Here, you can see the gasket...
Here, you can see the gasket before the head has been bolted down. The embossing on the two outside layers of steel is holding the head up. Once the head has been torqued down, the layers will compress but can spring back out if necessary to maintain gasket seal if the head moves.
"Another added benefit is the gaskets are a uniform thickness allowing for a better clamp load distribution from the head into the block which in turn reduces overall bore distortion and improves piston ring seal. Composite gaskets focus the majority of the clamping load to the cylinder bore because of the fire rings that are typically used are thicker than the overall gasket."
Another useful feature of the MLS design is that it's easy to use the gasket as a method for dialing in the exact compression ratio you need. By making the inner piece (or pieces) of stainless steel thicker or thinner, you can control the compressed thickness of the gasket without affecting the quality of the seal.
To achieve the proper bolt...
To achieve the proper bolt stretch the torque values need to be consistent. This means the bolt threads must be lubricated. Many engine builders use ARP’s Ultra-Torque lubricant and Dorton says it works well, but he says he’s used extreme pressure lube for years with no problems so he sticks with that. What you use as a lubricant isn’t as important as long as your bolt manufacturer provides a torque value to use with that specific lube. Because different lubricants have different lubricating properties, the torque value you use will be different depending on the lubricant. Don’t forget to lubricate both sides of the washer as well as the underside of the nut or bolt flange as well.
"Cometic offers gasket thicknesses from 0.027-inch up to 0.140," Kistner says. "We design our MLS gaskets in a way that allows all thickness to seal equally. (But) the engine builder does need to keep in mind that intake manifold fitment and pushrod length need to be checked if the thickness of the head gasket has been changed drastically."
Better Bolts
"Head gaskets in general are extremely dependent on the head fasteners, torque values, and procedures," Kistner adds. "In fact, this is one of the main causes that leads to premature gasket failure. Cometic's MLS head gaskets will seal with stock bolts and stock torque values, however, if the cylinder pressure of the engine is enough to overcome the tensile strength of those bolts then the heads could lift the block enough to compromise the gasket. This is why so many engine builders prefer the use of aftermarket head studs made from stronger materials that have a higher resistance to stretching."
The SB2 cylinder head definitely...
The SB2 cylinder head definitely adds a bit of complexity to installation. In addition to bolt holes that extend through the water jacket, others must be accessed through the intake ports. After they have been torqued properly, Dorton uses a machined threaded plug that seals off the intake port while maintaining the optimum port shape.
In other words, it doesn't matter if you're using premium gaskets in your engine build if the head bolts you've chosen aren't up to the job. Quality aftermarket fasteners are more expensive, but they will prove their worth, not only in improved sealing ability but also in the fact that they are reusable through multiple engine rebuilds while stock head bolts should be thrown out after every rebuild.
To give you a better idea of the best practices when it comes to installing a set of cylinder heads and getting optimum gasket seal, we visited the shops of Automotive Specialists where owner Keith Dorton was working on an ARCA SB2 race engine. We thought it would be interesting to show you an SB2 because, while you may never see these heads in Street Stock racing classes, it's becoming more accepted in other classes.
All the basic concepts are still the same no matter if you're working on the traditional Chevy small-block (the head bolt pattern is even the same) or a Ford Windsor. The complexity of the SB2 head just requires a few extra precautions. And a little extra time up front will result in better performance down the road.
Here’s another view of the...
Here’s another view of the access holes for the head studs. Once the port plugs are in place they will be covered by the rocker stands. This means if you need to pull a cylinder head, the valvetrain must be completely stripped first.
Properly torquing the bolts...
Properly torquing the bolts or studs used to connect the head to the block is critical in order to get optimum gasket seal. First, the fasteners must be tightened in a specific pattern. Begin with the centermost fastener and work your way outward in a spiral pattern. Whether you go clockwise or counterclockwise is up to you as long as you’re consistent. Also, you should also reach your final torque value in three steps. For example, if your goal is to torque the head studs to 60 ft-lb, begin by torquing all the bolts to 40 ft-lb first. Then go back a second time and increase the torque to 50 (you don’t need to loosen them first). Finally, on the third go-round, you can hit the 60 ft-lb mark for the completed process.
The nuts on the exhaust side...
The nuts on the exhaust side of the heads can’t be reached directly from above, so Dorton has to use this crowfoot-style extension. This changes the leverage the torque wrench has on the nut, so make sure to use the shortest extension you can get away with.