Usage of fire rings

[PeePee]

I know, that some engine builders have used fire rings on cylinders when building race engines. At the same time I also know, that some don't use them still being successful with the outcome.
Can someone say, whether there is some kind of boarderline when fire rings should be used, or what really is the philosophy?
Aren't they originally intended for preventing the head from forming oily carbon deposits?

[okayfine]

fire rings = o-ringing the block?

[bertvorgon]

If you are going to run insane boost, where cylinder pressures will be huge, then you might consider a fire ring set-up. The diesel guys use this a lot. Fire rings just kinda replace the sealing ring at the edge of the head gasket, where it is at the edge of the cylinder.

The classic "O' ring works very well for 99% of most engines needs.

I have never seen Specialty, in all his years of race engine building, ever resort to a fire ring, never a gasket problem.

I have 10:1 compression in my motor, then throw 16 PSI boost at it, never a problem, block is "O" ringed.

[Dave Patten]

The A15 engine in my Datsun 1200 racecar is around 15:1. I do not have an o-ringed block, but it needs to be.

Head gaskets are a maintenance item for that engine. They must be replaced after every other race weekend or you will have a guaranteed failure.

Conversely I've run 12.5:1 in an L20b race engine, no o-rings and never had a gasket failure.

[PeePee]

Dave, have you used a steel gasket in your A15 engine?

[McWicked]

Maybe I'm wrong... but aren't "fire rings" and "o-rings" two different (but functionally similar) animals?

-McWicked

[bertvorgon]

Yes.

[datzenmike]

I have a question, hope it's ok here.

I want to run a thin 0.020" copper head gasket which by itself should work fine but I want a bit more insurance just in case I change my mind on the compression later. I'm going for 8.9 . I should have had the block ringed while it was at the shop.

Would beading the copper edge around the cylinders improve the seal? Head and block have been fresh machined flat.

[Paul J]

We ran a copper o ring on our VG30 engine with over 13 to 1 and factory composite style gasket. We had some old L28 engines that ran a cooper ring (wills ring) style groove in the block with a special gasket, the groove in the block was similar to a Triumph TR6 or TR250. This style of gasket worked well but was costly. The copper or stainless rings are usually fine for most applications and the machining step is reasonable. I think the cost for the other gaskets and machining makes it cost prohibitive for most customers, but we really don't do any hp diesel work either. I'm not sure about the carbon deposits, but it sounds reasonable. I like the idea of the 'fuse' being the gasket vs the head getting torched as the flame tries to escape. The other consideration is the gasket, we usually do not o-ring when using a MLS gasket. Hope this helps.
Paul

[bertvorgon]

I dunno Mike, even though copper can deform quite nicely, could you really get the 'beading" to be really uniform? As you have nice fresh surfaces, and relatively low compression, why introduce the potential for an issue.

[datzenmike]

It's not high compression. I guess just flat copper should work then? Annealed? to soften it.

How far does an O ring sit above the block? About 20% of the head gasket thickness?

[Byron510]

It's not high compression. I guess just flat copper should work then? Annealed? to soften it.

How far does an O ring sit above the block? About 20% of the head gasket thickness?

It's not much Mike, maybe. 005-.010"

I'd be concerned about your copper head gasket idea. I see where you are coming from, but with the different expansion rates between the aluminum and the cast iron (which are extreme where metals are concerned), I would worry about sealing of both the oil and the water passages. Gaskets were designed of composites for a reason, and I feel this was the highest priority on the engineers lists. For a race application only acquiring a few hours of use before tear down - that's a different story. But a long term street engine, I don't think I like the idea.
It's just an opinion, from a machinists point of view. But if you do go ahead with this, I'd really like to following long term. Maybe I'm right out to lunch and wouldn't be afraid to admit it if you prove that this works for you. I'll certainly stay tuned.

But back to the "O" rings. The ones I've seen are simply stainless wire carefully pressed into a grove machined into the block deck, designed to place extra force on the fire crush rings built into the head gasket. That simple.

Byron

[bertvorgon]

Yah, anything I have seen at Andy's, including my own, is maybe in the .010-.020 proud. I could ask Andy if you like.

[McWicked]

I'd be concerned about your copper head gasket idea. I see where you are coming from, but with the different expansion rates between the aluminum and the cast iron (which are extreme where metals are concerned), I would worry about sealing of both the oil and the water passages.

Differential thermal expansion is often an exaggerated concern. Sure, most aluminum alloys have about twice the expansion rate of ductile gray iron, but as employed in an engine, this doesn't impose a significant hurdle.

Gaskets were designed of composites for a reason, and I feel this was the highest priority on the engineers lists.

The priorities would be cost and cost. Composites are cheaper to make and have lower failure rates during initial engine assembly in the factory.

-McWicked

[datzenmike]

Well straight copper is used on high compression engines that would fail with composites. I was thinking a little extra insurance. Block was decked 1mm and so was the head for super flat smooth surface. Need some copper-kote or equivalent dressing. Have to anneal the gasket and find some good head bolts. Z20 or Z22 may work.