Sealing the heads.

Instead of O rings in the head and reciever grooves in the block, has any one used the brass fire rings with the copper gasket there just to seal water or take up the gap if running dry? Sports compact stuff use them almost exclusive and making big boost numbers.

 

Not quite sure what you are asking here?............

 

If you are talking about the SCE gaskets, I ran those once on a hemi block that had a oring groove with wedge water heads. I didn't have a blower but they sealed well.

Dave

 

What is a "fire hoop"?

 

Stainless hoop in the heads??

 

Is the stainless ring in the block or heads?
What is the brand of head gasket that Will Hanna is talking about?

 

This is what I was talking about. Has anyone used this set up?

 

Was before my time, but I am told they used to do something similar in Top Fuel for a brief period. That idea was eventually abandoned in favour of what is now known as the "Fire Hoops" used by Top Fuel (and alcohol) teams.

They used to use a stainless stepped ring similar to the one shown above, with a surrounding aluminum or copper spacer gasket to simply act as a spacer and to seal off oil migration.

In a perfect world, if every bore hole was exactly equal in height to the neighboring ones beside or near it, then the system worked pretty good I am told. The problem became that not every bore hole was always in fact ever equal in height. You can picture what might happen in the "low" bore holes due to less or little clamp load. Now if the ring had been compressible, or crushable, then a different outcome might have resulted. Similar copper rings have some crushability, and then we will talk about gas filled rings below.

The fire hoop approach is pretty bullet proof and it is a bit more forgiving of machining tolerance variation given that the copper gasket offers a bit of compliance and squishability (is that a word?) at the time of assembly.

Think of a fire hoop as a solid, contiguous, stainless steel hoop or ring. If you were to cut the ring in cross-section you would note that one face is basically flat, while the opposite face is basically bull nosed.

The flat face seats into a cut groove in the cylinder head, and thereby does not significantly brinnel the head over time and use. The bull nosed face squeezes the copper gasket into a receiver groove cut into the top of the sleeve.

Each hoop basically tries to extrude and squish the copper gasket material as required, which in turn takes up slight variations from bore hole to bore hole while creating an optimal seal around each bore.

Upon tear down and reassembly, the copper gasket is in a sense the renewable sealing surface. If it looks okay, then maybe re-use it for a few more tries. If it looks suspect, then toss it. Low cost, easy to replace.

There is yet another way to seal the bore holes, which is a hybrid of the video ring first discussed above. I have many engines here which use this method, but as I tear them down I am intentionally trying to move them away from it since it is a too fussy and expensive method of sealing.

There are rings called Wills rings, or Cooper rings, or gas loaded metal sealing rings, which are essentially hollow, contiguous, stainless steel (or Inconnel) rings that are filled with an inert gas, and laser welded, and then dipped in silver or some other superficial metal coating. Think of these as big hollow gas filled rings that have some "squishability" (there's that word again) to them. They are commonly used in nuclear, aviation, and mission critical applications.

Again, a great solution in a super clean, super machined, world. However, they are prone to pressure spike failures during say the onset of knock or pre-ignition, and they cost on average $100 per bore hole, and they are one time use only.

Not nice knowing that if you pull the heads you've just spent about $800 to put it all back together. Best suited for engines that don't come apart often, and even better suited for engines with steel heads and blocks. These are used in endurance competition engines which go together carefully once, and then stay together for an extended period.

Hope this helps.

 

Should have added one more thought, but my timer has run out for editing. So here goes.........

A modern Top Fuel engine generates well over 13,000 psig of cylinder pressure when all is right with the world. Fire Hoops have proven to be able to harness these insane pressures. They have also been universally adopted by the fuel teams.

They are however a "Fuse" if something goes horribly wrong. They can and do let go at times, usually rendering the associated parts as salvageable as opposed to junk.

I tend to think that if there was a better way to seal, they'd have figured it out by now, but that does not appear to be the case.

