Surprise: Fire-rings in SC engine ?

[buster73]

Another surprise showed up while dismantling my new project engine (1980 Euro 930/09 188 hp bought used without any history). Already was pleased to find that the engine was converted to 9,8:1 compression pistons, together with all matching CIS components of a 930/10 204 hp engine earlier in its life. Now after taking a closer look at the cylinder heads (big port, 930.104.329.2R, casting K1926d), I was wondering why the CE-rings would not come out, only to realize, that heads were equipped with solid metal sealing rings. Looks somewhat like fire-rings or Ni-resist rings used in 935 and other exotic motors. After some massaging and a good dose of freezer spray I was able to get the rings out of the heads. They are non-magnetic but appear to be made from Aluminum rather than nickel alloy (too soft and flexible). The cross section is rectangular, 2 mm wide and 4.2 mm high. The corresponding groove in the head is 2 mm deep, leaving 2.2 mm of the ring protruding out of the head. Nice press fit between ring and groove in the head. The cylinders seems to be stock with a 3.0 mm wide and 2.2 mm deep groove which would normally hold the CE-rings.

Anyone aware if these rings were ever used in stock engines from the factory ?

If not, some previous owner must have done this modification, probably when converting the engine to high compression pistons. Still strange as I am not aware CE-rings can not cope with CR of 9,8:1 ?

Anyway regarding the rebuild I guess I can not go back to stock CE-rings because they will not seat properly with the groove in the head. I would just reuse the solid metal rings and expect they will seal properly once the heads are torqued down.

Any insight or advice appreciated !




Solid metal ring and standard CE-ring for comparison

[Mark Henry]

Spec it out and if it checks out reuse, only other alternative is new heads and P&C's.

[buster73]

Thanks, guess that`s what I will do. After doing some research on fire / flame/ Ni-resist rings my understanding is they do not really seal the combustion chamber, but are used to somewhat control head blow-by with high boost engines and keep everything aligned. The combustion chamber seal still is mainly down to the metal-to-metal sealing surface between cylinder head and cylinder. The fire rings are more a "second line of defense" if the head will lift of the cylinder (guess similar with CE-rings). Not planning to over-boost my SC, so whatever ring are in there should be fine. Anyway I have the bragging rights to run 935-Technology in my car .

[Neil Harvey]

This may be of interest. This is what we do to seal the 911 heads to their cylinders. One is the head gasket, which sets the crush on the sealing ring and stops the heads from banging on the cylinder tops. The other is the sealing ring.

We have all sizes or can make to suit the grooves in your heads/cylinders.

Neil

[buster73]

Thanks Neil,

amazing stuff. Are these copper alloy rings ?. Would be nice to have, but simply overkill for a normally aspirated SC engine with just around 200-220 hp. Engine will be just a spare engine built on a budget.

[Neil Harvey]

FYI,
We do this on all 911 engines Turbo or NA. They all leak between the heads and cylinders. Leakage lowers cylinder pressure and torque.

Look on any NA engine without sealing they will all show leakage.

Do they stop engines from running? No, but with the performance will be better as cylinder pressure is held in cylinder under compression.

[HaroldMHedge]

Neil,
For a Carrera 3.2L NA engine modified for 98mm cylinders (now 3.4L), is your head gasket a drop in or are head and/or cylinder modifications needed?

[Neil Harvey]

Originally Posted by HaroldMHedge

Neil,
For a Carrera 3.2L NA engine modified for 98mm cylinders (now 3.4L), is your head gasket a drop in or are head and/or cylinder modifications needed?

No. Both head and cylinder needs machining. The sealing rings fits into a groove in the head and cylinder under predetermined crush and the head gasket sits inside of this ring in its own groove machined into the head.

We have been doing this mod for years on all 911 MY's and a lot more recently on the later 964 and 993 engines.

Unfortunately, these air cooled engines suffer from leakage and the loss of compression just lowers the engines performance even in stock form.

[mikedsilva]

Originally Posted by Neil Harvey

No. Both head and cylinder needs machining. The sealing rings fits into a groove in the head and cylinder under predetermined crush and the head gasket sits inside of this ring in its own groove machined into the head.

We have been doing this mod for years on all 911 MY's and a lot more recently on the later 964 and 993 engines.

Unfortunately, these air cooled engines suffer from leakage and the loss of compression just lowers the engines performance even in stock form.

Amazing work as always.

[buster73]

Originally Posted by Neil Harvey

FYI,
We do this on all 911 engines Turbo or NA. ....

Thanks Neil,

interesting you see leakage being an issue even for NA cars. Will take this into consideration for my future projects.

[HaroldMHedge]

Thanks Neil for the clarification.