Headgasketless Engines
Headgasketless Engines
(OP)
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...
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...





RE: Headgasketless Engines
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.
RE: Headgasketless Engines
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.
RE: Headgasketless Engines
There's nothing wrong with head gaskets. The problem lies with the lack of stiffness in the cylinder head/block design.
RE: Headgasketless Engines
RE: Headgasketless Engines
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Headgasketless Engines
RE: Headgasketless Engines
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 www.helicoflex.com. 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.
RE: Headgasketless Engines
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http://www.sealco.co.uk/metaloandc.htm
http://www.sae.org/technical/standards/MA2538
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RE: Headgasketless Engines
RE: Headgasketless Engines
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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RE: Headgasketless Engines
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
RE: Headgasketless Engines
RE: Headgasketless Engines
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?
RE: Headgasketless Engines
99 Dodge CTD dually.
RE: Headgasketless Engines
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- http://www.headgasket.com/index.html