Other Fucking Message Boards that Suck Major Ass!

[Cat_Whisperer]

@The Great Sun Jester

Lots of pressure between the bottom of the head and the top of the block. In fact, that seam is under THE highest pressure of all parts of the engine ever and it’s potentially the weakest link in the combustion chamber. It has to contain the fuel-air mix when it is compressed at the maximum point, and it has to contain the initial explosion that eventually pushes the piston back down. With that in mind:

When you get all the head bolts “started” there is still a good bit of room to wiggle the head around on top of gasket between it and the block. If you were to tighten the bolts down on one end and then the other, and then go after the ones in the middle, you can end up with uneven pressure at some parts of the gasket surface between the head and block. As a result you have introduced a weaker point in that seam. With the pressures we’re talking about such weak areas will fail far sooner than they would otherwise. By tightening from the center and working your way toward the outermost bolts, you’ve got a better shot of avoiding that problem. Think of it like smoothing a blanket on a bed, aiming to get rid of any wrinkles while making sure the blanket stays centered on the bed (because you’re just OCD that way). It’s sort of instinctive to put your hands on the middle of the blanket and move them toward opposite ends. Doing it multiple times, heading for higher torque each time, further ensures even pressure at all points of the mating surface.

@Amateur_Barbarian

Most mechanical assemblies have to be tightened together carefully to keep from misaligning or distorting components. Heads are the classic example - if you tighten the bolts in the wrong order, or tighten any one too much at one time, you will get warpage between the head and deck of of the block, and various kinds of leakage and premature failure.

It is one of the most critical steps in engine repair, especially with aluminum heads, to tighten the head bolts in exactly the right order, in two to four carefully calibrated stages, in order to get a precise, flat, warp- and leak-free seal that will last 100K miles or more. (It’s also important to have the bolt holes or stud threads clean and lightly lubricated, so that the torque readings in each stage are consistent and accurate.) You can get away with a little slop if you’re throwing together an iron Chevy motor for a driver; when it comes to higher and higher performance engines, the care you can use knows no bounds. When you get to 4,000HP drag engines, you’re exceeding the care used to assemble ICBM systems.

This is so typical of the Dope - start a flaming Pit thread, and next thing you know, actual information starts getting flung about.