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Headgasketless Engines 1

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NakedTestMonkey

NakedTestMonkey

Chemical
Jun 17, 2005
20
I noticed the Subaru's in WRC are using a "headgasketless" (in the normal sense of a single MLS or graphite gasket) design in order to improve cylinder sealing under high boost situations. It involves using a compressible ring in order to provide chamber seal and the remaining seal is bare metal to metal contact (from what I can make out).

It has been suggested that this is a method to reduce shear stress as well as reducing necessary clamping loads via the head studs (reducing cylinder distortion).

My questions are.

1. What is the realism of using this on a street driven vehicle?

2. To what degree would you suggest polishing the surfaces. I know the MLS gaskets require more surface polishing in order to properly seal, but wouldn't the removal of the gasket create a greater need for super-fine polishing of the connected surfaces? Would a less than optimal surface introduce questionable amounts shear due to surface friction?

3. Since the Subaru is using a 2-cyl. per bank configuration would this technology be of lesser benefit in the reduction of head distortion (lift) in a similar large bore / short stroke inline 4-cyl motor due to the transfer of internal forces through-out the head?

4. Clamping loads are reduced because of the increase in surface uniformity? (reduction of riser points?)

My hobby is turning into another degree...
 
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O-rings are used instead of head gaskets on some high performance applications besides Subaru, I've heard of it being done on other engines. Whether it's possible or not depends on whether there is enough metal in the required areas to machine the groove for the O-ring. I've never done it myself, but one would think that there is an O-ring for each cylinder to contain the cylinder, an O-ring for each lubrication passage, and a big "O" ring all the way around to contain the coolant, unless they're relying on sealant for the coolant (which is possible). Shouldn't matter how many cylinders.

I don't think you can reduce the clamping loads, you need enough total clamping force to resist the combustion pressure. If the block-to-head joint separates even minutely, there is going to be trouble.
 
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The "right" way to do this was done in ancient (1950s) days with the Offenhauser racing engines. Integral cylinder head, cast with the cylinder block. Of course if you asked some foundry to do that today they would panic and tell you it's impossible. The corvair engine was originally designed to be made the same way, but that was declared daunting and changed to the design they sold which only leaked a couple of quarts overnight usually. At least Soobs are water-cooled and the engine does not go through such dramatic heat-cool cycles as the (air-cooled) corvair. The 04 Soob forester XT in my garage hasn't dripped oil yet.

The Chevy Vega engine became a paragon of reliability (not!) because of radial elasticity of the (aluminum) cylinders wearing the head gasket. Coolant and oil mixed which resulted in an effective nonlubricant and scored cylinders. When the Cosworth high-performance mods were incorporated, higher combustion pressures were expected so they used a metallic o-ring to key the cylinders to the head.

 
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Commercial diesel engines run at significantly higher peak cycle pressures, and for thousands of hours longer, than any turbocharged gasoline racing engine. And by the way, they utilize head gaskets.

There's nothing wrong with head gaskets. The problem lies with the lack of stiffness in the cylinder head/block design.
 
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Older Porsche aircooled flat fours had no head gaskets at all, which they proudly advertised as not necessary due to superior design and machining. My Briggs 5hp engines don't have them either, no problems with increased compression. Concerning the Corvair, the OEM Buna N pushrod tube o-rings couldn't handle the 350 degree F head temp for long, the Viton o-rings fix this. We used to lap the cylinder barrels to the heads on VW's and Corvair's years ago, worked like a top.
 
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One fix for aluminium engines in the sixties/seventies was either Mills or Dykes rings (can't remember) . A circular groove is milled into the head and the liner and a metal ring is dropped in to form the seal around the cylinder. Used on Top Fuel engines these days.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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Greg, that's exactly what I am referring to. Could you elaborate on it's benefits please?
 
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Yes, o-rings can be used to seal heads.

A rubber o-ring is used in several Mercury outboards as a cylinder block to head seal. However, 1) the two stroke cylinder pressures are generally lower than 4 strokes, 2) there is usually lots of room between the cylinders (to accomodate ports) - so there is room for the grooves and 3) outboard coolant temps are low, 120/130 F to keep deposits from building up in the engines - helpingthe rubber to live

The ultimate combustion seal might be the hollow metal o-rings that are pressurized inside. See for example I believe ther is an old book on diesels that discusses this point. (Anybody know the title/author?)

VW flat fours ran without head gaskets. The surface machining was not highly polished.

The clamp load should be three or more times the peak force from the gas load as a general rule.
 
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Oh yeah, and don't forget, you'll need some method of sealing the coolant and oil passages.
 
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One problem with gasketless head is to ensure a totally flat surface, no pitting or scratches. On the VW's and other application with free standing cylinders and a one piece head, ensuring a TOTALLY equal installed deck height was almost but not fully impossible, leading to tapered sealing surfaces.

Head gaskets have come a long way since the 60's and for all practical purposes, there is no reason for running a head gasketless engine (but other sealing surfaces work just fine with "form in place" gaskets.

Franz

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"Dry deck" and "wet deck" 'gasketless' cyl head to block applications is nothing new...it's been around for decades.
My first view of a dry deck was a Ford Trans-Am race car 302 Cleveland (as was my first view of a 'wet deck')back in the early 70's, but I have since read about the process being applied in several other race engines (IRL Chebbys, etc.)...not the least of which is my own little A series Mini engine. I don't see the big deal here.

Rod
 
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All the aircooled aircraft engines that I know of do not use a head gasket. The barrels (cylinders) are shrunk screwed into the aluminum heads. It is kinda funny when the performance industry thinks they have discoverd something new, and come to find out it was done half a century or more before. Such as turbocharging, NOS, billet crankchain parts etc. etc.
 
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Thanks for all the response.

The application is watercooled turbo inline engine with an open deck.

I suppose I could integrate the o-rings as the primary sealing of the cylinders and bore out a MLS headgasket to accomodate the rings and provide ample coolant / oil galley seal.

I'm going to address the open deck with a deck plate on stock iron sleeves to reduce the sleeve migration and reinforce the sleeve itself.

A primary concern I'm running into is head lift (pressurization of coolant system under combustion event). Are my planned alterations going in the right direction?
 
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The Ford Boss 429 used the oring seals. It was a real PIA to service one of these in a Mustang. It was really hard to get good seal to prevent oil leaks. The coolant wasn't a problem but getting all the metal to metal joins oil tight was. In the car it was tough just to get all the orings to stay in place while you set the heads on. Not to even discuss how tough it was to install the ...headers. There was no flatrate on these so what ever time and materials it took is what he customer paid. And it was never cheap. I hated the few of these that came in as getting paid hourly cost me dearly on the flatrate.

99 Dodge CTD dually.
 
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FWIW, a Dykes ring is a very thin and light weight "L" shaped top compression ring.

Also FWIW, Detroit Diesels use a crush ring for the liner to head seal, and rubber/silicone O-rings for everything else.

Lots of race engines at all levels use copper head gaskets. Try googling "copper head gaskets".
Some info here-
nwesm.jpg
 
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