05-11-2018, 08:50 PM
The coefficient of linear expansion of cast iron is about 10% lower than steel, so if we disregard temperature-related friction effects and the rather thin layer of copper in the gasket, the axial force in the studs will slightly reduce when the engine warms up. As the amount of this reduction is relatively small it's not a big deal whether the 'coup de grace' is applied hot or cold. The nuts will probably nudge up a fraction and when it cools down the clamping force will be slightly higher than it was cold. You could achieve the same effect by applying a marginally higher torque in cold condition. Where cold wins out is that it is a known and stable condition, whereas a hot engine is how hot? and gradually cooling as you work your way around the nuts, unless you tighten with the engine running. The main benefit of using a torque wrench is consistency but this is undermined somewhat if conditions are changing as you use it. Either way, for a cast iron head with decent studs you will get away with it. An alloy head is an entirely different kettle of fish as aluminium expands twice as much per degree of temperature rise as steel. This means not just that the effect is reversed but that the differential expansion is greatly increased. Torqueing up an alloy head while it is hot will lead to leaking gaskets and potentially a warped head.
I would not advocate skimming block faces unless you absolutely have to. There is a surprisingly small margin against the stroke of the piston, take too much off and you are forever after stuck with having to skim piston crowns or space under the block to keep the pistons from hitting the head.
I would not advocate skimming block faces unless you absolutely have to. There is a surprisingly small margin against the stroke of the piston, take too much off and you are forever after stuck with having to skim piston crowns or space under the block to keep the pistons from hitting the head.