined for the fire ring(935) style seals, you will have to have to have the heads machined and a custom fire ring machined to fit them.

Mike Bruns JBRacing.com

cstreit · cstreit's Garage

Mike,

Were the 935 rings 2mm smaller than the 3.0L CE/fire rings? ('cause the standard 95mm Mahle cylinders all had a fire ring groove)

These came off a hot street car, so there was a proper fire-ring in them before.

MBruns · 03-25-2007, 06:58 PM

If the SC seals wont fit and they are 95 mm bore they may be the 3.2 style or a mahle race set that never had a groove and had the 935 style added, most of which are custom and many different dimensions.

Mike Bruns

cstreit · cstreit's Garage

I see, thanks...

So where would would you go about finding a set of custom/935 CE rings?

Steve@Rennsport · 03-25-2007, 09:19 PM

Quote:

Originally posted by cstreit
I see, thanks...

So where would would you go about finding a set of custom/935 CE rings?

I would simply make them,....

Not cheap to do, but sometimes thats the only solution.

jstein · 03-25-2007, 10:24 PM

And I suppose it's a massively bad idea to leave these rings out.

Is this "simply" a matter of taking a cylinder to a machine shop and telling them to make a ring to fit the groove?

What material? What thickness (height)?

MBruns · 03-26-2007, 04:34 AM

If this is a street engine and the groove can be machined to accept the stock ce ring that would be the easiest fix, if not then the heads,cyls need to go to someone that can indicate the existing groove and properly put it in the head and then make a seal ring.

Mike Bruns JBRacing.com

jstein · 03-26-2007, 05:39 AM

Quote:

Originally posted by MBruns
If this is a street engine and the groove can be machined to accept the stock ce ring that would be the easiest fix, if not then the heads,cyls need to go to someone that can indicate the existing groove and properly put it in the head and then make a seal ring.

Mike Bruns JBRacing.com

Considering the existing groove is larger in diameter than the stock fire ring I don't think it would be that simple - unless some type of filler is used or welded in.

So I guess I have to find a machine shop that can handle this job - is this something a 'standard' auto machine place can handle, or is it more specialized?

What material is this made out of?

How thick should they be? Just the level of the cylinder head?

MBruns · 03-26-2007, 01:36 PM

I would send it to someone that has done them, as you only have one shot to get it right and the cost to experiment is usually time/materials, we get around 1000.00 to machine head and cyl. and make the fire rings (custom rings are around 100.00 ea.) we have done them in alum. and stainless the fit is critical to seal and not hold the head off from the cyl. If it goes wrong it will cost much more.

Mike Bruns

jstein · 03-26-2007, 03:50 PM

My "score" on eBay doesn't seem so awesome any longer.

What is the purpose of these rings?

Eagledriver · 03-26-2007, 05:28 PM

I think they are talking about something Bruce Anderson called "Ni-resist" rings. Maybe fire rings are a synonym. CE rings are what the stock engines used. The Ni-resist rings were a seal meant for high pressure turbo applications such as the 935. They sealed the seam at very high temps and pressures that would blow past a CE ring.

I'd be tempted to run with no seal and see if it leaked. I've heard that the CE rings don't do much anyway and the primary seal is the aluminum cylinder against the aluminum head. Later cars like the 3.2 and 3.6 had no CE ring. Of course they didn't have the groove either. If you are good at R and R ing the engine this might be an option. You could try "lapping" the barrels into the respective heads to improve your chances of success.

-Andy

len911 · 06:17 PM

Here are the Ni-Resist rings in my 3.2l engine. Bought engine in boxes and all machine work was already done. BTW, I think Ni-Resist is some kind of alloy chosen to work with the head's coefficient of expansion and be able to take the heat. Lou

cstreit · cstreit's Garage

$100 per seal?! Why?

You mentioned big issues, but 3.0L cars run with broken head studs and leaking heads for years without catastrophe, what am I missing?

The standard CE ring is a piece of aluminum with a spring inside it to help it flex. This is a 9.5:1 compression 3.0L engine not a 24psi turbo application, the CE ring doesn't do squat for these engines... The 3.2 didn't have them and there are no relevent mechanical design differences between the two heads. I'm sure Porsche decided that to.

My 3.0L bored out to 3.3L runs much higher compression and doesn't use or need them either. It has a flat surface like the 3.2

So why would you need $1600 worth of work on these particular heads??

If that's the cost from EBS (I'll post back, they do them a lot too apparently) I'm tempted to just use JayJ's solution of a graphite packing ring. It'll compress and withstand the temps. Either that or we'll have the local med place make 'em...

cstreit · cstreit's Garage

Len, I'm not familiar with that design. These cylinders have a groove, your's seem to have something else, please explain.

MBruns · 03-26-2007, 07:14 PM

The Ni-resist,fire ring etc.. are machined from tubular material,that has been machined inside and out parted off then ground flat to a certain thickness, it is just time consuming. As far as the stock CE rings they dont do much and they were designed to seal oil and combustion stains more than pressure. The 1000.00 includes the rings,machining the seal surfaces,cutting the groove in both the head and cyl. I agree it is not needed for a street engine but his question started out "what do I have here"

Mike Bruns

cstreit · cstreit's Garage

Mike,

Thanks for the clarification. The cost makes more sense! (and I certainly agree this isn;t something to experiment on.)

I did some research and apparently there were a number of variations in the size of the groove in these cylinders, especially since the 95mm were used in a number of different applications. He's already got the groove in the cylinders and in a perfect world we'd find the CE ring to fit it. Failing that we need to just machine the seals themselves or find an alternate material (such as the graphite).

In fact I'd love to try the graphite to see how it holds up in these engines, but I don't like to test on someone elses engine.

len911 · 03-27-2007, 04:11 AM

Chris, its pretty simple, perhaps pictures don't show it well, but both cylinder and head have a grove. Ring fits inside both locking them together. First pix shows groove in head, last two show ring in cyl ready to receive groove from head. Ring extends past the uppermost cyl surface. Its like tongue and groove furniture construction. I agree with Mike, the dimensions have to be pretty well controlled since you want good sealing. Lou

cstreit · cstreit's Garage

Len, I gotcha. I didn't know the ring was already in there...