One clearance that is often taken for granted in an engine building project is the deck clearance.
This is the distance between the crown of the piston and the deck surface of the block when the piston is at top dead centre.
This clearance affects the clearance between the piston and the cylinder head as well as the piston to valve clearance and the compression ratio.
While the deck clearance can be calculated from the specifications from the engine and parts manufacturers, it's easy for this to end up inaccurate if the deck of the block has been surfaced several times.
It's easy however to measure the deck clearance using a deck bridge as pictured. This tool is a fixture that holds a dial gauge which is zeroed on the block's deck surface. Once the dial gauge is zeroed, it can be moved over the piston crown and we can measure exactly where the piston crown sits in relation to the deck surface at TDC.
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