Again, we are talking drag race engines only, often torn down, which undergo huge chamber pressures and short duration runs.

 

Thanks TOL. Reason for asking is I am building an endurance 520ci BBC engine for customer and we have been using O Ring in block with reciever grooves in head. { i know we will probably be better off with the O Ring in the head } After several instalations the reciever grooves start to loose the square shoulders which then starts showing signs of leak between the cylinders. When we do get any problems and head / block needs facing it tends to be a little bit of machining problems which we really try to avoid. Currently we run around 32 lbs and between 7800 - 8100 RPM in a circuit boat. We tend to step the boost up a bit more but am thinking of a better sealing method with less wear related issues. The video I shared with the fire rings is used a lot in sports compact big boost aplications. The copper gasket is only as a spacer and to seal water / oil only. Just undecided which way to go with the new engine.
I think with the BBC when we use O Rings / reciever grooves, there isn't much material left between the grooves for the gasket to bite into. This is mainly on the 4.500" and larger bores.
Do you have any pics on the fire hoops? Are they like a big version of the O ring? Does the head need machining to fit them as well as a reciever groove.
The fire rings have a groove only to locate them in the block and the top flat face seals directly on the head. The copper gasket is only a couple thou thinner so the rings are machined according to the gasket thickness you will be using.

 

Hi MKR-588.

I don't have the ability to post a photo on this forum, but if you send me your email I can shoot you some pics that way.

Your block and heads are iron/iron, or a mix of iron and aluminum? I am gathering from the sounds of what you have described that your heads are aluminum? If that is the case, and if the receiver grooves are in the heads, then yes you will see rounding of the head groove shoulders over time.

All of my stuff is big bore as well, ranging from 4.437 to 4.600, on 4.840 BBC bore centers. Most NA, but some blown alky or nitro.

You could use malleable copper alloy rings like you mention, but once crushed they have no spring-back or rebound apart from thermal growth. The same thing is true with the fire hoops to be honest, but again with them they don't "damage" the heads over time since the flat face fits into a flat cut groove in the head (think of the flat cut groove as a flat step register).

In either case you are always going to see a bit of leakage if used in an "endurance" application. The term endurance has many different meanings depending upon what one is doing.

The gas filled metal O-rings I mentioned are a good sealing "endurance" solution because they have inherent spring-back if installed correctly. They used to be produced under the name Garlock Helicoflex, but I believe there has been a merger(s) since and they are now available under the name Technetics. Here is a typical link https://technetics.com/products/sealing-solutions/metal-seals/o-flex/ . The ring options are endless, but their Tech department is very helpful.

Now in my case my blocks and heads are aluminum. A step notch gets cut into the top of the steel sleeve, which houses the metal O-ring. The O-ring protrudes past the top of the sleeve at rest, and is squished by the head deck. No spacer gasket. The ring squish is carefully adjusted so that the ring is squished by a fixed % of it's cross-sectional diameter, but not to the point where the O-ring is not able to spring-back. These provide excellent sealing once the engine is at operating temperature, but they do tend to leak a little when cold. The superficial metal ring coating plays a big role in this, as well as the machining roughness and the final machined squish target.

Apart from cost and machining, the only other downside to these hollow O-rings is that they tend to brinnel a groove into the aluminum heads over time in my case. How big a problem this is, is a function of clamp load, ring properties, machining tolerances, etc. Better if the heads and block are steel or iron (ie: diesel).

If pics or further thoughts might help, shoot me your email.

 

One more parting thought on these hollow metal O-Rings.........

Depending upon how exactly the O-ring groove is cut, and depending upon whether the O-ring body is directly in contact/communication with the combustion chamber pressures or not, there is the risk that the O-ring structure can be compromised by things such as pre-ignition, knock, detonation, etc.

Once compromised or failed, the O-ring will have ZERO cylinder sealing ability (this statement has to be qualified against the style of O-ring chosen initially), so that can be a problem too.

No free lunch, just a big menu board of options.